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  • 1. Babaev, Egor
    et al.
    Carlstrom, J.
    Silaev, Mihail
    KTH, School of Engineering Sciences (SCI), Physics, Statistical Physics.
    Speight, J. M.
    Type-1.5 superconductivity in multicomponent systems2017In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 533, p. 20-35Article in journal (Refereed)
    Abstract [en]

    In general a superconducting state breaks multiple symmetries and, therefore, is characterized by several different coherence lengths i = 1,..., N. Moreover in multiband material even superconducting states that break only a single symmetry are nonetheless described, under certain conditions by multi component theories with multiple coherence lengths. As a result of that there can appear a state where some coherence lengths are smaller and some are larger than the magnetic field penetration length A: xi(1) <= xi(2)...<root 2 lambda < xi(M) <=... (N). That state was recently termed "type-1.5" superconductivity. This breakdown of type-1/type-2 dichotomy is rather generic near a phase transition between superconducting states with different symmetries. The examples include the transitions between U(1) and U(1) x U(1) states or between U(1) and U(1) x Z(2) states. The later example is realized in systems that feature transition between s-wave and s + is states. The extra fundamental length scales have many physical consequences. In particular in these regimes vortices can attract one another at long range but repel at shorter ranges. Such a system can form vortex clusters in low magnetic fields. The vortex clustering in the type 1.5 regime gives rise to many physical effects, ranging from macroscopic phase separation in domains of different broken symmetries, to unusual transport properties. Prepared for the proceedings of Vortex IX conference, Rhodes 12-17 September 2015.

  • 2.
    Babaev, Egor
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Statistical Physics.
    Carlström, J.
    Silaev, Mihail
    KTH, School of Engineering Sciences (SCI), Physics, Statistical Physics.
    Speight, J. M.
    Type-1.5 superconductivity2017In: Superconductors at the Nanoscale: From Basic Research to Applications, Walter de Gruyter GmbH , 2017, p. 133-164Chapter in book (Other academic)
  • 3.
    Babaev, Egor
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Carlström, Johan
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Garaud, J.
    Silaev, Mihail
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Speight, J. M.
    Type-1.5 superconductivity in multiband systems: Magnetic response, broken symmetries and microscopic theory - A brief overview2012In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 479, p. 2-14Article in journal (Refereed)
    Abstract [en]

    A conventional superconductor is described by a single complex order parameter field which has two fundamental length scales, the magnetic field penetration depth lambda and the coherence length xi. Their ratio kappa determines the response of a superconductor to an external field, sorting them into two categories as follows; type-I when kappa < 1/root 2 and type-II when kappa > 1/root 2. We overview here multicomponent systems which can possess three or more fundamental length scales and allow a separate "type-1.5" superconducting state when, e. g. in two-component case xi(1) < root 2 lambda < xi(2). In that state, as a consequence of the extra fundamental length scale, vortices attract one another at long range but repel at shorter ranges. As a consequence the system should form an additional Semi-Meissner state which properties we discuss below. In that state vortices form clusters in low magnetic fields. Inside the cluster one of the component is depleted and the superconductor-to-normal interface has negative energy. In contrast the current in second component is mostly concentrated on the cluster's boundary, making the energy of this interface positive. Here we briefly overview recent developments in Ginzburg-Landau and microscopic descriptions of this state.

  • 4.
    Babaev, Egor
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Silaev, Mihail
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Comment on "Ginzburg-Landau theory of two-band superconductors: Absence of type-1.5 superconductivity"2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 1, p. 016501-Article in journal (Other academic)
    Abstract [en]

    The recent paper by V. G. Kogan and J. Schmalian [Phys. Rev. B 83, 054515 (2011)] argues that the widely used two-component Ginzburg-Landau (GL) models are not correct, and further concludes that in the regime which is described by a GL theory there could be no disparity in the coherence lengths of two superconducting components. This would in particular imply that [in contrast to U(1) x U(1) superconductors] there could be no "type-1.5" superconducting regime in U(1) multiband systems for any finite interband coupling strength. We point out that these claims are incorrect and based on an erroneous scheme of reduction of a two-component GL theory.

  • 5.
    Babaev, Egor
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Silaev, Mihail
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Type-1.5 Superconductivity in Multiband and Other Multicomponent Systems2013In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, E-ISSN 1557-1947, Vol. 26, no 5, p. 2045-2055Article in journal (Refereed)
    Abstract [en]

    Usual superconductors are classified into two categories: of type-1 when the ratio of the magnetic field penetration length (lambda) to coherence length (xi) kappa = lambda/xi < 1/root 2 and of type-2 when kappa > 1/root 2. The boundary case kappa = 1/root 2 is also considered to be a special situation, frequently termed as "Bogomolnyi limit". Here we discuss multicomponent systems which can possess three or more fundamental length scales and allow a separate superconducting state, which was recently termed "type-1.5". In that state, a system has the following hierarchy of coherence and penetration lengths xi(1) < root 2 lambda < xi(2). We also briefly overview the works on single-component regime kappa approximate to 1/root 2 and comment on recent discussion by Brandt and Das in the proceedings of the previous conference in this series.

  • 6. Garaud, Julien
    et al.
    Silaev, Mihail
    KTH, School of Engineering Sciences (SCI), Physics, Statistical Physics.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Physics, Statistical Physics.
    Microscopically derived multi-component Ginzburg-Landau theories for s plus is superconducting state2017In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 533, p. 63-73Article in journal (Refereed)
    Abstract [en]

    Starting with the generic Ginzburg-Landau expansion from a microscopic N-band model, we focus on the case of a 3-band model which was suggested to be relevant to describe some iron-based superconductors. This can lead to the so-called s + is superconducting state that breaks time-reversal symmetry due to the competition between different pairing channels. Of particular interest in that context, is the case of an interband dominated pairing with repulsion between different bands. For that case we consider in detail the relevant reduced two-component Ginzburg-Landau theory. We provide detailed analysis of the ground state, length scales and topological properties of that model. Prepared for the proceedings of Vortex IX conference in Rhodes (Sept. 2015).

  • 7.
    Garaud, Julien
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Silaev, Mihail
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Thermoelectric Signatures of Time-Reversal Symmetry Breaking States in Multiband Superconductors2016In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 116, no 9, article id 097002Article in journal (Refereed)
    Abstract [en]

    We show that superconductors with broken time-reversal symmetry have very specific magnetic and electric responses to inhomogeneous heating. A local heating of such superconductors induces a magnetic field with a profile that is sensitive to the presence of domain walls and crystalline anisotropy of superconducting states. A nonstationary heating process produces an electric field and a charge imbalance in different bands. These effects can be measured and used to distinguish s + is and s + id superconducting states in the candidate materials such as Ba1-xKxFe2As2.

  • 8.
    Silaev, M. A.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Stable fractional flux vortices and unconventional magnetic state in two-component superconductors2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, no 14, p. 144519-Article in journal (Refereed)
    Abstract [en]

    In the framework of London theory we study the unconventional magnetic state in two-component superconductors with a finite density of fractional flux vortices stabilized near the surface. We show that the process of vortex entry into the two-component superconductor consists of several steps, while the external magnetic field increases from zero. At the first stage only vortices in one of the order parameter components penetrate and sit at the equilibrium position near the surface. When the magnetic field is increased further, vortices in the second-order parameter component eventually enter the superconductor. Such a complex partial vortex penetration leads to the modification of a Bean-Livingston barrier and a magnetization curve as compared to conventional single-component superconductors. We discuss the possibility of experimental identification of protonic superconductivity in the projected superconducting state of liquid metallic hydrogen and hydrogen-rich alloys with the help of the partial vortex penetration effect.

  • 9.
    Silaev, Mihail A.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Dissipative Vortex Motion in Fermi Superfluids at Ultra Low Temperatures2013In: Journal of Low Temperature Physics, ISSN 0022-2291, E-ISSN 1573-7357, Vol. 171, no 5-6, p. 539-550Article in journal (Refereed)
    Abstract [en]

    We discuss in detail the recently proposed mechanism of dissipation and damping of the vortex motion in Fermi superfluids at temperatures much smaller than the critical one (Silaev, Phys. Rev. Lett., 108:045303, 2012). In the absence of the heat bath of normal component the kinetic energy of the superflow is transferred to the vortex core fermions due to the accelerated vortex motion. The resulting local heating of the vortex cores creates the heat flux carried by non-equilibrium quasiparticles emitted by moving vortices. Here we study this peculiar kinetics of localized quasiparticles beyond relaxation time approximation, calculate the decrement of Kelvin waves and the total power losses in Kelvin wave cascade realized by the turbulent motion of He-3-B.

  • 10.
    Silaev, Mihail A.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Universal Mechanism of Dissipation in Fermi Superfluids at Ultralow Temperatures2012In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 108, no 4, p. 045303-Article in journal (Refereed)
    Abstract [en]

    We show that the vortex dynamics in Fermi superfluids at ultralow temperatures is governed by the local heating of the vortex cores creating the heat flux carried by nonequilibrium quasiparticles emitted by moving vortices. This mechanism provides a universal zero temperature limit of dissipation in Fermi superfluids. For the typical experimental conditions realized by the turbulent motion of He-3-B, the temperature of the vortex cores is estimated to be of the order 0.2T(c). The dispersion of Kelvin waves is derived, and the heat flow generated by Kelvin cascade is shown to have a value close to that experimentally observed.

  • 11.
    Silaev, Mihail
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Microscopic derivation of two-component Ginzburg-Landau model and conditions of its applicability in two-band systems2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 13, p. 134514-Article in journal (Refereed)
    Abstract [en]

    We report a microscopic derivation of two-component Ginzburg-Landau (GL) field theory and the conditions of its validity in two-band superconductors. We also investigate the conditions when microscopically derived or phenomenological GL models fail and one should resort to a microscopic description. We show that besides being directly applicable at elevated temperatures, a version of a minimal two-component GL theory in certain cases also gives an accurate description of certain aspects of a two-band system, even substantially far from T-c. This shows that a two-component GL model can be used for addressing a wide range of questions in multiband systems, in particular vortex physics and magnetic response. We also argue that a single Ginzburg-Landau parameter cannot in general characterize the magnetic response of multiband systems.

  • 12.
    Silaev, Mihail
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Microscopic theory of type-1.5 superconductivity in multiband systems2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 9, p. 094515-Article in journal (Refereed)
    Abstract [en]

    We report a self-consistent microscopic theory of characteristic length scales, vortex structure, and type-1.5 superconducting state in two-band systems using two-band Eilenberger formalism.

  • 13.
    Silaev, Mihail
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Unusual mechanism of vortex viscosity generated by mixed normal modes in superconductors with broken time reversal symmetry2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 22, p. 220504-Article in journal (Refereed)
    Abstract [en]

    We show that under certain conditions, multiband superconductors with broken time reversal symmetry have a vortex viscosity-generating mechanism which is different from that in conventional superconductors. It appears due to the existence of a mixed superfluid phase-density mode inside the vortex core. This contribution is dominant near the time reversal symmetry-breaking phase transition. The results could be relevant for the three-band superconductor Ba1-xKxFe2As2.

  • 14.
    Silaev, Mihail
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Statistical Physics.
    Garaud, Julien
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics. KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Phase diagram of dirty two-band superconductors and observability of impurity-induced s plus i s state2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 2, article id 024517Article in journal (Refereed)
    Abstract [en]

    We investigate the phase diagram of dirty two-band superconductors. This paper primarily focuses on the properties and observability of the time-reversal symmetry-breaking s + is superconducting states, which can be generated in two-band superconductors by interband impurity scattering. We show that such states can appear in two distinct ways. First, according to a previously discussed scenario, the s + is state can form as an intermediate phase at the impurity-driven crossover between s(+/-) and s(++) states. We show that there is a second scenario where domains of the s + is state exists in the form of an isolated dome inside the s(+/-) domain, completely detached from the transition between s(+/-) and s(++) states. We demonstrate that in both cases the s + is state generated by impurity scattering exists in an extremely small interval of impurity concentrations. Although this likely precludes direct experimental observation of the s + is state formation due to this mechanism, this physics leads to the appearance of a region inside both the s(+/-) and s(++) domains with unusual properties due to softening of normal modes.

  • 15.
    Silaev, Mihail
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Garaud, Julien
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Unconventional thermoelectric effect in superconductors that break time-reversal symmetry2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 17, article id 174510Article in journal (Refereed)
    Abstract [en]

    We demonstrate that superconductors that break time-reversal symmetry can exhibit thermoelectric properties, which are entirely different from the Ginzburg mechanism. As an example, we show that in the s + is superconducting state there is a reversible contribution to thermally induced supercurrent, whose direction is not invariant under time-reversal operation. Moreover in contrast to Ginzburg mechanism it has a singular behavior near the time-reversal symmetry breaking phase transition. The effect can be used to confirm or rule out the s + is state, which is widely expected to be realized in pnictide compounds Ba1-xKxFe2As2 and stoichiometric LiFeAs.

  • 16.
    Silaev, Mihail
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics. Aalto Univ, Finland.
    Heikkila, Tero T.
    Virtanen, Pauli
    Lindblad-equation approach for the full counting statistics of work and heat in driven quantum systems2014In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 90, no 2, p. 022103-Article in journal (Refereed)
    Abstract [en]

    We formulate the general approach based on the Lindblad equation to calculate the full counting statistics of work and heat produced by driven quantum systems weakly coupled with a Markovian thermal bath. The approach can be applied to a wide class of dissipative quantum systems driven by an arbitrary force protocol. We show the validity of general fluctuation relations and consider several generic examples. The possibilities of using calorimetric measurements to test the presence of coherence and entanglement in the open quantum systems are discussed.

  • 17.
    Silaev, Mihail
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Statistical Physics.
    Vargunin, Artjom
    Vortex motion and flux-flow resistivity in dirty multiband superconductors2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 22, article id 224506Article in journal (Refereed)
    Abstract [en]

    The conductivity of vortex lattices in multiband superconductors with high concentration of impurities is calculated based on microscopic kinetic theory at temperatures significantly smaller than the critical one. Both the limits of high and low fields are considered, when the magnetic induction is close to or much smaller than the critical field strength IIc2, respectively. It is shown that in contrast to single-band superconductors, the resistive properties are not universal but depend on the pairing constants and ratios of diffusivities in different bands. The low-field magnetoresistance can strongly exceed the Bardeen-Stephen estimation in a quantitative agreement with experimental data for the two-band superconductor MgB2.

  • 18.
    Silaev, Mihail
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics. Aalto University, Finland.
    Virtanen, P.
    Bergeret, F. S.
    Heikkila, T. T.
    Long-Range Spin Accumulation from Heat Injection in Mesoscopic Superconductors with Zeeman Splitting2015In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 114, no 16, article id 167002Article in journal (Refereed)
    Abstract [en]

    We describe far-from-equilibrium nonlocal transport in a diffusive superconducting wire with a Zeeman splitting, taking into account different spin relaxation mechanisms. We demonstrate that due to the Zeeman splitting, an injection of current in a superconducting wire creates spin accumulation that can only relax via thermalization. This effect leads to a long-range spin accumulation detectable in the nonlocal signal. Our model gives a qualitative explanation and provides accurate fits of recent experimental results in terms of realistic parameters.

  • 19.
    Silaev, Mihail
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics. Aalto Univ, OV Lounasmaa Lab, Finland.
    Virtanen, P.
    Heikkila, T. T.
    Bergeret, F. S.
    Spin Hanle effect in mesoscopic superconductors2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 2, p. 024506-Article in journal (Refereed)
    Abstract [en]

    We present a theoretical study of spin transport in a superconducting mesoscopic spin valve under the action of a magnetic field misaligned with respect to the injected spin. We demonstrate that superconductivity can either strongly enhance or suppress the coherent spin rotation, depending on the type of spin relaxation mechanism being dominated either by spin-orbit coupling or spin-flip scattering at impurities. We also predict a subgap contribution to the nonlocal conductance in multiterminal superconducting hybrid structures which completely eliminates the effect of spin rotation at sufficiently low temperatures.

  • 20.
    Silaev, Mikhail
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Magnetic behavior of dirty multiband superconductors near the upper critical field2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 21, article id 214509Article in journal (Refereed)
    Abstract [en]

    Magnetic properties of dirty multiband superconductors near the upper critical field are studied. The parameter kappa(2) characterizing magnetization slope is shown to have a significant temperature variation which is quite sensitive to the pairing interactions and relative strengths of intraband impurity scattering. In contrast to single-band superconductors the increase of kappa(2) at low temperatures can be arbitrarily large determined by the ratio of maximal and minimal diffusion coefficients in different bands. Temperature dependencies of kappa(2)(T) in two-band MgB2 and iron-based superconductors are shown to be much more sensitive to the multiband effects than the upper critical field H-c2(T).

  • 21.
    Silaev, Mikhail A.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Thuneberg, E. V.
    Fogelstrom, M.
    Lifshitz Transition in the Double-Core Vortex in He-3-B2015In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 115, no 23, article id 235301Article in journal (Refereed)
    Abstract [en]

    We study the spectrum of fermion states localized within the vortex core of a weak-coupling p-wave superfluid. The low energy spectrum consists of two anomalous branches that generate a large density of states at the locations of the half cores of the vortex. Fermi liquid interactions significantly stretch the vortex structure, which leads to a Lifshitz transition in the effective Fermi surface of the vortex core fermions. We apply the results to the rotational dynamics of vortices in superfluid He-3-B and find an explanation for the observed slow mode.

1 - 21 of 21
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