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  • 1. Arapan, S. C.
    et al.
    Korepov, S. V.
    Liberman, M. A.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Effect of the boundary roughness on the conductance of double quantum wire in a magnetic field2003In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 64, no 2, p. 239-245Article in journal (Refereed)
  • 2.
    Aurell, Erik
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Bo, Stefano
    Dias, Marcelo
    Eichhorn, Ralf
    Marino, Raffaele
    Diffusion of a Brownian ellipsoid in a force field2016In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 114, no 3, article id 30005Article in journal (Refereed)
    Abstract [en]

    We calculate the effective long-term convective velocity and dispersive motion of an ellipsoidal Brownian particle in three dimensions when it is subjected to a constant external force. This long-term motion results as a "net" average behavior from the particle rotation and translation on short time scales. Accordingly, we apply a systematic multi-scale technique to derive the effective equations of motion valid on long times. We verify our theoretical results by comparing them to numerical simulations.

  • 3.
    Aurell, Erik
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Pfitzner, Rene
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Gaussian belief with dynamic data and in dynamic network2009In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 87, no 6Article in journal (Refereed)
    Abstract [en]

    In this paper we analyze Belief Propagation over a Gaussian model in a dynamic environment. Recently, this has been proposed as a method to average local measurement values by a distributed protocol (Consensus Propagation, Moallemi C. C. and Van Roy B., IEEE Trans. Inf. Theory, 52 (2006) 4753) where the average is available for read-out at every single node. In the case that the underlying network is constant but the values to be averaged fluctuate ("dynamic data"), convergence and accuracy are determined by the spectral properties of an associated Ruelle-Perron-Frobenius operator. For Gaussian models on Erdos-Renyi graphs, numerical computation points to a spectral gap remaining in the large- size limit, implying exceptionally good scalability. In a model where the underlying network also fluctuates ("dynamic network"), averaging is more effective than in the dynamic data case. Altogether, this implies very good performance of these methods in very large systems, and opens a new field of statistical physics of large (and dynamic) information systems.

  • 4.
    Biltmo, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Henelius, Patrik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    The ferromagnetic transition and domain structure in LiHoF42009In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 87, no 2Article in journal (Refereed)
    Abstract [en]

    Using Monte Carlo simulations we verify that the rare-earth compound LiHoF4 is a very good realization of a dipolar Ising model. With only one free parameter our calculations for the magnetization, specific heat and inverse susceptibility match experimental data at a quantitative level in the 0.5-3 kelvin range, including the ferromagnetic transition at 1.53 K. Using parallel tempering methods and reaching system sizes up to 32000 dipoles with periodic boundary conditions, we are able to give evidence of the logarithmic corrections predicted in renormalization group theory. Due to the long range and angular dependence of the dipolar model, sample shape and domains play a crucial role in the ordered state. We consider surface corrections to Griffiths's theorem, which arise infinite macroscopic samples and lead to a theory of magnetic domains. We find a domain wall energy of 0.059 erg/cm(2) and predict that the ground-state domain structure for cylinders with a demagnetization factor N > 0 consists of thin parallel sheets of opposite magnetization, with a width depending on the demagnetization factor.

  • 5.
    Bishop, Adrian
    et al.
    Australian National University.
    Shames, Iman
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Link Operations for Slowing the Spread of Disease in Complex Networks2011In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 95, no 1, p. 18005-Article in journal (Refereed)
    Abstract [en]

    A variety of social, biological and communication networks can be modelled using graph theoretical tools. Similar graphical tools can be used to model the topology by which disease, errors, and/or other undesired phenomenon etc. is spread and propagated through such networks. Certain network operations are proposed in this work that can be used to slow the spread of diseases in complex network topologies. The approach considered in this work differs from existing techniques in that it is based on optimally removing (or immunizing) individual links in the network as opposed to individual nodes. A systematic algorithm is outlined to achieve this edgewise immunization via a relaxed convex optimization protocol.

  • 6.
    Bo, Stefano
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB. KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Aurell, Erik
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Eichhorn, Ralf
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Celani, Antonio
    Optimal stochastic transport in inhomogeneous thermal environments2013In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 103, no 1, p. 10010-Article in journal (Refereed)
    Abstract [en]

    We consider the optimization of the average entropy production in inhomogeneous temperature environments within the framework of stochastic thermodynamics. For systems modeled by Langevin equations (e.g. a colloidal particle in a heat bath) it has been recently shown that a space-dependent temperature breaks the time reversal symmetry of the fast velocity degrees of freedom resulting in an anomalous contribution to the entropy production of the overdamped dynamics. We show that optimization of entropy production is determined by an auxiliary deterministic problem formally analogous to motion on a curved manifold in a potential. The "anomalous contribution" to entropy plays the role of the potential and the inverse of the diffusion tensor is the metric. We also find that entropy production is not minimized by adiabatically slow, quasi-static protocols but there is a finite optimal duration for the transport process. As an example we discuss the case of a linearly space-dependent diffusion coefficient.

  • 7. Bochkarev, A. S.
    et al.
    Zamulko, S. O.
    Gorbatov, O. I.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Sidorenko, S. I.
    Puschnig, P.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    A single-volume approach for vacancy formation thermodynamics calculations2016In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 116, no 1, article id 16001Article in journal (Refereed)
    Abstract [en]

    The vacancy formation Gibbs free energy, enthalpy and entropy in fcc Al, Ag, Pd, Cu, and bcc Mo are determined by first-principles calculations using the quasi-harmonic approximation to account for vibrational contributions. We show that the Gibbs free energy can be determined with sufficient accuracy in a single-volume approach using the fixed equilibrium volume of the defect-free supercell. Although the partial contributions to the Gibbs free energy, namely, the formation enthalpy and entropy exhibit substantial errors when obtained directly in this approach, they can be computed from the Gibbs free energy using the proper thermodynamic relations. Compared to experimental data, the temperature dependence of the vacancy formation Gibbs free energy is accounted for at low temperatures, while it overestimates the measurements at high temperature, which is attributed to the neglect of anharmonic effects.

  • 8. Bostrom, M.
    et al.
    Malyi, O. I.
    Thiyam, Priyadarshini
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Berland, K.
    Brevik, I.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. University of Oslo, Norway.
    Parsons, D. F.
    The influence of Lifshitz forces and gas on premelting of ice within porous materials2016In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 115, no 1, article id 13001Article in journal (Refereed)
    Abstract [en]

    Premelting of ice within pores in earth materials is shown to depend on the presence of vapor layers. For thick vapor layers between ice and pore surfaces, a nanosized water sheet can be formed due to repulsive Lifshitz forces. In the absence of vapor layers, ice is inhibited from melting near pore surfaces. In between these limits, we find an enhancement of the water film thickness in silica and alumina pores. In the presence of metallic surface patches in the pore, the Lifshitz forces can dramatically widen the water film thickness, with potential complete melting of the ice surface.

  • 9.
    Boström, Mathias
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Huang, Dan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Yang, Weihong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Sernelius, Bo E.
    Lithium atom storage in nanoporous cellulose via surface-induced Li-2 breakage2013In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 104, no 6, p. 63003-Article in journal (Refereed)
    Abstract [en]

    We demonstrate a physical mechanism that enhances a splitting of diatomic Li-2 at cellulose surfaces. The origin of this splitting is a possible surface-induced diatomic-excited-state resonance repulsion. The atomic Li is then free to form either physical or chemical bonds with the cellulose surface and even diffuse into the cellulose layer structure. This allows for an enhanced storage capacity of atomic Li in nanoporous cellulose.

  • 10.
    Boström, Mathias
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Flerskalig materialmodellering.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Flerskalig materialmodellering.
    Parsons, Drew F.
    Ellingsen, Simen Å.
    Sernelius, Bo E.
    Atmospheric water droplets can catalyse atom pair break-up via surface-induced resonance repulsion2013In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 101, no 4, p. 43002-Article in journal (Refereed)
    Abstract [en]

    We present the theory for a retarded resonance interaction between two identical atoms near a dielectric surface. In free space the resonance interaction between isotropically excited atom pairs is attractive at all atom-atom separations. We illustrate numerically how this interaction between oxygen, sulphur, hydrogen, or nitrogen atom pairs may turn repulsive near water droplets. The results provide evidence of a mechanism causing excited state atom pair breakage to occur in the atmosphere near water droplets.

  • 11.
    Bouya, Ismaël
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. Université Paris Diderot, France.
    Dormy, E.
    Toward an asymptotic behaviour of the ABC dynamo2015In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 110, no 1, article id 14003Article in journal (Refereed)
    Abstract [en]

    The ABC flow was originally introduced by Arnol'd to investigate Lagrangian chaos. It soon became the prototype example to illustrate magnetic-field amplification via fast dynamo action, i.e. dynamo action exhibiting magnetic-field amplification on a typical timescale independent of the electrical resistivity of the medium. Even though this flow is the most classical example for this important class of dynamos (with application to large-scale astrophysical objects), it was recently pointed out (Bouya Ismaël and Dormy Emmanuel, Phys. Fluids, 25 (2013) 037103) that the fast dynamo nature of this flow was unclear, as the growth rate still depended on the magnetic Reynolds number at the largest values available so far . Using state-of-the-art high-performance computing, we present high-resolution simulations (up to 40963) and extend the value of Rm up to 5·105. Interestingly, even at these huge values, the growth rate of the leading eigenmode still depends on the controlling parameter and an asymptotic regime is not reached yet. We show that the maximum growth rate is a decreasing function of for the largest values of we could achieve (as anticipated in the above-mentioned paper). Slowly damped oscillations might indicate either a new mode crossing or that the system is approaching the limit of an essential spectrum.

  • 12.
    Carlson, Andreas
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Bellani, Gabriele
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Amberg, Gustav
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Contact line dissipation in short-time dynamic wetting2012In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 97, no 4Article in journal (Refereed)
    Abstract [en]

    Dynamic wetting of a solid surface is a process that is ubiquitous in Nature, and also of increasing technological importance. The underlying dissipative mechanisms are, however, still unclear. We present here short-time dynamic wetting experiments and numerical simulations, based on a phase field approach, of a droplet on a dry solid surface, where direct comparison of the two allows us to evaluate the different contributions from the numerics. We find that an important part of the dissipation may arise from a friction related to the motion of the contact line itself, and that this may be dominating both inertia and viscous friction in the flow adjacent to the contact line. A contact line friction factor appears in the theoretical formulation that can be distinguished and quantified, also in room temperature where other sources of dissipation are present. Water and glycerin-water mixtures on various surfaces have been investigated where we show the dependency of the friction factor on the nature of the surface, and the viscosity of the liquid.

  • 13.
    Carlson, Andreas
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Kim, P.
    Amberg, Gustav
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Stone, H. A.
    Short and long time drop dynamics on lubricated substrates2013In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 104, no 3, p. 34008-Article in journal (Refereed)
    Abstract [en]

    Liquid infiltrated solids have been proposed as functional solvent-phobic surfaces for handling single and multiphase flows. Implementation of such surfaces alters the interfacial transport phenomenon as compared to a dry substrate. To better understand the interface characteristics in such systems we study experimentally the dynamics of a pendant water drop in air that contacts a substrate coated by thin oil films. At short times the water drop is deformed by the oil that spreads onto the water-air interface, and the dynamics are characterized by inertial and viscous regimes. At late times, the the oil film under the drop relaxes either to a stable thin film or ruptures. In the thin film rupture regime, we measure the waiting time for the rupture as a function of the drop equilibrium contact angle on a dry substrate and the initial film height. The waiting time is rationalized by lubrication theory, which indicates that long-range intermolecular forces destabilize the oil-water interface and is the primary mechanism for the film drainage.

  • 14. Do-Quang, Minh
    et al.
    Shiomi, Junichiro
    Amberg, Gustav
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    When and how surface structure determines the dynamics of partial wetting2015In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 110, no 4, article id 46002Article in journal (Refereed)
    Abstract [en]

    The motion of a three phase contact line, as in a droplet spreading over a dry surface, is ubiquitous in nature and common in technology, but is still not well understood. As has been recently shown, line friction may play an important role in rapid dynamic wetting. Recognizing this as a sometimes dominating factor, we identify the possible scenarios for dynamic wetting of a partially wetting fluid, given the fluid and substrate properties. In doing so, we also reconcile the seemingly different interpretations of dynamic wetting that have been put forward in the recent literature. Copyright (C) EPLA, 2015

  • 15.
    Essen, Hanno
    KTH, School of Engineering Sciences (SCI), Mechanics, Theoretical and Applied Mechanics.
    Classical diamagnetism, magnetic interaction energies, and repulsive forces in magnetized plasmas2011In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 94, no 4, p. 47003-Article in journal (Refereed)
    Abstract [en]

    The Bohr-van Leeuwen theorem is often summarized as saying that there is no classical magnetic susceptibility, in particular no diamagnetism. This is seriously misleading. The theorem assumes position-dependent interactions but this is not required by classical physics. Since the work of Darwin in 1920 it has been known that the magnetism due to classical charged point particles can only be described by allowing velocity-dependent interactions in the Lagrangian. Legendre transformation to an approximate Hamiltonian can give an estimate of the Darwin diamagnetism for a system of charged point particles. Comparison with experiment, however, requires knowledge of the number of classically behaving electrons in the sample. A new repulsive effective many-body force, which should be relevant in plasmas, is predicted by the Hamiltonian.

  • 16.
    Essén, Hanno
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Magnetic energy per particle in constant current density2008In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 84, no 2Article in journal (Refereed)
    Abstract [en]

    We assume a constant current density in a homogeneous one-component plasma of infinite extent and calculate the resulting magnetic energy per particle. Our starting point is the conserved approximately relativistic (Darwin) energy for a system of electromagnetically interacting particles that arises from the neglect of radiation. For the idealized model of a homogeneous one-component plasma the energy only depends on the particle canonical momenta and the vector potential. The vector potential is then calculated in terms of the canonical momenta using recent theoretical advances and the plasma Hamiltonian is obtained. The result can be understood either as due to the energy lowering caused by the attraction of parallel currents or, alternatively, as due to the inductive inertia associated with the flow of net current.

  • 17.
    Essén, Hanno
    KTH, School of Engineering Sciences (SCI), Mechanics.
    The exact Darwin lagrangian2007In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 79, no 6Article in journal (Refereed)
    Abstract [en]

    Darwin (1920) noted that when radiation can be neglected it should be possible to eliminate the radiation degrees of freedom from the action of classical electrodynamics and keep the discrete particle degrees of freedom only. Darwin derived his well-known Lagrangian by series expansion in v/c keeping terms up to order (v/c)(2). Since radiation is due to acceleration the assumption of low speed should not be necessary. A Lagrangian is suggested that neglects radiation without assuming low speed. It cures deficiencies of the Darwin Lagrangian in the ultra-relativistic regime.

  • 18. Fiolhais, M. C. N.
    et al.
    Essen, Hanno
    KTH, School of Engineering Sciences (SCI), Mechanics, Theoretical and Applied Mechanics.
    Electromagnetic wave scattering by a superconductor2012In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 97, no 4, p. 44006-Article in journal (Refereed)
    Abstract [en]

    The interaction between radiation and superconductors is explored in this paper. In particular, the calculation of a plane standing wave scattered by an infinite cylindrical superconductor is performed by solving the Helmholtz equation in cylindrical coordinates. Numerical results computed up to O(77) of Bessel functions are presented for different wavelengths showing the appearance of a diffraction pattern.

  • 19.
    Fransson, Jonas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Angular conductance resonances of quantum dots non-collinearly coupled to ferromagnetic leads2005In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 70, no 6, p. 796-802Article in journal (Refereed)
    Abstract [en]

    The zero-bias conductance of quantum dots coupled to ferromagnetic leads is investigated. In the strong-coupling regime, it is found that the conductance is a non-monotonic function of the angle between the magnetisation directions in the two contacts. This behaviour is an effect of the presence of the leads which induces an angle-dependent spin-split of the quantum dot states, and spin-flip transitions between the quantum dot states whenever the magnetisation directions of the leads are non-collinear, which enhances the current density at the chemical potential. In the weak-coupling regime, the system reverts to normal spin valve character.

  • 20.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Kowalewski, Jacob
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Wu, J.
    Yue, Y.
    Dai, N.
    Thylén, Lars
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics. KTH, School of Information and Communication Technology (ICT), Centres, Kista Photonics Research Center, KPRC.
    Radiative and nonradiative recombination of photoexcited excitons in multi-shell-coated CdSe/CdS/ZnS quantum dots2009In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 86, no 3, p. 37003-Article in journal (Refereed)
    Abstract [en]

    Colloidal quantum dots (QDs) have been widely studied for nanophotonics and bioimaging applications for which the lifetime of their fluorescence is of critical importance. We report experimental and theoretical characterizations of dynamic optical properties of multi-shell-coated CdSe/CdS/ZnS QDs. Quantum-mechanical studies of fundamental optical excitations and Monte Carlo simulations of energy relaxation mechanisms indicate that the excitonic states are densely compacted in the QDs and are easily photoexcited by the laser pulse in the presence of nonradiative electron-phonon interactions. For spherical QDs, the decay time of spontaneous radiative emission of individual photoexcited excitonic states with zero angular momenta is found to be only tens of picoseconds. In our multi-shell QDs, high-energy excitonic states of nonzero angular momenta have to go through a number of nonradiative electron-phonon interaction steps in order to relax to zero-angular-momentum excitonic states for radiative emission, resulting in an effective fluorescence peak at about 2 ns in the photoncount-time relationship. This explains the measured long average fluorescence lifetime of 3.6 ns. Such a long lifetime facilitates the applications of colloidal QDs in areas such as QD-based solar cells, bioimaging and metamaterials.

  • 21. Grönlund, Andreas
    et al.
    Holme, Petter
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Minnhagen, Petter
    Dynamic scaling regimes of collective decision making2008In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 81, no 2, p. 28003-Article in journal (Refereed)
    Abstract [en]

    We investigate a social system of agents faced with a binary choice. We assume there is a correct, or beneficial, outcome of this choice. Furthermore, we assume agents are influenced by others in making their decision, and that the agents can obtain information that may guide them towards making a correct decision. The dynamic model we propose is of nonequilibrium type, converging to a final decision. We run it on random graphs and scale-free networks. On random graphs, we find two distinct regions in terms of the finalizing time-the time until all agents have finalized their decisions. On scale-free networks, on the other hand, there do not seem to be such distinct scaling regions.

  • 22. Gvozdic, D. M.
    et al.
    Ekenberg, Ulf
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Superefficient electric-field-induced spin-orbit splitting in strained p-type quantum wells2006In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 73, no 6, p. 927-933Article in journal (Refereed)
    Abstract [en]

    We investigate theoretically the efficiency of the Rashba effect, i.e. the spin-orbit splitting resulting from an electric field. In contrast to previous studies, where the carriers have usually been taken to be electrons, we focus on holes and are able to demonstrate remarkable improvements of the effect by several orders of magnitude. We also show that the frequently-neglected lattice-mismatch between GaAs and AlGaAs can be used to further enhance the efficiency of the wave vector splitting mechanism. The Rashba effect is the fundamental mechanism behind the Datta-Das spin transistor and we find that for a small electric field of 2 kV/cm the spin precession length becomes only 36nm.

  • 23. Holme, Petter
    Efficient local strategies for vaccination and network attack2004In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 68, no 6, p. 908-914Article in journal (Refereed)
    Abstract [en]

    We study how a fraction of a population should be vaccinated to most efficiently stop epidemics. Our starting point is that only local information-about the neighborhood of specific vertices-is usable in practice. For this reason we consider only local vaccination strategies. The efficiency of the vaccination strategies is investigated with both static and dynamic measures. We test the strategies on real-world networks and model networks with real-world characteristics. Among other things, we find that the most efficient strategy for many real-world situations is to iteratively vaccinate the neighbor of the previous vaccinee that has the most links out of the neighborhood.

  • 24. Holme, Petter
    Network dynamics of ongoing social relationships2003In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 64, no 3, p. 427-433Article in journal (Refereed)
    Abstract [en]

    Many recent large-scale studies of interaction networks have focused on networks of accumulated contacts. In this letter we explore social networks of ongoing relationships with an emphasis on dynamical aspects. We find a distribution of response times (times between consecutive contacts of different direction between two actors) that has a power law shape over a large range. We also argue that the distribution of relationship duration (the time between the first and last contacts between actors) is exponentially decaying. Methods to reanalyze the data to compensate for the finite sampling time are proposed. We find that the degree distribution for networks of ongoing contacts fits better to a power law than the degree distribution of the network of accumulated contacts do. We see that the clustering and assortative mixing coefficients are of the same order for networks of ongoing and accumulated contacts, and that the structural fluctuations of the former are rather large.

  • 25. Holme, Petter
    et al.
    Olsson, P.
    A zero-temperature study of vortex mobility in two-dimensional vortex glass models2002In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 60, no 3, p. 439-445Article in journal (Refereed)
    Abstract [en]

    Three different vortex glass models are studied by examining the energy barrier against vortex motion cross the system. In the two-dimensional gauge glass this energy barrier is found to increase logarithmically with system size which opens up for the existence of low-temperature phase with zero resistivity. Associated with the large-energy barriers is breaking of ergodicity which explains why the well-established results from equilibrium studies could fail. The behavior of the more realistic random pinning model is however different with decreasing energy barriers and no finite critical temperature.

  • 26.
    Huang, Dan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Ju, Zhiping
    Dou, Maofeng
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Yao, Chunmei
    Guo, Jin
    Investigation on AgGaSe2 for water splitting from first-principles calculations2014In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 105, no 3, p. 37007-Article in journal (Refereed)
    Abstract [en]

    The electronic structure of AgGaSe2 has been investigated as a photocatalyst candidate by first-principles calculation. Our results demonstrate that the band edge positions of bulk AgGaSe2 straddle the water redox potentials. From the band offset calculation, we find that Al-doping of AgGaSe2 shifts the conduction band minimum upwards, whereas Cu-doping of AgGaSe2 shifts the valence band maximum upwards. By (Ag, Cu)(Ga, Al)Se-2 alloying one can thereby tailor both the band edge positions and the band gap energy, and this effect provides an approach to optimize the band properties for overall water splitting. Moreover, AgGaSe2 forms a suitable junction with CuGaSe2 with a type-II band offset, which facilitates electron-hole separation. The AgGaSe2 and CuGaSe2 junction can be designed as a tandem photoelectrochemical device to improve the photocatalytic properties of the system.

  • 27. Huang, L. M.
    et al.
    Araujo, Carlos Moyses
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Magnetic and electronic properties of 3d transition-metal-doped In2O3: An ab initio study2009In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 87, no 2Article in journal (Refereed)
    Abstract [en]

    The magnetic and electronic properties of the transition metal (TM) (V, Cr, Mn, Fe, Co, Ni, Cu) doped In2O3 have been theoretically studied by using the density functional theory. When two TM ions are placed close to each other (TM-TM distance of about 3.4 angstrom), the ferromagnetic ordering is found to be the lowest-energy configuration. The only exception is Fe, which possesses a half-filled 3d band. However, for further separation distance of about 7.2 angstrom, only Co, Ni and Cu ions (having more than half-filled 3d band) still prefer the ferromagnetic orientation, while V, Cr, or Mn ions (having less than half-filled 3d band) prefer antiferromagnetic ordering. The energies of the 3d band for TM ions show a decrease with increasing TM atomic number. For V, Cr and Mn, the 3d bands are merged with the conduction band, and show less hybridization with the host valence band; while for Co, Ni and Cu, the 3d bands show strong hybridization with the host valence band mainly formed by the oxygen 2p state. In this situation, polarized holes are formed on the oxygen sites close to the TM ions. Moreover, V-doped In2O3 is found to meet the requirements for a strong donor-mediated ferromagnetism.

  • 28. Huang, L. M.
    et al.
    Århammar, Cecilia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Araujo, José
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Silvearv, F.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Tuning magnetic properties of In2O3 by control of intrinsic defects2010In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 89, no 4Article in journal (Refereed)
    Abstract [en]

    The electronic structure and magnetic properties of In2O3 with four kinds of intrinsic point defects (O vacancy, In interstitial, O interstitial, and In vacancy) have been theoretically studied using the density functional theory. The defect energy states of the O vacancy and In interstitial are close to the bottom of conduction band and act as shallow donors, while the defect energy states of the In vacancy and O interstitial are just above the top of the valence band and act as shallow acceptors. Without addition of any magnetic ions, all the hole states are completely spin polarized, while the electron states display no spin polarization. This implies that semiconducting In2O3 can display magnetic ordering, purely due to the intrinsic defects. However, the formation energies for neutral p-type defects are too high to be thermodynamically stable at reasonable temperatures. Nevertheless, it is shown that negative charging can greatly decrease the formation energies of p-type defects, simultaneously removing the local magnetic moments. We conlcude that V-In''' and O-I '' will be the dominant compensating defects as In2O3 is doped with TM ions, such as Sn, Mo, V and Cr. This result is consistent with the general view that the p-type defect is a key feature to mediate ferromagnetic coupling between transition metal ions of dilute concentration in metal oxides.

  • 29. Hussain, T.
    et al.
    De Sarkar, Abir
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Maark, T. A.
    Sun, Weiwei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Strain and doping effects on the energetics of hydrogen desorption from the MgH2 (001) surface2013In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 101, no 2, p. 27006-Article in journal (Refereed)
    Abstract [en]

    On the basis of first-principles calculations we have systematically investigated the energetics of hydrogen desorption from the MgH2 (001) surface. Based on total energy and electronic structure calculations, two modes namely strain and doping of selected dopants (Al, Si, Ti) and the combined effect of both on the dehydrogenation energies (ΔH) of MgH2 (001) systems have been analyzed. The maximum improvement in ΔH has been obtained with the combined effect of doping and strain. Among all the dopants, Al gives the lowest value of ΔH when the system Al-MgH2 is subjected to a 7.5% biaxial symmetric strain whereas the Si-MgH2 systems show the least improvement in ΔH. The doping of Ti on MgH 2 (001) is also very beneficial even without strain. The reduction in ΔH is caused by the charge localization on the metal atoms, destabilization and the weakening of metal-hydrogen bonds.

  • 30. Hussain, T.
    et al.
    Pathak, B.
    Maark, T. A.
    Ramzan, M.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Functionalization of graphane with alkali and alkaline-earth metals: An insulator-to-metallic transition2012In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 99, no 4, p. 47004-Article in journal (Refereed)
    Abstract [en]

    In view of interest in functionalized carbon nanostructures due to their potential applications in nanotechnology and nanoelectronics, we have performed a systematic and thorough density functional theory (DFT) study on the interaction of the elements in the first two groups of the periodic table with graphane (hydrogenated graphene) sheet. GGA approximation as employed in DFT has been used to study in detail the binding configuration, bond length, charge transfer and band gap of each of these adatoms doped graphane (CH) systems. To have a better understanding of the adatoms-CH interaction, different doping concentrations varying from 3.125% to 50% have been considered. A certain trend in binding strength, bond length and charge transfer has been found in the case of both alkali metal and alkaline-earth metal adatoms. In the case of alkali-metal adatoms at the low doping concentration of 3.125%, semiconductor behavior was found, whereas at doping higher than this the compound showed metallic behavior. In contrast, alkaline-earth metal-doped CH exhibited metallic behavior at all the doping concentrations.

  • 31. Hussain, Tanveer
    et al.
    Pathak, Biswarup
    Maark, Tuhina Adit
    Araujo, Carlos Moyses
    Scheicher, Ralph H.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ab initio study of lithium-doped graphane for hydrogen storage2011In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 96, no 2, p. 27013-Article in journal (Refereed)
    Abstract [en]

    Based on the first-principle density functional calculations we predict that Li-doped graphane (prehydrogenated graphene) can be a potential candidate for hydrogen storage. The calculated Li-binding energy on graphane is significantly higher than the Li bulk's cohesive energy ruling out any possibility of cluster formations in the Li-doped graphane. Our study shows that even with very low concentration (5.56%) of Li doping, the Li-graphane sheet can achieve a reasonable hydrogen storage capacity of 3.23 wt.%. The van der Waals corrected H(2) binding energies fall within the range of 0.12-0.29 eV, suitable for practical H(2) storage applications.

  • 32. Jain, Sakshi
    et al.
    Muralidharan, Sreraman
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Panigrahi, Prasanta K.
    Secure quantum conversation through non-destructive discrimination of highly entangled multipartite states2009In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 87, no 6, p. 60008-Article in journal (Refereed)
    Abstract [en]

    "Quantum conversation" is a way in which two parties can communicate classical information with each other using entanglement as a shared resource. We present this scheme using a multipartite entangled state after describing its generation through appropriate circuit diagrams. We make use of a discrimination scheme which allows one to perform a measurement on the system without destroying its entanglement. We later prove that this scheme is secure in a noiseless and a lossless quantum channel.

  • 33. Kaewmaraya, T.
    et al.
    Pathak, B.
    Araujo, C. M.
    Rosa, A. L.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Water adsorption on ZnO(10(1)over-bar0): The role of intrinsic defects2012In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 97, no 1, p. 17014-Article in journal (Refereed)
    Abstract [en]

    Density functional theory (DFT) calculations have been performed to investigate the interaction of water molecules with bare and defective ZnO(10 (1) over bar0) surfaces. We show that at high coverages water molecules avoid adsorption close to defect sites, whereas at low coverages adsorption on defective surfaces show a similar adsorption pattern to those adsorbed on the defect-free surface, adsorbing in a molecular fashion. Finally we show that the electronic structure of the defective non-polar surface is not much affected by the adsorption of water, with exception of the O-defect surfaces.

  • 34. Kaloni, T. P.
    et al.
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Schwingenschlögl, U.
    Substrate-enhanced superconductivity in Li-decorated graphene2013In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 104, no 4, p. 47013-Article in journal (Refereed)
    Abstract [en]

    We investigate the role of the substrate for the strength of the electron-phonon coupling in Li-decorated graphene. We find that the interaction with a h-BN substrate leads to a significant enhancement from lambda(0) = 0.62 to lambda(1) = 0.67, which corresponds to a 25% increase of the transition temperature from T-c0 = 10.33K to T-c1 = 12.98 K. The superconducting gaps amount to 1.56 meV (suspended) and 1.98 meV (supported). These findings open up a new route to enhanced superconducting transition temperatures in graphene-based materials by substrate engineering.

  • 35. Khrapak, S. A.
    et al.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Chaudhuri, M.
    Zobnin, A.
    Usachev, A.
    Rau, C.
    Thoma, M. H.
    Petrov, O. F.
    Fortov, V. E.
    Morfill, G. E.
    Grain charging in an intermediately collisional plasma2012In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 97, no 3, p. 35001-Article in journal (Refereed)
    Abstract [en]

    The charges of mu m-size particles in the quasineutral bulk plasma of a dc discharge are determined experimentally in a pressure range between 100 and 500 Pa, spanning the transition between the weakly collisional and highly collisional (hydrodynamic) regimes, where the ion mean free path drops below the plasma screening length. The charge is determined using the force balance condition from the measured particle drift velocities in stable particle flows. A simple interpolation formula for the ion flux to the grain in the transitional regime is shown to fit quite well the experimental results.

  • 36.
    Korenivski, Vladislav
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Iovan, Adrian
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Kadigrobov, A.
    Shekhter, R. I.
    Spin laser based on magnetic nano-contact array2013In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 104, no 2, p. 27011-Article in journal (Refereed)
    Abstract [en]

    Arrays of 10 nm diameter point contacts of exchange-coupled spin-majority/spin-minority ferromagnetic metals, integrated into infrared-terahertz range photon resonators, are fabricated and measured electrically and optically. Giant, threshold-type electronic excitations under high-current pumping of the devices are observed as abrupt but reversible steps in device resistance, in many cases in excess of 100%, which correlate with optical emission from the devices. The results are interpreted as due to stimulated spin-flip electron-photon relaxation in the system.

  • 37.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    The Superfluidity and Experimental Properties of Odd-Energy-Gap Superconductors1993In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 26, no 2Article in journal (Refereed)
  • 38.
    Li, Yunguo
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Pathak, Biswarup
    Nisar, Jawad
    Qian, Zhao
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Metal-decorated graphene oxide for ammonia adsorption2013In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 103, no 2, p. 28007-Article in journal (Refereed)
    Abstract [en]

    Based on the first-principles density functional theory, we have studied the stability, electronic structure and ammonia storage capacity of metal-decorated graphene oxide (GO). Metal atoms (Mg and Li) are bonded strongly to the epoxy oxygen atoms on the surface of the GO sheet, which can act as high-surface-area adsorbent for the ammonia uptake and release. Each metal atom can bind several ammonia molecules around itself with a reasonable binding energy. We find metal-decorated GO can store up to tens of moles of ammonia per kilogram, which is far better than the recently reported excellent ammonia adsorption by GO.

  • 39.
    Lidmar, Jack
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Wallin, Mats
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Critical properties of Bose-glass superconductors1999In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 47, no 4Article in journal (Refereed)
    Abstract [en]

    We study vortex lines in high-temperature superconductors with columnar defects produced by heavy-ion irradiation. We reconsider scaling theory for the Bose-glass transition with tilted magnetic fields, and propose, e.g. , a new scaling form for the shape of the Bose glass phase boundary, which is relevant for experiments. We also consider Monte Carlo simulations for a vortex model with a screened interaction. Critical exponents are determined from scaling analysis of Monte Carlo data for current-voltage characteristics and other quantities. The dynamic critical exponent is found to be z = 4.6 ± 0.3.

  • 40.
    Mathieu, Roland
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    He, J. P.
    Yu, X. Z.
    Kaneko, Y.
    Uchida, M.
    Lee, Y. S.
    Arima, T.
    Asamitsu, A.
    Tokura, Y.
    Coexistence of long-ranged charge and orbital order and spin-glass state in single-layered manganites with weak quenched disorder2007In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 80, no 3, p. 37001-Article in journal (Refereed)
    Abstract [en]

    The relationship between orbital and spin degrees of freedom in the single crystals of the hole-doped Pr1-xCa1+xMnO4, 0.3 <= x <= 0.7 has been investigated by means of ac-magnetometry and charge transport. We show that in an intermediate underdoped region, with 0.35 <= x < 0.5, the "orbital-master spin-slave" relationship commonly observed in half-doped manganites does not take place. The long-ranged charge-orbital order is not accompanied by an antiferromagnetic transition at low temperatures, but by a frustrated short-ranged magnetic state bringing forth a spin-glass phase. We discuss in detail the nature and origin of this true spin-glass state, which, as in the half-doped manganites with large quenched disorder, is not related to the macroscopic phase separation observed in crystals with minor defects or impurities.

  • 41. Miniotas, A.
    et al.
    Nordblad, P.
    Andersson, Magnus
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Hjorvarsson, B.
    Gadolinium trihydride - A new magnetoresistive semiconductor2002In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 58, no 3, p. 442-447Article in journal (Refereed)
    Abstract [en]

    Large negative magnetoresistance and magnetisation anomalies are found in epitaxial GdH3-delta films. The zero-field semiconductor-like behavior in the resistivity is completely suppressed at a magnetic field of 120 kOe. Temperature and field dependence of the magnetisation supports short-range ordering in the paramagnetic host, mediated by the vacancy state of trihydride.

  • 42. Montero, M. I.
    et al.
    Åkerman, Johan
    Varilci, A.
    Schuller, I. K.
    Flux pinning by regular nanostructures in Nb thin films: Magnetic vs. structural effects2003In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 63, no 1, p. 118-124Article in journal (Refereed)
    Abstract [en]

    Periodic pinning effects in indented Nb films and Nb films with rectangular arrays of submicrometric Ni dots were studied. The indented samples consisted of Nb film deposited on top of Si substrates patterned with rectangular arrays of nanoholes. Pinning effects can be observed in the evolution of resistivity and critical current with the applied magnetic field, showing the same qualitative behavior, for both types of samples. The main difference between them is that the matching effects are more pronounced in the samples with magnetic dots. The analysis and comparison of these results allows determining the pinning as due to superconductivity suppression around the nanostructures (indentations or dots) due to a thickness reduction. For the samples with magnetic dots, this suppression of superconductivity is reinforced by the magnetic proximity effect.

  • 43. Nisar, J.
    et al.
    Peng, X.
    Kang, T. W.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Stabilizing the defect-induced dilute magnetic semiconductors: Li-doping in GaN with Ga vacancies2011In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 93, no 5, p. 57006-Article in journal (Refereed)
    Abstract [en]

    By means of first-principles calculations, we have investigated the effects of various Li-doping on the exchange interaction and the formation energy in bulk GaN with Ga vacancies. Although the Ga vacancies can induce ferromagnetism in GaN, their formation energy is rather high. Our calculations show that Li-doping can effectively tune the formation energy of Ga vacancies. It is revealed that the stabilizing effect depends on whether the number of holes is increased or decreased after Li-doping. When Li atoms substitutes for N atoms or occupies the interstitial sites, the holes are reduced and the formation energy of Ga vacancies is lowered. In contrast, Li substituting for Ga generates additional holes in the system, leading to an enhancement of the formation energy of Ga vacancies and making the system less stable. Copyright (c) EPLA, 2011

  • 44. Nisar, J.
    et al.
    Peng, X.
    Kang, T. W.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Stabilizing the defect-induced dilute magnetic semiconductors: Li-doping in GaN with Ga vacancies (vol 93, 57006, 2011)2011In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 94, no 1, p. 19901-Article in journal (Refereed)
  • 45. Nisar, J.
    et al.
    Scheicher, R. H.
    Peng, X.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Stability of ferromagnetic phase in Fe-doped AlH32009In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 85, no 6Article in journal (Refereed)
    Abstract [en]

    We have carried out a systematic theoretical investigation of Fe-doped AlH3 to study its magnetic properties and to assess the stability of the ferromagnetic phase in this material. All calculations were performed using the projector augmented-wave method and generalized-gradient approximation (GGA) as well as GGA+U. The magnetic moment is found to be constant at 1.1 mu(B) per Fe-atom in the ferromagnetic configuration for distances between adjacent Fe atoms varying from 3.25 angstrom to 7.41 angstrom. We conclude that the ferromagnetic phase in Fe-doped AlH3 is stable both for near and far configurations of Fe. The stability of the ferromagnetic phase is due to the holes created by Fe-doping and the larger level splitting of the interacting gap states within the ferromagnetic phase.

  • 46.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Non-Hermitian neutrino oscillations in matter with PT symmetric Hamiltonians2016In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 113, no 6, article id 61001Article in journal (Refereed)
    Abstract [en]

    We introduce and develop a novel approach to extend the ordinary two-flavor neutrino oscillation formalism in matter using a non-Hermitian PT symmetric effective Hamiltonian. The condition of PT symmetry is weaker and less mathematical than that of hermicity, but more physical, and such an extension of the formalism can give rise to sub-leading effects in neutrino flavor transitions similar to the effects by so-called non-standard neutrino interactions. We derive the necessary conditions for the spectrum of the effective Hamiltonian to be real as well as the mappings between the fundamental and effective parameters. We find that the real spectrum of the effective Hamiltonian will depend on all new fundamental parameters introduced in the non-Hermitian PT symmetric extension of the usual neutrino oscillation formalism and that either i) the spectrum is exact and the effective leptonic mixing must always be maximal or ii) the spectrum is approximate and all new fundamental parameters must be small.

  • 47.
    Ohlsson, Tommy
    et al.
    KTH, Superseded Departments, Physics.
    Winter, Walter
    Could one find petroleum using neutrino oscillations in matter?2002In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 60, no 1, p. 34-39Article in journal (Refereed)
    Abstract [en]

    In neutrino physics, it is now widely believed that neutrino oscillations are influenced by the presence of matter, modifying the energy spectrum produced by a neutrino beam traversing the Earth. Here, we will discuss the reverse problem, i.e. what could be learned about the Earth's interior from a single neutrino baseline energy spectrum, especially about the Earth's mantle. We will use a statistical analysis with a low-energy neutrino beam under very optimistic assumptions. At the end, we will note that it is hard to find petroleum with such a method, though it is not too far away from technical feasibility.

  • 48. Plimak, L. I.
    et al.
    Stenholm, Stig Torsten
    KTH, School of Engineering Sciences (SCI), Physics.
    Operator ordering and causality beyond the rotating wave approximation2011In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 96, no 3, p. 34002-Article in journal (Refereed)
    Abstract [en]

    Conventional definition of the time-normal operator ordering (KELLEY P. L. and KLEINER W. H., Phys. Rev., 136 (1964) A316) is prone to causality violations (de HAAN M., Physica A, 132 (1985) 375; 397). We show that such violations disappear if this definition is amended outside the rotating wave approximation. Nonrelativistic causality of an arbitrary time-normal product turns out to be a property of quantum kinematics, while relativistic causality is demonstrated for a time-normal product of two operators under the most general assumptions about quantum dynamics (commutativity of operators at space-like intervals). This eliminates the key obstacle preventing phase-space techniques of quantum optics from being extended to arbitrary quantum fields including fermions.

  • 49.
    Polishchuk, Dmytr
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Tykhonenko-Polishchuk, Yu.O.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. National Academy of Sciences of Ukraine, Ukraine.
    Kravets, Anatolii
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. National Academy of Sciences of Ukraine, Ukraine.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Thermal switching of indirect interlayer exchange in magnetic multilayers2017In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 118, no 3, article id 37006Article in journal (Refereed)
    Abstract [en]

    We propose a magnetic multilayer layout, in which the indirect exchange coupling (IEC also known as RKKY) can be switched on and off by a slight change in temperature. We demonstrate such on/off IEC switching in a Fe/Cr/FeCr-based system and obtain thermal switching widths as small as 10-20 K, essentially in any desired temperature range, including at or just above room temperature. These results add a new dimension of tunable thermal control to IEC in magnetic nanostructures, highly technological in terms of available materials and operating physical regimes.

  • 50. Ramzan, M.
    et al.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ferromagnetism in the potential cathode material LiNaFePO4F2009In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 87, no 1Article in journal (Refereed)
    Abstract [en]

    We present the ab initio study of the cathode material LiNaFePO4F, which is suitable for rechargeable batteries. Our calculations reveal the ferromagnetic order to be the ground state of this material. We also predict more than 5.0V intercalation voltage of this material for sodium-ion batteries. The low cost of sodium iron. fluorophasphate batteries and more than 5.0V intercalation voltage makes it the more suitable candidate, commercially and scientifically, than any other cathode materials for rechargeable batteries.

12 1 - 50 of 65
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