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  • 1. Ambrosch-Draxl, C.
    et al.
    Korzhavyi, Pavel A.
    Uppsala University.
    Johansson, Börje
    Uppsala University.
    First-principles study of oxygen ordering in YBa2Cu3O7-x2000Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 341, s. 1997-1998Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have performed first-principles calculations considering different patterns of oxygen/vacancy ordering in the Cu-O chains of YBa2Cu3O7-x. From the total-energy values we determine the effective interactions of the oxygen atoms within the basal plane by using the cluster expansion technique. Furthermore, we discuss the effect of ordering to the density of states at the Fermi level.

  • 2.
    Andersson, Magnus
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Eltsev, Yuri
    KTH, Tidigare Institutioner, Fysik.
    Lundqvist, Björn
    KTH, Tidigare Institutioner, Fysik.
    Rydh, Andreas
    KTH, Tidigare Institutioner, Fysik.
    Rapp, Östen
    KTH, Tidigare Institutioner, Fysik.
    Vortex liquid properties in optimally doped and oxygen-deficient YBa2Cu3O7-delta single crystals2000Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 332, nr 1-4, s. 86-92Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electrical anisotropy, gamma = (m(c)/m(ab))(1/2), can easily be varied by changing the oxygen content in single crystals of YBa2Cu3O7-delta (YBCO); thus making this system useful as a test system For vortex dynamics in high-temperature superconductors (HTSC). Here, some recent results are reviewed. Measurements of the c-axis resistivity with the magnetic field B II ab-plane is shown to be a powerful tool in studying vortex velocity correlations both parallel and perpendicular to the applied field. In optimally doped crystals, we iind evidence that the in-plane vortex lattice melts at T-m into a disentangled vortex liquid, which looses its correlation along the c-axis at a higher temperature T-br > T-m. For weakly disordered crystals and magnetic fields B \\ c-axis, a relation between the vortex glass line and the magnetic field dependence of the characteristic energy, U*, in the pinned vortex liquid is proposed. This approach is shown to give support to our idea of describing the vortex glass resistivity in the liquid regime by a modified glass correlation Length, xi(g) = xi(0)\k(B)T/U-0 - 1\(-nu) which depends on the average pinning energy, Lr,, in the system [A. Rydh, O. Rapp, M. Andersson, Phys. Rev. Lett. 83 (1999) 1850].

  • 3.
    Andersson, Magnus
    et al.
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Fivat, Patrice
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Obara, Haruhiko
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Fabrega, Lourdes
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Triscone, Jean-Marc
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Decroux, Michel
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Fischer, Oystein
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    H-T PHASE-DIAGRAM OF DYBA2CU3O7-DELTA(Y0.45PR0.55)BA2CU3O7-DELTA MULTILAYERS IN THE MIXED-STATE1994Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 235, s. 2617-2618Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    From measurements of I-V characteristics of DyBa2Cu3O7-delta/(Y0.45Pr0.55)Ba2Cu3O7.delta multilayers, we have experimentally determined the characteristic temperature separating the vortex liquid from the vortex solid. We suggest that the cross-over temperature is determined by the anisotropy given by the artificially layered structure of these multilayers and that the studied system can be used as a test system for vortex dynamics.

  • 4.
    Andersson, Magnus
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Hegedüs, Zsolt
    Arrheniuslaboratoriet, Stockholms Universitet.
    Nygren, Mats
    Arrheniuslaboratoriet, Stockholms Universitet.
    Rapp, Östen
    KTH, Tidigare Institutioner, Fysik.
    STRUCTURAL, THERMAL AND ELECTRICAL STUDIES OF THE Y1-2XCAXTHXBA2CU3O7-DELTA SYSTEM WITH 0 LESS-THAN-OR-EQUAL-TO 0.201989Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 160, nr 1, s. 65-68Artikkel i tidsskrift (Fagfellevurdert)
  • 5.
    Andersson, Magnus
    et al.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Lundqvist, Björn
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Rapp, Östen
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Vortex liquid-to-solid transition in underdoped YBa2Cu3O7-delta single crystals with B parallel to ab2003Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 388, s. 691-692Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A nearly magnetic field independent vortex liquid-to-solid transition has been observed in both the ab-plane and in the c-axis resistivity of underdoped YBa2Cu3O7-delta single crystals for magnetic fields Bparallel toab-plane. These observations suggest that intrinsic pinning caused by the superconducting layers do neither lead to a system of completely decoupled superconducting layers nor to a smectic vortex phase at high fields. A possible explanation may include a transition driven by changes in elastic properties (e.g., the shear modulus) of the vortex system.

  • 6.
    Andersson, Magnus
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Rapp, Östen
    KTH, Tidigare Institutioner, Fysik.
    MAGNETORESISTANCE MEASUREMENTS ON (CA,TH)-DOPED YBA2CU3O7-DELTA1991Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 185, s. 1901-1902Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Magnetoresistance measurements on sintered Y1-2xCaxThxBa2Cu3O7-delta samples with x < = 0.1 are reported. By fitting the measured data to the Hikami-Larkin theory, we obtain coherence lengths, xi-ab and xi-c’ and a phase breaking time tau-phi All these parameters are found to decrease with (Ca,Th) doping. We also conclude that magnetoresistance measurements are highly sensitive to inhomogeneities in the sample.

  • 7.
    Andersson, Magnus
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Rapp, Östen
    KTH, Tidigare Institutioner, Fysik.
    UPPER CRITICAL MAGNETIC-FIELD OF Y1-2XCAXTHXBA2CU3O7-DELTA1989Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 162, s. 725-726Artikkel i tidsskrift (Fagfellevurdert)
  • 8.
    Andersson, Magnus
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Rapp, Östen
    KTH, Tidigare Institutioner, Fysik.
    Hegedüs, Zsolt
    Arrheniuslaboratoriet, Stockholms Universitet.
    Wen, TL
    Arrheniuslaboratoriet, Stockholms Universitet.
    Nygren, Mats
    Arrheniuslaboratoriet, Stockholms Universitet.
    STRUCTURAL AND SUPERCONDUCTING PROPERTIES OF Y1-2XCAXPRXBA2CU3O7-GAMMA1992Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 190, nr 3, s. 255-260Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Samples of the nominal composition Y1-2xCaxPrxBa2Cu3O7-delta with 0 less-than-or-equal-to x less-than-or-equal-to 0.4 have been studied by X-ray diffraction techniques, chemical analyses, and measurements of the super conducting transition temperature and the upper critical magnetic field. For x less-than-or-equal-to 0.25, the results indicate that Ca and Pr can both replace Y in agreement with the nominal composition, while for x > 0.25 only Pr enters the orthorhombic unit cell. Compared to Pr substitution in 1:2:3 we observe small changes in the depression of T(c) and strong changes in the critical field slopes. These results suggest that if Pr has a magnetic pair-breaking effect, it is close to being temperature independent.

  • 9.
    Andersson, Magnus
    et al.
    KTH, Tidigare Institutioner (före 2005), Fysik.
    Rapp, Östen
    KTH, Tidigare Institutioner (före 2005), Fysik.
    Tellgren, Roland
    Institutet för kemi, Uppsala Universitet.
    Neutron-diffraction studies of Ca-Pr doped YBa2Cu307-delta1993Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 205, nr 1-2, s. 105-110Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have performed neutron powder diffraction on samples in a series Y1-2xCaxPrxBa2Cu3O7-delta, with x=0.0, 0.1 and 0.2, and analyzed the data with the Rietveld refinement method. Small changes were observed in atomic bond distances when the amount of Ca-Pr was increased. In general, these changes could qualitatively be viewed as the sum of effects from the Ca and Pr substitutions in YBa2Cu3O7-delta samples. Analyses of the distance between the superconducting CuO2 Planes suggest that the Pr ions in the Ca-Pr substituted samples have an effective valence close to + 4.

  • 10.
    Andersson, Magnus
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Rapp, Östen
    KTH, Tidigare Institutioner, Fysik.
    Tellgren, Roland
    Institutet för kemi, Uppsala Universitet.
    NEUTRON-DIFFRACTION STUDIES OF Y1-2XCAXTHXBA2CU3O7-DELTA WITH X-LESS-THAN=0.11991Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 185, s. 915-916Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have made Rietveld refinements on neutron powder diffraction data from Y1-2xCaxThxBa2Cu3O7-delta samples with x < = 0.1. Only small changes in lattice distances are detected. Most noticeable are a flattening of the CuO-planes and a possible small increase in the distance between Cu(1) and the edge oxygen O(4). A comparison with the Y1-xCaxBa2Cu3O7-delta system is made.

  • 11.
    Andersson, Magnus
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Rydh, Andreas
    KTH, Tidigare Institutioner, Fysik.
    Rapp, Östen
    KTH, Tidigare Institutioner, Fysik.
    Vortex liquid resistivity in disordered YBa2Cu3O7-delta single crystals2000Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 341, s. 1239-1240Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The vortex solid-to-liquid transition line, T-g(B) and the linear resistivity in the vortex liquid of an optimally doped disordered YBa2Cu3O7-delta Single crystal is analyzed in detail. Our previously proposed description [Rydh, Rapp and Andersson, Phys.Rev.Lett. 83 (1999) 1850] is shown to quantitatively describe both T-g(B) and the vortex liquid resistivity above T-g using the same parameters. Furthermore, a comparison with the thermally activated behaviour usually employed to account for the resistivity in the vortex liquid is reported.

  • 12. Artemov, A. N.
    et al.
    Drobotko, V. F.
    Grishin, Alexander M.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Khokhlov, V. A.
    Kosse, A. I.
    Levchenko, G. G.
    Medvedev, Y. V.
    Prokhorov, A. Y.
    Large effect of thermal processes on the susceptibility of YBCO film with transport current2004Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 403, nr 3, s. 157-162Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The response of YBCO film with transport current to the weak alternating magnetic field was studied. The hysteresis of the temperature dependences of the response measured under cooling and heating was revealed. The qualitative explanation of this phenomenon is proposed. It is based on the fact that under certain conditions the superconductor with transport current has two steady states. It is found that the hysteresis arises only if transport current exceeds some finite value I-0.

  • 13. Babaev, Egor
    Vortices carrying an arbitrary fraction of magnetic flux quantum, neutral superfluidity and knotted solitons in two-gap Ginzburg-Landau model2004Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 404, nr 04-jan, s. 39-43Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We show that in two-gap superconductors there exist vortices which carry an arbitrary fraction of magnetic flux quantum and in two dimensions under certain conditions these vortices undergo a BKT transition which marks onset of quasi-long-range order only in a difference of phases of the two order parameters. In the second part of the talk we show that an U(1) x U(1) Ginzburg-Landau model or a GL model where U(1) x U(1) symmetry is weakly broken to U(1) is exactly equivalent to a version of the Faddeev's the nonlinear O(3) sigma model. This implies in particular that such a system possesses a hidden O(3) symmetry and besides that allows for the formation of knotted solitons. The second part of the talk is based on a joint work with L.D. Faddeev and A. Niem: Phys. Rev. B 65 (2002) 100512.

  • 14. Babaev, Egor
    et al.
    Carlstrom, J.
    Silaev, Mihail
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Statistisk fysik.
    Speight, J. M.
    Type-1.5 superconductivity in multicomponent systems2017Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 533, s. 20-35Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 15.
    Babaev, Egor
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Carlström, Johan
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Type-1.5 superconductivity in two-band systems2010Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 470, nr 19, s. 717-721Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the usual Ginzburg-Landau theory the critical value of Ginzburg-Landau parameter kappa(c) = 1/root 2 separates regimes of type-I and type-II superconductivity. The latter regime possess thermodynamically stable vortex excitations which interact with each other repulsively and tend to form vortex lattices. It was shown in [5] that this dichotomy in broken in U(1) x U(1) Ginzburg-Landau models which possess a distinct phase with vortex excitations which interact attractively at large length scales and repulsively at shorter distances. Here we discuss the influence of the Josephson coupling and that similar kind of superconductivity can also arise for entirely different reasons in superconductors where only one band is superconducting if this band interacting via a proximity effect with another band (the report is partially based on [1]).

  • 16.
    Babaev, Egor
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Carlström, Johan
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Garaud, J.
    Silaev, Mihail
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Speight, J. M.
    Type-1.5 superconductivity in multiband systems: Magnetic response, broken symmetries and microscopic theory - A brief overview2012Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 479, s. 2-14Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 17. BERNHOFF, H
    et al.
    QVARFORD, M
    SODERHOLM, S
    FLODSTROM, AS
    ANDERSEN, JN
    NYHOLM, R
    KARLSSON, Ulf O
    KTH, Skolan för informations- och kommunikationsteknik (ICT).
    LINDAU, I
    ELECTRONIC AND STRUCTURAL-PROPERTIES OF THE CU-BI2CASR2CU2O8 INTERFACE1991Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 180, nr 1-4, s. 120-123Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The formation of the Cu-Bi2CaSr2Cu2O8 interface has been studied by photoelectron spectroscopy using synchrotron radiation. Photon energies in the range 20-1000 eV were utilized in order to probe both the valence band and to monitor chemical changes upon Cu deposition, as revealed by the core-level shifts. A strong chemical reaction between Bi2CaSr2CuO8 and Cu is manifested by the formation of metallic Bi. From the intensity variations as a function of electron emission angle it is shown that the metallic Bi segregates to the top surface layer.

  • 18. BERNHOFF, H
    et al.
    QVARFORD, M
    SODERHOLM, S
    NYHOLM, R
    KARLSSON, Ulf O
    KTH, Skolan för informations- och kommunikationsteknik (ICT).
    LINDAU, I
    FLODSTROM, AS
    PHOTOEMISSION-STUDY OF THE BI2CASR2CU2O8 SUPERCONDUCTOR WITH CU, AG AND AU OVERLAYERS1993Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 218, nr 1-2, s. 103-108Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we present a photoemission study of the interaction of Cu, Ag and Au with clean single-crystal Bi2CaSr2Cu2O8 superconductor surfaces. Both the valence-band and the Bi 5d, O 1 s and Sr 3d core levels were monitored for all overlayers. Cu, Ag and Au were deposited as consecutively thicker layers starting with a third of a monolayer and progressing in steps up to a deposition in the range of eight monolayers. Comparing the results for the different overlayers reveals the Ag overlayer to be less reactive than Au which causes the formation of metallic Bi on cleaved Bi2CaSr2Cu2O8 surface. Cu is shown to be the most reactive of the three metals. The Au and Ag overlayers display an island-growth mode, while Cu grows in a layer-by-layer fashion.

  • 19. Bjornangen, T.
    et al.
    Axnas, J.
    Eltsev, Y.
    Rapp, Östen.
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    In-plane anisotropy and chain contribution from the magnetoresistivity of YBa2Cu3O7-delta2000Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 341, s. 1885-1886Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Magnetoresistivity measurements were made in untwinned YBa2Cu3O7-delta above T-c for B\\c and B\\ab, with I\\a or b. A fluctuation theory that allows for an in-plane coherence length anisotropy (gamma = xi (b)/xi (a)) was used to determine gamma. The contribution to the magnetoconductivity from the CuO-chains was also analyzed.

  • 20. Bjornangen, T.
    et al.
    Rydh, A.
    Rapp, Östen.
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Vortex liquid and solid correlation in untwinned YBa2Cu3O7-delta2003Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 388, s. 727-728Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Longitudinal- and inter-vortex correlations in an untwinned YBa2Cu3O7-delta single crystal were studied in the liquid and driven solid state, using a modified, symmetric pseudo-flux transformer method. The response of the flowing vortex system below T-m was significantly different along the field (Hparallel toa) and perpendicular to it (Hparallel toc), with both cases probed by an in-plane current mainly parallel to b.

  • 21.
    Björnängen, Therese
    et al.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Fors, Rickard
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Eltsev, Yurii
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Rapp, Östen
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Vortex correlation parallel in underdoped and perpendicular to H vertical bar vertical bar ab YBa2Cu3O7-delta2004Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 408-10, s. 564-565Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Vortex correlation in the region of the depinning transition has been studied in twinned YBa2Cu3O7-delta single crystals with T-c approximate to 80 K. Transport properties along the e-axis were performed in magnetic fields parallel to the ab-plane, using the pseudo flux-transformer method. By rotating the sample around the c-axis, both longitudinal and transverse vortex correlation could be studied. Compared to optimally doped samples, transverse vortex velocity correlation was enhanced at high fields, while longitudinal correlation remained qualitatively the same.

  • 22.
    Edström, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Three and four-body intervortex forces in the Ginzburg-Landau model of single- and multicomponent superconductivity2013Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 487, s. 19-26Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A systematic numerical study of non-pairwise vortex interaction forces in the Ginzburg-Landau model for single-and multicomponent superconductivity is presented. The interactions are obtained by highly accurate numerical free energy minimization. In particular a three-body interaction is defined as the difference between the total interaction and sum of pairwise interactions in a system of three vortices and such interactions are studied for single and two-component type-1, type-2, and type-1.5 superconductors. In the investigated regimes, the three-body inter action is found to be short-range repulsive but long-range attractive in the type-1 case, zero in the critical kappa (Bogomoln'y) case, attractive in the type-2 case and repulsive in the type-1.5 case. Some systems of four vortices are also studied and results indicate that four-body forces are of substantially less significance than the three-body interactions.

  • 23.
    Espinosa-Arronte, Beatriz
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Djupmyr, Märit
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Andersson, Magnus
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Scaling of the B-dependent resistivity for different orientations in Fe doped YBa2Cu3O7-[delta]2005Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 423, nr 1-2, s. 69-73Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The angular dependence of a previously proposed modified model of the vortex glass transition has been investigated. The in-plane resistivity in an optimally oxygen doped YBa2Cu3O7-delta single crystal, doped with 1% Fe, was measured in fields up to 12 T applied with different orientations with respect to the crystallographic c-axis. The transition curves at all orientations were successfully scaled into one curve according to a scaling variable for the normalized resistivity. Characteristic parameters of the model, like the glass transition temperature and the magnetic field B-0, were measured at each orientation and were in good agreement with the expected values. These results show that the model proposed is valid also for fields applied outside the c-axis, giving further support to a more consistent description of the vortex liquid resistivity.

  • 24.
    Espinosa-Arronte, Beatriz
    et al.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Rapp, Östen
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Andersson, Magnus
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Scaling of the vortex liquid c-axis resistivity in underdoped YBa2Cu3O7-[delta]2004Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 408, s. 583-584Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

     The c-axis resistivity was measured in a twinned, underdoped YBa2Cu3O7-delta (YBCO) single crystal with T-c = 82.2 K. Resistive transition curves for fields Lip to 12 T applied along the c-axis were scaled to one function giving a good scaling. The scaling variable is the same as for the ab resistivity in optimally doped and underdoped YBCO single crystals [Phys. Rev. B 63 (2001) 184511]. This result provides further support to a coherent description of the vortex-liquid resistivity.

  • 25. Fiolhais, Miguel C. N.
    et al.
    Essén, Hanno
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Magnetic field expulsion from an infinite cylindrical superconductor2014Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 497, s. 54-57Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The solutions of the London equations for the magnetic field expulsion from superconductors are presented in this paper for the cylindrical symmetry. The result is analyzed in detail and represented numerically for the case of a uniform external magnetic field in the transverse plane. In particular, several contour plots of the magnetic energy density are depicted for the regions inside and around the superconducting area for a wide range of penetration lengths, showing how the expulsion and penetration of the magnetic field evolve with the ratio between the penetration length and the cylinder radius.

  • 26.
    Fivat, Patrice
    et al.
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Triscone, Jean-Marc
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Andersson, Magnus
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Obara, Haruhiko
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Fischer, Oystein
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Possible entanglement of the vortices in dyba2cu3O7 (y1-xprx)ba2cu3O7 coupled heterostructure1994Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 235, s. 2599-2600Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Thermally activated flux motion is studied in proximity coupled multilayers, containing a number N of 24 Angstrom thick DyBa2Cu3O7 layers separated by 96 Angstrom (or more) of(Y1-xPrx)Ba2Cu3O7 alloy (x=0.4, x=0.55). In contrast to ultra-thin decoupled layers, for which we find that the activation energy for flux motion U approximate to=logB (H//c), coupled samples show a cross-over to a power law behaviour U approximate to B–0.5 at magnetic field H*. This characteristic field depends on the anisotropy and decreases as N increases, a behaviour which can be understood in terms of the entanglement of the vortices, resulting in a relative increase of U due to the flux line crossing energy.

  • 27. Garaud, Julien
    et al.
    Silaev, Mihail
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Statistisk fysik.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Statistisk fysik.
    Microscopically derived multi-component Ginzburg-Landau theories for s plus is superconducting state2017Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 533, s. 63-73Artikkel i tidsskrift (Fagfellevurdert)
    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).

  • 28. Ghorbani, S. R.
    et al.
    Andersson, Magnus
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Materialfysik, MF.
    Rapp, Ö.
    The normal state Hall effect in Nd1-2xCaxMxBa2Cu3O7-delta (M = Pr, Th): Evidence for hole localization by disorder2005Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 424, nr 04-mar, s. 159-168Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The transport properties of sintered samples of Nd1-2xCaxMxBa2Cu3O7-delta (M = Pr, Th) with 0 <= x <= 0.10 have been studied in the normal state by Hall effect measurements. The Hall coefficient at high temperature was almost constant for Ca-Pr while it increased with increasing Ca-Th doping concentration. The results for the Hall coefficient as a function of temperature and doping concentration were analyzed within two different models. A good agreement between models and data was obtained. On the basis of these models, it was inferred that Ca-Pr and Ca-Th doping introduce electronic disorder in the CUO2 planes. The localization tendency is driven by electronic disorder. This is the main reason for strong depression of the superconducting critical temperature in both alloys. It was found that the Hall angle is proportional to T-2 in the whole measured temperature range in Ca-Pr doped samples while there are deviations at high temperature in the Ca-Th doped series. In a phenomenological narrow band model, the conduction band was asymmetric for the pure sample and this asymmetry decreased with increasing Ca-Th doping while it was almost constant for Ca-Pr doped samples.

  • 29. Ghorbani, S. R.
    et al.
    Rapp, Östen.
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    An anomalous dip in thermoelectric power of Nd1-xPrxBa2Cu3O7-delta2003Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 388, s. 351-352Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermoelectric power, S, has been studied for sintered samples of Nd1-xPrxBa2Cu3O7-delta with 0 less than or equal to x less than or equal to 0.30 in the temperature range from the superconducting T-c to room temperature. S increases with decreasing temperature,and has a broad maximum at T-max in the region around 120 K before decreasing strongly when T-e is approached. Several properties indicate a decrease of charge concentration with increasing doping, x, from S(x, 290 K), T-max, and the resistivity rho(x, 290 K). An anomaly has been observed in S(T) for x greater than or equal to 0.20 in the form of a dip at 78 K of order 15% of S. The origin of this feature is not known.

  • 30.
    Ghorbani, Shaban Reza
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Andersson, Magnus
    KTH, Tidigare Institutioner, Fysik.
    Lundqvist, Pieter
    KTH, Tidigare Institutioner, Fysik.
    Valldor, M.
    Arrheniuslaboratoriet, Stockholms Universitet.
    Rapp, Östen
    KTH, Tidigare Institutioner, Fysik.
    Thermoelectric power and resistivity of Nd1-xCaxBa2Cu3Oy and Nd1-xLaxBa2Cu3Oy2000Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 339, nr 4, s. 245-252Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The structural and transport properties of Nd1-xCaxBa2Cu3Oy (x = 0.0, 0.03, 0.06, and 0.10) and Nd1-xLax- Ba2Cu3Oy. (x nominally 0.0, 0.05, 0.10, and 0.15) have been studied by X-ray powder diffraction, electrical resistivity, and thermoelectric power measurements. In both series, the a- and b-axis lattice parameters decrease with increasing doping while the c-axis lattice parameter increases. The transport properties suggest improved metallic behaviour with increasing Ca doping in contrast to La doping. An anomalous sharp peak in the thermoelectric power close to T-c was observed, which depended on the doping content. We analysed the thermoelectric power as a function of temperature with a two-band model with an additional linear T term. An excellent agreement between model and data was obtained.

  • 31.
    Ghorbani, Shaban Reza
    et al.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Andersson, Magnus
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Rapp, Östen
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Normal state Hall effect in Nd1-xCaxBa2Cu3O7-delta: competition between added charge and disorder2003Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 390, nr 2, s. 160-166Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The transport properties of sintered samples of Nd1-xCaxBa2CU3O7-delta with 0 less than or equal to x less than or equal to 0.20 have been studied in the normal state by Hall resistivity measurements. The Hall coefficient, R-H(x, T) was well described in terms of two different models. In a phenomenological narrow band model, the conduction band width became narrower with increasing Ca concentration while the density of states band width decreased slightly. A competition between two effects (i) added charge, and (ii) disorder introduced into the CuO2 planes by doping, could be the main reason for the observed small decrease of the band widths. In the Anderson model, the temperature dependent part of the Hall angle was independent of hole concentration and disorder while the temperature independent part increased linearly with increasing Ca content. The results in both models support that Ca introduces disorder in the CuO2 planes.

  • 32.
    Ghorbani, Shaban Reza
    et al.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Lundqvist, Pieter
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Andersson, Magnus
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Valldor, M.
    Rapp, Östen
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Thermoelectric power and resistivity of Nd1-xPrxBa2Cu3O7-delta2001Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 353, nr 1-2, s. 77-84Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The structural and transport properties of Nd1-xPrxBa2Cu3O7-delta (x = 0.0, 0.05, 0.10, and 0.15), have been studied by X-ray powder diffraction, electrical resistivity measurements, and thermoelectric power measurements. The decrease of the superconducting critical temperature with doping is described by a parabolic term and a linear term. The c-axis lattice parameter and the cell volume decrease with doping up to x = 0.10. Analyses of the thermoelectric power, critical temperature, c-axis lattice parameter, and the cell volume suggest that the Pr ions have a valence close to +4 at low doping concentration. The room temperature resistivity indicates that hole concentration decreases with increasing Pr doping. The room temperature thermoelectric power is positive for all samples and increases with increasing Pr doping due to a decrease in the carrier concentration. We analyzed the thermoelectric power as a function of temperature with a two-band model with an additional linear T term. An excellent agreement between model and data was obtained. The band width of the narrow band increases and its peak position moves away from the Fermi energy with increasing doping concentration.

  • 33.
    Grivel, Jean-Claude
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Eltsev, Yuri
    KTH, Tidigare Institutioner, Fysik.
    Andersson, Magnus
    KTH, Tidigare Institutioner, Fysik.
    Rapp, Östen
    KTH, Tidigare Institutioner, Fysik.
    Erb, Andreas
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Walker, Eric
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Flükiger, René
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    First-order melting transition observed from resistivity measurements in ultra-pure YBa2Cu3O7-delta single crystals with high twin boundary density1999Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 322, nr 3-4, s. 203-208Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    R(T) measurements have been performed on optimally and overdoped heavily twinned high-purity YBa2Cu3O7-delta single crystals, under a magnetic field B oriented parallel to the twin boundary planes (B parallel to c). The characteristic feature attributed to the flux line lattice melting transition has been observed in the overdoped case for B greater than or equal to 5 T. The first-order transition was not found in the optimally doped sample, even when B was tilted with respect to the c-axis. Differences between these samples are discussed.

  • 34. Han, S. H.
    et al.
    Lundqvist, B.
    Eltsev, Y.
    Rapp, Östen.
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Studies of dynamic critical behaviour in YBa2Cu3O7-delta single crystals2000Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 341, s. 1855-1856Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Up to now, the value of the dynamic critical exponent z is still an open question. We have studied this exponent in the intermediate (XY) critical regime in zero field for a set of high quality YBa2Cu3O7-delta Single crystals in terms of Fisher-Fisher-Huse (FFH) dynamic scaling, and using previously obtained values for the critical exponents cu of the de critical conductivity fluctuations. In this regime (i.e. the absence of Coulomb interactions), one would expect model-E dynamics (z = 1.5) to apply with the conserved charge-density conjugate to the phase fluctuations. However, we find the dynamic critical exponent to be z = 2, which is in agreement with the suggestion of FFH that due to plasma fluctuations, fully relaxational dynamics, model A (z = 2), should be appropriate.

  • 35.
    Han, Shunhui
    et al.
    KTH, Tidigare Institutioner, Fysik. KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Axnäs, Johan
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Zhao, B R
    Rapp, Östen
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Fluctuation conductivity at high temperatures in polycrystalline Hg, Tl-1223 - Is there ID fluctuation behavior?2004Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 408, s. 679-680Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Detailed resistivity measurements were made for polycrystalline Hg1-xTlxBa2Ca2Cu3O8+delta (x = 0.2) in zero field and in the temperature region from zero resistance up to 300 K. The fluctuation conductivity Deltasigma was analyzed as a function of is an element of equivalent to In(T/Tc-mf) in the range -5.5 < Inc < -0.5. 1D behavior Of fluctuation conductivity was found at high temperatures (above the 2D regime) with a crossover temperature T-1*, above which the critical exponent was found to be -1.5.

  • 36.
    Han, Shunhui
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Hegedüs, Zsolt
    Arrheniuslaboratoriet, Stockholms Universitet.
    Andersson, Magnus
    KTH, Tidigare Institutioner, Fysik.
    Nygren, Mats
    Arrheniuslaboratoriet, Stockholms Universitet.
    Rapp, Östen
    KTH, Tidigare Institutioner, Fysik.
    Yan, Y.F.
    Dept. Physics, Chinese Academy of Sciences, Beijing.
    Chen, Q.
    Dept. Physics, Chinese Academy of Sciences, Beijing.
    Wei, Y.N.
    Dept. Physics, Chinese Academy of Sciences, Beijing.
    He, Y.S.
    Dept. Solid state physics, Quinghua University, Beijing.
    Study of upper critical field Hc2(T) in doped Bi-Sr-Ca-Cu-O superconductors with 100 K phase1990Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 169, nr 3-4, s. 250-256Artikkel i tidsskrift (Fagfellevurdert)
  • 37.
    Haviland, David B.
    et al.
    KTH, Tidigare Institutioner                               , Fysik.
    Andersson, K.
    Agren, P.
    Johansson, J.
    Schollmann, V.
    Watanabe, M.
    Quantum phase transition in one-dimensional Josephson junction arrays2001Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 352, nr 04-jan, s. 55-60Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We describe experiments on one-dimensional arrays of small capacitance Josephson junctions which show how the Coulomb blockade of Cooper pair tunneling is influenced by changing the Josephson coupling energy in situ with an externally applied magnetic flux. We show how the zero bias resistance of the array is affected by the length of the array, and we use the length scaling of this resistance to infer that a quantum phase transition occurs as the Josephson coupling energy is changed. The data are qualitatively analyzed in terms of a theoretical model of the quantum phase transition which uses a mapping to the two-dimensional XY model.

  • 38. Jukna, A
    et al.
    Yun, S H
    Balevicius, S
    Karlsson, Ulf O
    KTH, Skolan för informations- och kommunikationsteknik (ICT).
    Electric properties of planar Ag/HgBa2CaCu2O6+delta interface1999Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 316, nr 1-2, s. 83-88Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Silver coatings were magnetron sputtered onto the surface of highly c-axis-oriented HgBa2CaCu2O6+delta superconducting thin films exhibiting zero resistance T-c at about 120 K and the critical current density similar to 10(5) A/cm(2) at 100 K. Electrical resistance of the Ag/HgBa2CaCu2O6+delta planar interface and current-voltage dependencies were investigated in a course of post-deposition annealing of the Ag/HgBa2CaCu2O6+delta at 50-350 degrees C in both purl oxygen and oxygen-free ambient. Results of the electrical measurements are explained in terms of the insulating layer formation at the Ag/HgBa2CaCu2O6+delta interface. It is assumed this insulator is a product created by oxygen non-stoichiometry and decomposition of the superconductor at the interface between both materials. (C) 1999 Elsevier Science B.V. All rights reserved.

  • 39. Kawano, K.
    et al.
    Chakalov, R. A.
    Kong, G.
    Abell, J. S.
    Kahl, S.
    Grishin, Alexander M.
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    BIG films fabricated by PLD for magnetic flux visualisation of YBCO2002Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 372, s. 696-699Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Bi3Fe5O12 (BIG) magneto-optic (MO) films have been grown onto (111) and (100) gadolinium gallium garnet substrates by pulsed laser deposition (PLD). X-ray and transmission electron microscopy measurements have confirmed the epitaxial growth of the BIG films oil both substrate orientations, Faraday rotation angles of both films showed linear field dependence from - 1600 to + 1600 G and the saturated Faraday rotation angle values were similar to5 deg/ pm and similar to7.8 deg/mum for the (111) and (100) oriented films, respectively. A change in the MO contrast of both films in applied magnetic field has been observed and magnetic nux distributions have been visualised in YBa2Cu3O- , (YBCO) bulk superconductor using the (001) oriented BIG film.

  • 40. Khmelevskuyi, S.
    et al.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Mohn, P.
    Frustrated magnetism in superconducting hexagonal Fe: Calculation of inter-atomic pair exchange interactions2007Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 460, s. 647-648Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We calculate magnetic exchange interaction parameters in hcp Fe using magnetic force theorem in density functional theory in a range of volumes, which covers the region of stability of the superconducting state. The calculations are done for a paramagnetic state using disordered local moment model within a local fixed spin-moment constraint. It is found that exchange interaction parameters strongly favor antiferromagnetic inter-plane stacking of the basal hcp planes. At the same time, the nearest neighbor in-plane exchange interaction parameters are also strongly antiferromagnetic, which should lead to magnetic frustrations in the planar triangular lattice. Eventual consequences of the magnetic frustration effects on the interplay between magnetism and superconductivity in hcp Fe under pressure are discussed.

  • 41. Koseoglu, Y
    et al.
    Aktas, B
    Yildiz, F
    Kim, DK
    Toprak, Muhammet S.
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Muhammed, Mamoun
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    ESR studies on high-T-c superconductor MgB22003Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 390, nr 3, s. 197-203Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    MgB2, a high-T-c superconductor, has been studied by electron spin resonance (ESR) techniques at the temperature range of 7-300 K. Polycrystalline powders consisting of MgB2, MgO and MgB4 phases were diluted and oriented in paraffin by applying an external magnetic field of 15 kG. A very narrow (2.5 G), strong, and isotropic signal that corresponded to almost free electron g-values was observed at all temperatures. Both the signal intensity and line width were observed to exhibit strong temperature dependence below T-c. The intensity of the ESR spectra, which corresponds to dc susceptibility, generally obeys the Curie law in this temperature range; However, some critical temperatures (approximately 215, 190, 150, and 39 K) were evident from both intensity and line width curves. While the ESR line is strongly broadened, the signal intensity significantly start to increase just below T = 39 K (corresponding to a transition temperature from normal to superconducting state), passes through a broad maximum around 30 K and then shows a sharp decrease as the temperature is decreased further. The origins of the minor changes both in the intensity and the line width curves at other (higher) critical temperatures are not clear yet. In fact, the change at 215 K was observed to be meta-stable. These minor changes might be taken as signs for changes of local crystalline field symmetry around weakly localized conduction electrons or holes, which are the sources of the ESR signal.

  • 42.
    Langmann, Edwin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Matematisk fysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    On the upper critical field of anisotropic superconductors1991Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 73, s. 347-356Artikkel i tidsskrift (Fagfellevurdert)
  • 43.
    Langmann, Edwin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Matematisk fysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    The critical temperature of superconductors with a cylinder symmetrical Fermi surface1989Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 157, nr 3, s. 415-424Artikkel i tidsskrift (Fagfellevurdert)
  • 44.
    Langmann, Edwin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Matematisk fysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Theory of the upper critical magnetic field without local approximation1989Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 59, s. 561-569Artikkel i tidsskrift (Fagfellevurdert)
  • 45.
    Langmann, Edwin
    et al.
    KTH, Tidigare Institutioner                               , Fysik.
    Lidmar, Jack
    KTH, Tidigare Institutioner                               , Fysik.
    Salmhofer, Manfred
    Wallin, Mats
    KTH, Tidigare Institutioner                               , Fysik.
    Mean field analysis of a model for superconductivity in an anti-ferromagnetic background1998Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 296, s. 119-136Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study a lattice fermion model for superconductivity in the presence of an anti-ferromagnetic background, described as a fixed external staggered magnetic field. We discuss the possibility that our model provides an effective description of coexistence of anti-ferromagnetic correlations and superconductivity. and its possible application to high-temperature superconductivity. We also argue that, under certain conditions, this model describes a variant of the periodic Anderson model for heavy fermions. Using a path integral formulation we construct mean field equations, which we study in some detail. We evaluate the superconducting critical temperature and show thar it is strongly enhanced by anti-ferromagnetic order. We also evaluate the superconducting gap, the superconducting density of states, and the tunneling conductivity, and show that the most stable channel usually has a d(x2-y2)-wave gap.

  • 46.
    Lundqvist, Björn
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Rapp, Östen
    KTH, Tidigare Institutioner, Fysik.
    Andersson, Magnus
    KTH, Tidigare Institutioner, Fysik.
    Field independent vortex solid-to-liquid transition for B parallel to ab in oxygen deficient single crystals of YBa(2)Cu(3)O(7-delta)2000Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 341, nr Part 3, s. 1335-1336Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Single crystals of YBa(2)Cu(3)O(7-delta) provide a suitable test system for vortex dynamics in high temperature superconductors, since the electrical anisotropy gamma = (m(c)/m(ab))(1/2) can easily be varied over a large range by changing the oxygen content. In this paper the vortex solid-to-liquid transition, as determined from a vortex-glass analysis of the resistivity, has been studied for magnetic fields 0<B<less than or equal to>12 T parallel with the ab plane of oxygen deficient single crystals of YBCO. Strikingly for high magnetic fields a field independent vortex solid-to-liquid transition is observed. A possible explanation for this phenomenon involving a crossover to a two-dimensional (2D) system is suggested.

  • 47.
    Lundqvist, Björn
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Rydh, Andreas
    KTH, Tidigare Institutioner, Fysik.
    Rapp, Östen
    KTH, Tidigare Institutioner, Fysik.
    Andersson, Magnus
    KTH, Tidigare Institutioner, Fysik.
    Vortex dynamics in oxygen deficient single crystals of YBa2Cu3O7-delta1997Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 282, s. 1959-1960Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In YBa2Cu3O7-delta (YBCO), oxygen deficiencies in the CuO chains change the coupling between the charge carriers in adjacent superconducting CuO2 planes and thereby the electrical anisotropy, gamma=(m(c)/m(ab))(1/2). Such crystals therefore provide a simple test system for systematic studies of the influence of anisotropy on vortex dynamics. We have studied the vortex glass transition of YBCO single crystals with delta in the range of 0.07 to 0.27, corresponding to gamma between 9 and 18, for magnetic fields 0<B<12 T, along the c-axis. Fits of the glass transition lines to B proportional to (1-T/T-c)(alpha) show large deviations for a combination of high anisotropy and high magnetic fields.

  • 48. Lundqvist, P.
    et al.
    Rapp, Östen.
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Hartmann, O.
    Karlsson, E.
    Wappling, R.
    mu SR study of charge neutrally doped Nd1-2xCaxThxBa2Cu3O7-delta2000Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 338, nr 4, s. 263-268Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Equal amounts of Ca and Th were doped into the Nd1-2xCaxThxBa2Cu3O7-delta superconductor with 0 less than or equal to x less than or equal to 0.10. X-ray diffraction showed a single orthorhombic phase for all samples except at x = 0.10, suggesting a solubility limit below x = 0.10. For increasing doping concentration x the superconducting T-c and the electrical resistivity, rho at 275 K both vary strongly, with a linear decrease of T-c and an increase of rho. The muon spin relaxation rate, sigma, follows the Uemura line for large x, and deviates in the direction of increasing sigma-values for decreasing x. The approach of the data to the Uemura Line was compared between different alloy systems by plotting the normalized distance to the Uemura line as a function of doping concentration. Ca-Th doped samples were found to approach the Uemura line about three times faster than for Ca-Pr doping. The same replacements in Y-123 confirm this result. The strong doping concentration dependence of sigma in Ca-Th substituted samples is explained in terms of electronic disorder effects.

  • 49.
    Magnusson, Niklas
    et al.
    KTH, Tidigare Institutioner, Elkraftteknik.
    Schönborg, Niclas
    KTH, Tidigare Institutioner, Elektrotekniska system.
    Wolfbrandt, Anna
    KTH, Tidigare Institutioner, Elektrotekniska system.
    Hörnfeldt, Sven
    KTH, Tidigare Institutioner, Elektrotekniska system.
    Improved experimental set-up for calorimetric AC loss measurements on HTSs carrying transport currents in applied magnetic fields at variable temperatures2001Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 354, nr 1-4, s. 197-201Artikkel i tidsskrift (Fagfellevurdert)
  • 50.
    Obara, Haruhiko
    et al.
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Andersson, Magnus
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Fivat, Patrice
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Fabrega, Lourdes
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Triscone, Jean-Marc
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Decroux, Michel
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Fischer, Oystein
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Critical current properties of DyBa2Cu3O7/(Y1−xPrx)Ba2Cu3O7 multilayers1994Inngår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 235-240, nr PART 5, s. 2997-2998Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Transport critical currents of DyBa2Cu3O7/(Y1−xPrx)Ba2Cu3O7 (DyBCO/YPrBCO) multilayers have been measured. Using careful meausurements of the temperature and magnetic field dependence of critical current density Jc of the multilayers, we observed two distinct regions in the solid vortex state. From these experimental results, we discuss the dimensionality, the vortex states, and the vortex pinning in the multilayers.

12 1 - 50 of 53
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