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  • 1.
    Andersson, Magnus
    et al.
    KTH, Superseded Departments, Physics.
    Börjesson, Lars
    Physics Department, Chalmers University of Technology.
    Jarlborg, T
    Departement de Physique de la Matière Condensée, Université de Genève.
    Phuong, HV
    Physics Department, Chalmers University of Technology.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    RELATION BETWEEN THE CU(1)-O(4) DISTANCE AND T(C) IN Y1-2XCAXTHXBA2CU3O7-DELTA - RAMAN-SCATTERING AND CALCULATION OF THE ELECTRON-PHONON INTERACTION1992In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 46, no 10, p. 6501-6504Article in journal (Refereed)
    Abstract [en]

    The strong depression of T(c) with Ca-Th substitution in Y1-2xCaxThxBa2Cu3O7-delta has been investigated in a model calculation of the electronic and phononic contributions from the apex oxygen, O(4), on the electron-phonon interaction, lambda. The shift with Ca-Th substitution of the characteristic O(4) vibrational mode was measured by Raman scattering. The electronic part eta of lambda has been calculated at several distances between chain Cu(1) and O(4) in the region of the observed variation with x. Eta was found to depend strongly on this distance. The results show a small increase with x of the O(4) frequency and a strong decrease of eta. Both these factors thus contribute to a decrease of lambda. We therefore find evidence that a decreasing electron-phonon interaction is associated with the depression of T(c) in Ca-Th substituted YBa2Cu3O7-delta.

  • 2.
    Andersson, Magnus
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    de Boissieu, M.
    Bruehne, S.
    Drescher, C.
    Assmus, W.
    Ohahshi, S.
    Tsai, A. P.
    Mihalkovic, M.
    Krajci, M.
    Rapp, Östen
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Electronic and structural properties of Laves-phase MgZn(2) of varying chemical disorder2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 2, p. 024202-Article in journal (Refereed)
    Abstract [en]

    The C14 Laves-phase MgZn(2) has been investigated from 30 to 36 at. % Mg. In this way chemical disorder can be monitored over a limited concentration range and the influence on electron properties can be investigated. Our studies include thermodynamic calculations of atomic configurations of Mg and Zn at off-stoichiometric compositions, electronic-transport measurements, and electronic band-structure calculations of MgZn(2). The disorder introduced by alloying was found to be substitutional for all C14 alloys, and to have a markedly stronger effect on resistivity and magnetoresistance, Delta rho(B)/rho(0), on the Mg-rich side due to strain introduced when Mg substitutes for Zn. rho(T) and Hall constant were characteristic for weakly disordered binary alloys. Delta rho/rho of MgZn(2) was large, reached 6 at 4.2 K and 8 T, and decreased strongly at off-stoichiometric compositions. The results are discussed in view of the band-structure results and in terms of relations between atomic order and electronic properties. Several properties were found to resemble pure Zn. An empirical correlation over more than six orders of magnitude in Delta rho/rho was found for Zn and Zn-based alloys.

  • 3.
    Andersson, Magnus
    et al.
    KTH, Superseded Departments, Physics.
    Eltsev, Yuri
    KTH, Superseded Departments, Physics.
    Lundqvist, Björn
    KTH, Superseded Departments, Physics.
    Rydh, Andreas
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Vortex liquid properties in optimally doped and oxygen-deficient YBa2Cu3O7-delta single crystals2000In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 332, no 1-4, p. 86-92Article in journal (Refereed)
    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].

  • 4.
    Andersson, Magnus
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Feuerbacher, M.
    Rapp, Östen
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Magnetoresistance and Hall effect of the complex metal alloy Mg2Al32008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 2Article in journal (Refereed)
    Abstract [en]

    Unusual electronic transport properties have been found in the rhombohedral beta'-phase of the complex metallic alloy Mg2Al3. The magnetoresistance (MR) is 2 orders of magnitude larger than in the related cubic beta-Mg2Al3-phase and Kohler's rule is strongly violated in the beta'-phase at higher temperatures. Above about 100 K the Hall coefficient R-H of the beta- and beta'-phases are similar and free-electron-like, while in the beta'-phase, R-H changes sign with decreasing temperature at low fields. We have inquired into the sources of these transport anomalies, but have not been able to clearly identify the grounds. Several conventional mechanisms for a large magnetoresistance are discussed, and found not to be applicable. The different properties in the beta- and the beta'-phases are puzzling since the magnitudes of the electrical resistivities are similar and omega(c)tau (cyclotron frequencyxscattering time) is equally small in both phases. The similar temperature range in which anomalies occur in the beta'-phase in the resistivity, the Hall effect, and the magnetoresistance indicates an electronic transition or a change of the electron structure in this phase below about 100 K.

  • 5.
    Andersson, Magnus
    et al.
    KTH, Superseded Departments, Physics.
    Hegedüs, Zsolt
    Arrheniulaboratoriet, Stockholms Universitet.
    Hörlin, Tom
    Arrheniuslaboratoriet, Stockholms Universitet.
    Nygren, Mats
    Arrhemiuslaboratoriet, Stockholms Universitet.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Wen, T. L.
    Arrheniuslaboratoriet, Stockholms Universitet.
    (Ca,Pr) substitutions in Y- and Sm-based 1:2:3 superconductors1992In: / [ed] Per-Anker Lindgård, Odense, Denmark: Risø National Laboratory , 1992, p. 236-236Conference paper (Other academic)
  • 6.
    Andersson, Magnus
    et al.
    KTH, Superseded Departments, Physics.
    Hegedüs, Zsolt
    Arrheniuslaboratoriet, Stockholms Universitet.
    Nygren, Mats
    Arrheniuslaboratoriet, Stockholms Universitet.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    STRUCTURAL, THERMAL AND ELECTRICAL STUDIES OF THE Y1-2XCAXTHXBA2CU3O7-DELTA SYSTEM WITH 0 LESS-THAN-OR-EQUAL-TO 0.201989In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 160, no 1, p. 65-68Article in journal (Refereed)
  • 7.
    Andersson, Magnus
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Lundqvist, Björn
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Rapp, Östen
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Vortex liquid-to-solid transition in underdoped YBa2Cu3O7-delta single crystals with B parallel to ab2003In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 388, p. 691-692Article in journal (Refereed)
    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.

  • 8.
    Andersson, Magnus
    et al.
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    MAGNETORESISTANCE MEASUREMENTS ON (CA,TH)-DOPED YBA2CU3O7-DELTA1991In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 185, p. 1901-1902Article in journal (Refereed)
    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.

  • 9.
    Andersson, Magnus
    et al.
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    MAGNETORESISTANCE MEASUREMENTS ON POLYCRYSTALLINE YBA2CU3O7-DELTA1991In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 44, no 14, p. 7722-7725Article in journal (Refereed)
    Abstract [en]

    The magnetoresistance of a polycrystalline sample of YBa2Cu3O7-delta has been measured by an ordinary resistive method at temperatures from about 1 to 15 K above T(c) and in magnetic fields up to 12 T. From our experimental results and the theory of Hikami and Larkin, we obtain values of the coherence lengths xi-ab = 15.6 angstrom and xi-c = 3.6 angstrom and of the phase-breaking time tau-phi = 1.8 x 10(-13) s.

  • 10.
    Andersson, Magnus
    et al.
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    MAGNETORESISTANCE MEASUREMENTS ON SINTERED YBA2CU3O7-DELTA1990In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 165, p. 1365-1366Article in journal (Refereed)
  • 11.
    Andersson, Magnus
    et al.
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    UPPER CRITICAL MAGNETIC-FIELD OF Y1-2XCAXTHXBA2CU3O7-DELTA1989In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 162, p. 725-726Article in journal (Refereed)
  • 12.
    Andersson, Magnus
    et al.
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Hegedüs, Zsolt
    Arrheniuslaboratoriet, Stockholms Universitet.
    Wen, TL
    Arrheniuslaboratoriet, Stockholms Universitet.
    Nygren, Mats
    Arrheniuslaboratoriet, Stockholms Universitet.
    STRUCTURAL AND SUPERCONDUCTING PROPERTIES OF Y1-2XCAXPRXBA2CU3O7-GAMMA1992In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 190, no 3, p. 255-260Article in journal (Refereed)
    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.

  • 13.
    Andersson, Magnus
    et al.
    KTH, Superseded Departments (pre-2005), Physics.
    Rapp, Östen
    KTH, Superseded Departments (pre-2005), Physics.
    Tellgren, Roland
    Institutet för kemi, Uppsala Universitet.
    Neutron-diffraction studies of Ca-Pr doped YBa2Cu307-delta1993In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 205, no 1-2, p. 105-110Article in journal (Refereed)
    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.

  • 14.
    Andersson, Magnus
    et al.
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Tellgren, Roland
    Institutet för kemi, Uppsala Universitet.
    NEUTRON-DIFFRACTION STUDIES OF Y1-2XCAXTHXBA2CU3O7-DELTA WITH X-LESS-THAN=0.11991In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 185, p. 915-916Article in journal (Refereed)
    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.

  • 15.
    Andersson, Magnus
    et al.
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Wen, TL
    Arrheniuslaboratoriet, Stockholms Universitet.
    Hegedüs, Zsolt
    Arrheniuslaboratoriet, Stockholms Universitet.
    Nygren, Mats
    Arrheniuslaboratoriet, Stockholms Universitet.
    CA AND PR SUBSTITUTION IN Y-BASED AND SM-BASED 1-2-3 COMPOUNDS1993In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 48, no 10, p. 7590-7597Article in journal (Refereed)
    Abstract [en]

    Substitution with equal amounts of Ca and Pr has been studied mainly in Y- and Sm-based 1:2:3 samples and with some results also for Nd-based samples. Structural and chemical analysis and measurements of the superconducting T(c) and the upper critical magnetic field were performed. It was found that Ca and Pr can be dissolved in the orthorhombic structure up to about 25 at. % each in both Y- and Sm-based samples while for larger concentrations, only Pr continued to enter into the 1:2:3 structure. The depression of T(c) with Ca-Pr doping was found to be linear in concentration in contrast to the accelerated decrease in samples doped with only Pr. The rate of depression of T(c) increased in the sequence Y-, Sm-, and Nd-based hosts. The results suggest that Ca-Pr doping isolates a characteristic Pr-impurity effect in 1:2:3 samples. The critical magnetic-field slopes of Y- and Sm-based samples were almost independent of Ca-Pr content in the cosolubility region while a strong decrease was observed for larger Pr content, similar to 1:2:3 samples doped with Pr only. These results suggest an almost-temperature-independent magnetic pair-breaking effect by Pr.

  • 16.
    Andersson, Magnus
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Rydh, Andreas
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Rapp, Östen
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Scaling of the vortex-liquid resistivity in optimally doped and oxygen-deficient YBa2Cu3O7-delta single crystals2001In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 63, no 18, p. 1845111-1845119Article in journal (Refereed)
    Abstract [en]

    The consequences of a recently proposed model [A. Rydh. O. Rapp. and M. Andersson. Phys. Rev. Lett. 83. 1850 (1999)] for the vortex-liquid resistivity close to a vortex liquid-to-glass transition are anal-zed in detail. We find a detailed quantitative agreement between the model and resistivity measurements on disordered, optimally doped YBa2Cu3O7-delta single crystals. For temperatures below the superconducting transition temperature. a scaling of all measured resistivity curves in magnetic field (0<B12 T) is obtained. Possible ways of slightly modifying the model in order to fully describe resistivity measurements on more anisotropic underdoped oxygen-deficient YBa2Cu3O7-delta single crystals are suggested. The physical interpretation of the model and its connection to other models of the vortex-liquid resistivity are discussed. in particular, we find close connections to vortex glass models and to a generalized Coulomb gas model.

  • 17.
    Andersson, Magnus
    et al.
    KTH, Superseded Departments, Physics.
    Rydh, Andreas
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Vortex liquid resistivity in disordered YBa2Cu3O7-delta single crystals2000In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 341, p. 1239-1240Article in journal (Refereed)
    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.

  • 18.
    Anderssson, Magnus
    et al.
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Tellgren, Roland
    Institutet för kemi, Uppsala Universitet.
    NEUTRON-DIFFRACTION STUDIES OF INTERATOMIC DISTANCES IN THE Y1-2XCAXTHXBA2CU3O7-DELTA SYSTEM1992In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 81, no 5, p. 425-429Article in journal (Refereed)
    Abstract [en]

    Neutron diffraction studies have been performed for three samples of Y(1-2x)Ca(x)Th(x)Ba2Cu3O7-delta with 0 less-than-or-equal-to x less-than-or-equal-to 0.1. With increasing x, a decreased puckering of the Cu-O planes is found. Changes in copper oxygen distances are generally small. Evidence is found for a small increase in the distance between Cu(1) and O(4) (on the cell edge) with increased CaTh concentration. An increased oxygen disorder is observed at x = 0.1.

  • 19. Axnas, J.
    et al.
    Bryntse, I.
    Safonova, I.
    Rapp, Östen.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Magnetoconductivity of polycrystalline Hg,Tl-12232000In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 284, p. 1009-1010Article in journal (Refereed)
    Abstract [en]

    The magnetoconductivity of polycrystalline Hg1-xTlxBa2Ca2Cu3O8+delta With x = 0 and 0.2 has been measured above T-c and analysed in terms of superconducting fluctuations. Such studies are numerous and successful for Y- and Bi-based materials, but still rare for Hg- and Tl-based materials. Results for the coherence lengths and the role of the Maki-Thompson contribution are briefly discussed.

  • 20. Bjornangen, T.
    et al.
    Axnas, J.
    Eltsev, Y.
    Rapp, Östen.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    In-plane anisotropy and chain contribution from the magnetoresistivity of YBa2Cu3O7-delta2000In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 341, p. 1885-1886Article in journal (Refereed)
    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.

  • 21. Bjornangen, T.
    et al.
    Axnas, J.
    Eltsev, Y.
    Rydh, A.
    Rapp, Östen.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    In-plane anisotropy and possible chain contribution to magnetoconductivity in YBa2Cu3O7-delta2001In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 6322, no 22Article in journal (Refereed)
    Abstract [en]

    The magnetoresistivity of untwinned YBa2Cu3O7-delta Single crystals was measured in magnetic fields up to 12 T-c for B parallel toc and B parallel to ab. at temperatures up to T-c + 84 K and T-c + 50 K, respectively. Two issues were addressed; determination of the in-plane coherence length anisotropy gamma=xi (b)/xi (a) and discussion of the role of the CuO chains in the magnetoconductivity Delta sigma. A fluctuation conductivity theory that allows for an in-plane coherence length anisotropy (xi (a)not equal xi (b)) as well as an extension of the usual Aronov-Hikami-Larkin theory that does not, were used in analyses. The results suggest that the anisotropy gamma is close to 1. The analyses also suggest a contribution to the magnetoconductivity from the CuO chains of a sign which depends on the direction between held and current.

  • 22. Bjornangen, T.
    et al.
    Rydh, A.
    Rapp, Östen.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Multiterminal transport measurements: In-plane anisotropy and vortex liquid correlation in YBa2Cu3O7-delta2001In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 64, no 22Article in journal (Refereed)
    Abstract [en]

    Using a modified pseudoflux transformer geometry, the in-plane anisotropy and vortex-liquid correlation of an untwinned YBa2Cu3O7-delta single crystal have been studied. The square-shaped, multiterminal sample design allows comparative studies of a- and b-axis properties for arbitrarily oriented magnetic fields. We compare the in-plane resistivity in the case of intrinsic pinning with the longitudinal resistivity, i.e., with the resistivity in absence of a macroscopic Lorentz force. The relative ratio between resistivities rho (a) and rho (b) in the vortex state can be made to vary over a wide range by controlling the direction of the applied magnetic field. Evidence is found for almost isotropic fluctuations corresponding to a fluctuation anisotropy gamma (A)(ab)approximate to1.1, noted to be clearly lower than the anisotropy gamma (ab)=1.27 obtained from the vortex phase diagram.

  • 23. Bjornangen, T.
    et al.
    Rydh, A.
    Rapp, Östen.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Vortex liquid and solid correlation in untwinned YBa2Cu3O7-delta2003In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 388, p. 727-728Article in journal (Refereed)
    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.

  • 24.
    Björnängen, Therese
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Fors, Rickard
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Eltsev, Yurii
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Rapp, Östen
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Vortex correlation parallel in underdoped and perpendicular to H vertical bar vertical bar ab YBa2Cu3O7-delta2004In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 408-10, p. 564-565Article in journal (Refereed)
    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.

  • 25.
    Börjesson, Lars
    et al.
    Dept. Physics, Chalmers University of Technology.
    Phuong, H.V.
    Dept. Physics, Chalmers University of Technology.
    Jarlborg, Tomas
    Dept. de la Matière Condensée, University of Geneva.
    Andersson, Magnus
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Ca-Th substitution in YBa2Cu3O7-delta: Raman scattering and calculation of the electron-phonon interaction1992In: Proceedings of the Joint Nordic Spring Meeting '92 / [ed] Per-Anker Lindgård, Roskilde, Denmark: Risø National Laboratory , 1992, p. 235-235Conference paper (Other academic)
  • 26.
    Espinosa-Arronte, Beatriz
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Rapp, Östen
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Andersson, Magnus
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Scaling of the vortex liquid c-axis resistivity in underdoped YBa2Cu3O7-[delta]2004In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 408, p. 583-584Article in journal (Refereed)
    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.

  • 27. Ghorbani, S. R.
    et al.
    Rapp, Östen.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    An anomalous dip in thermoelectric power of Nd1-xPrxBa2Cu3O7-delta2003In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 388, p. 351-352Article in journal (Refereed)
    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.

  • 28.
    Ghorbani, Shaban Reza
    et al.
    KTH, Superseded Departments, Physics.
    Andersson, Magnus
    KTH, Superseded Departments, Physics.
    Lundqvist, Pieter
    KTH, Superseded Departments, Physics.
    Valldor, M.
    Arrheniuslaboratoriet, Stockholms Universitet.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Thermoelectric power and resistivity of Nd1-xCaxBa2Cu3Oy and Nd1-xLaxBa2Cu3Oy2000In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 339, no 4, p. 245-252Article in journal (Refereed)
    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.

  • 29.
    Ghorbani, Shaban Reza
    et al.
    Department of Physics, Tarbiat Muallem University of Sabzevar, Iran.
    Andersson, Magnus
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Rapp, Östen
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Disorder Driven Localization in Charge Neutrally Doped 123 Superconductors2006In: Low Temperature Physics / [ed] Takano, Y; Hershfield, SP; Hirschfeld, PJ; Goldman, AM, 2006, Vol. 850, p. 439-440Conference paper (Refereed)
    Abstract [en]

    Charge neutral dopings with equal amounts of CaTh or CaPr on rare earth site in Nd-123 have been investigated by studies of the normal state electrical resistivity, p, the Seebeck coefficient S, and the Hall coefficient R-H. In spite of comparable rates of depression of the superconducting T, significant differences are observed in the doping concentration dependence of p, S, and RH between the two dopings. These results are discussed in terms of disorder induced localization.

  • 30.
    Ghorbani, Shaban Reza
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Andersson, Magnus
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Rapp, Östen
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Neutron diffraction studies of Nd1-xPrxBa2Cu3O7-delta: Evidence for hole localization2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69, no 1, p. 145031-Article in journal (Refereed)
    Abstract [en]

    Sintered samples of Nd1-xPrxBa2Cu3O7-delta with x=0, 0.05, 0.10, 0.15, 0.20, and 0.30 have been studied by neutron diffraction, x-ray diffraction, and resistivity measurements. Sample stoichiometry was carefully checked. Atomic distances within the unit cell and the oxygen content were shown to be almost independent of Pr doping. Bond valence sums (BVSs) were calculated from the neutron diffraction data assuming either a constant valence or a mixed valence for Cu and Pr ions. The planar Cu2 valence is independent of Pr doping and the chain Cu1 valence is roughly constant, while the hole concentration in the planes and chains decrease with increasing Pr doping for both BVS calculation methods. All together, this indicates that hole localization on the Nd(Pr) site is a main reason for the decrease of the hole concentration in the planes. A consistent relation between the hole concentration in the planes calculated from the constant valence method and the depression of the critical temperature is also obtained, both for Pr-doped Nd-123 and for Y(Pr)-123 studied previously.

  • 31.
    Ghorbani, Shaban Reza
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Andersson, Magnus
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Rapp, Östen
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Normal state Hall effect in Nd1-xCaxBa2Cu3O7-delta: competition between added charge and disorder2003In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 390, no 2, p. 160-166Article in journal (Refereed)
    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, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Lundqvist, Pieter
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Andersson, Magnus
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Valldor, M.
    Rapp, Östen
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Thermoelectric power and resistivity of Nd1-xPrxBa2Cu3O7-delta2001In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 353, no 1-2, p. 77-84Article in journal (Refereed)
    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, Superseded Departments, Physics.
    Eltsev, Yuri
    KTH, Superseded Departments, Physics.
    Andersson, Magnus
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    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 density1999In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 322, no 3-4, p. 203-208Article in journal (Refereed)
    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.
    Eltsev, Y.
    Rapp, Östen.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Three-dimensional XY critical fluctuations of the dc electrical conductivity in Bi2Sr2CaCu2O8+delta single crystals2000In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 61, no 17, p. 11776-11779Article in journal (Refereed)
    Abstract [en]

    A method is presented to analyze the dc critical fluctuation conductivity Delta sigma of Bi2Sr2CaCu2O8+delta single crystals in zero magnetic field. Two crossovers are obtained upon approaching T-c; first the Ginzburg crossover from the mean-held region to the initial critical regime, where the critical exponent a of Delta sigma changes from -1/2 to -2/3, and then, closer to T-c, a crossover of alpha form -2/3 to 1/3 in the critical region. Good agreement is found with the expectations from the three-dimensional XY model.

  • 35. Han, S. H.
    et al.
    Lundqvist, B.
    Eltsev, Y.
    Rapp, Östen.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Studies of dynamic critical behaviour in YBa2Cu3O7-delta single crystals2000In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 341, p. 1855-1856Article in journal (Refereed)
    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.

  • 36.
    Han, Shunhui
    et al.
    KTH, Superseded Departments, Physics. KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Axnäs, Johan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Zhao, B R
    Rapp, Östen
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Fluctuation conductivity at high temperatures in polycrystalline Hg, Tl-1223 - Is there ID fluctuation behavior?2004In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 408, p. 679-680Article in journal (Refereed)
    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.

  • 37.
    Han, Shunhui
    et al.
    KTH, Superseded Departments, Physics.
    Hegedüs, Zsolt
    Arrheniuslaboratoriet, Stockholms Universitet.
    Andersson, Magnus
    KTH, Superseded Departments, Physics.
    Nygren, Mats
    Arrheniuslaboratoriet, Stockholms Universitet.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    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 phase1990In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 169, no 3-4, p. 250-256Article in journal (Refereed)
  • 38. Haussermann, U.
    et al.
    Bostrom, M.
    Viklund, P.
    Rapp, Östen.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Bjornangen, T.
    FeGa3 and RuGa3: Semiconducting intermetallic compounds2002In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 165, no 1, p. 94-99Article in journal (Refereed)
    Abstract [en]

    The intermetallic compounds FeGa3 and RuGa3 were prepared from the elements using a Ga flux and their structures were refined from single-crystal X-ray data. Both compounds crystallize with the FeGa3 structure type (tetragonal, space group P4(2)/mnm, Z=4). Electrical resistivity measurements revealed a semiconducting behavior for FeGa3 and RuGa3, which is in contrast to the good metallic conductivity observed for the isotypic compound CoGa3. The origin of the different electronic properties of these materials was investigated by first-principle calculations. It was found that in compounds adopting the FeGa3 structure type the transition metal atoms and Ga atoms interact strongly. This opens a d-p hybridization bandgap with a size of about 0.31 eV in the density of states at the Fermi level for 17-electron compounds (i.e., FeGa3 and RuGa3). The electronic structure of CoGa3 (an 18-electron compound) displays rigid band behavior with respect to FeGa3. As a consequence, the Fermi level in CoGa3 becomes located above the d-p hybridization gap which explains its metaltic conductivity.

  • 39.
    Hegedüs, Zsolt
    et al.
    Arrheniuslaboratoriet, Stockholms Universitet.
    Nygren, Mats
    Arrheniuslaboratoriet, Stockholms Universitet.
    Andersson, Magnus
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    On the preparation of the high temperature superconductor YBa2Cu4O81991In: ICMAS-91: International conference on modern aspects of superconductivity, Paris, 7-8 octobre 1991 / [ed] B. Raveau, K. Wasa and R. Suryanayanan, Gournay-sur-Marne: Institute for Industrial Technolog Transfer (IITT) , 1991, p. 107-111Conference paper (Refereed)
  • 40.
    Holm, William
    et al.
    KTH, Superseded Departments, Physics.
    Andersson, Magnus
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Helmersson, Ulf
    Fysik, Linköpings Universitet.
    Han, Z.
    Fysik, Linköpings Universitet.
    Study of magnetoresistance in oriented yba2cu3O7-delta thin-film1994In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 194, p. 2291-2292Article in journal (Refereed)
    Abstract [en]

    The magnetoresistance of a c-axis oriented YBa2Cu3O7-delta thin film has been measured in magnetic fields, B, up to 12 T. The magnetic field was oriented both perpendicularly and parallel to the basal plane. The temperatures ranged up to epsilon = (T-T(c))/T(c) almost-equal-to 1/3 for B parallel-to c, while for B perpendicular-to the range was limited to epsilon less-than-or-equal-to 0.16. Analysis of the data in terms of superconducting fluctuations described by the Aronov-Hikami-Larkin theory is discussed.

  • 41.
    Holm, William
    et al.
    KTH, Superseded Departments, Physics.
    Andersson, Magnus
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Ivanov, Z. G.
    Dept. Physics, Chalmers University of Technology.
    Claeson, Tord
    Dept. Physics, Chalmers University of Technology.
    Negative magnetoresistance in YBa2Cu3O7-delta thin films1992In: Proceedings of the Joint Nordic Spring Meeting '92 / [ed] Per-Anker Lindgård, Odense, Denmark: Risø National Laboratory , 1992, p. 241-241Conference paper (Other academic)
  • 42.
    Holm, William
    et al.
    KTH, Superseded Departments, Physics.
    Andersson, Magnus
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Ivanov, Z.G.
    Department of Physics, Chalmers University of Technology.
    Engström, U.
    Department of Physics, Chalmers University of Technology.
    Negative magnetoresistance in an yba2cu3O7-delta thin-film1994In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 194, p. 2309-2310Article in journal (Refereed)
    Abstract [en]

    Negative magnetoresistance was observed in a thin YBa2Cu3O7-delta film which could be correlated with the presence of magnetic impurities. After empirical compensation for this effect the fluctuation conductivity was well described by the Aronov-Hikami-Larkin theory.

  • 43.
    Holm, William
    et al.
    KTH, Superseded Departments, Physics.
    Andersson, Magnus
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Kulikov, M.A.
    Academy of Sciences of Russia, Moscow.
    Makarenko, I.N.
    Academy of Sciences of Russia, Moscow.
    Anisotropic fluctuation magnetoconductivity in a yba2cu3O7-delta single-crystal above tc1993In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 48, no 6, p. 4227-4230Article in journal (Refereed)
    Abstract [en]

    The in- and out-of-plane magnetoresistance of a single crystal of YBa2Cu3O7-delta has been measured at temperatures above T(c) in magnetic fields up to 12 T. A Montgomery-type contact configuration was used with corrections for the finite size of the contacts taken into account. For temperatures up to 2.5 K above T(c) the data are well described by both the Aronov-Hikami-Larkin theory for a layered superconductor (applicable only for the in-plane magnetoconductivity) and the Ginzburg-Landau theory for a three-dimensional anisotropic superconductor (applicable for both the in-plane and the out-of-plane magnetoconductivity). All three analyses give consistent results for the coherence lengths.

  • 44. Karkin, A. E.
    et al.
    Goshchitskii, B. N.
    Voronin, V. I.
    Poon, S. J.
    Srinivas, V.
    Rapp, Östen.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Monitoring an insulator-metal transition in icosahedral AlPdRe by neutron irradiation2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, no 9Article in journal (Refereed)
    Abstract [en]

    The intrinsic disorder effect on the electrical resistivity and magnetoresistance (MR) of icosahedral AlPdRe is studied by use of high-energy neutron irradiation. The icosahedral phase is preserved under irradiation with a decrease of x-ray peak intensity and volume of the coherent icosahedral phase. An insulator-metal transition, as observed in the MR, can be driven by the irradiation and is monitored by the resistance ratio R[=rho(4.2 K)/rho(295 K)]. The relation of MR vs R was found to be similar for samples of a widely different history.

  • 45.
    Lundqvist, Björn
    et al.
    KTH, Superseded Departments, Physics.
    Eltsev, Yuri
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Andersson, Magnus
    KTH, Superseded Departments, Physics.
    Vortex dynamics in different magnetic field directions of untwinned YBa2Cu3O7-delta single crystals1996In: Czechoslovak Journal of Physics, ISSN 0011-4626, E-ISSN 1572-9486, Vol. 46, no Suppl. 3, p. 1705-1706Article in journal (Refereed)
    Abstract [en]

    Current-Voltage (I-V) characteristics have been measured on an untwinned single crystal of YBa2Cu3O7-delta with the current along the b-axis and with the applied magnetic field along various crystallographic axes. Measurements with the magnetic field in the ab-plane resulted in a different qualitative behaviour of the I-V characteristics than for the field applied along the c-axis.

  • 46.
    Lundqvist, Björn
    et al.
    KTH, Superseded Departments, Physics.
    Larsson, J.
    KTH, Superseded Departments, Physics.
    Herting, Anna
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Andersson, Magnus
    KTH, Superseded Departments, Physics.
    Ivanov, Z. G.
    Dept. Physics, Chalmers University of Technology.
    Johansson, L. G.
    Göteborgs Universitet.
    Cutoff of the vortex-glass behavior in Tl(2)Ba(2)CaCu(2)O(8+delta) superconducting thin films1998In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 58, no 10, p. 6580-6584Article in journal (Refereed)
    Abstract [en]

    The vortex dynamics of a Tl(2)Ba(2)CaCu(2)O(8+delta) thin film has been measured by electrical resistivity and I-V characteristics. The temperature T*(B) defined from a vortex-glass analysis of the resistivity in the vortex liquid state using the Vogel-Fulcher relation is shown to be consistent with a vortex-glass-like scaling of the I-V characteristics in the high dissipation regime. Below T*, there is however a significant temperature range in which the flux creep does not vanish at low currents. This suggests that the transition into a glassy vortex state is cut off at some length scale.

  • 47.
    Lundqvist, Björn
    et al.
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Andersson, Magnus
    KTH, Superseded Departments, Physics.
    Experimental evidence for a three-dimensional-two-dimensional crossover for magnetic fields parallel to the ab plane in oxygen-deficient single crystals of YBa2Cu3O7-delta2000In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 62, no 5, p. 3542-3546Article in journal (Refereed)
    Abstract [en]

    Resistive measurements on oxygen-deficient YBa2Cu3O7-delta single crystals of varying anisotropy gamma (22 less than or equal to gamma less than or equal to 36) have been used for investigations of the transition into a glassy vortex state for magnetic fields 0 less than or equal to B less than or equal to 12 T parallel to the ab plane. When B is accurately aligned parallel to the nb plane there is a remarkable change in behavior to a field-independent vortex solid-to-liquid transition at high magnetic fields. A possible explanation is suggested for the vertical transition involving a complete decoupling of the superconducting planes that leads to a two-dimensional system where the resistivity is given by nucleation of vortex-antivortex pairs.

  • 48.
    Lundqvist, Björn
    et al.
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Andersson, Magnus
    KTH, Superseded Departments, Physics.
    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)2000In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 341, no Part 3, p. 1335-1336Article in journal (Refereed)
    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.

  • 49.
    Lundqvist, Björn
    et al.
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Andersson, Magnus
    KTH, Superseded Departments, Physics.
    Vortex dynamics for in- and out-of-plane magnetic fields in oxygen deficient single crystals of YBa2Cu3O7-delta2000In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 284, no Part. 1, p. 705-706Article in journal (Refereed)
    Abstract [en]

    The resistive transition into a glassy vortex state in oxygen deficient single crystals of YBa2Cu3O7-delta (YBCO) has been studied for magnetic fields 0 less than or equal to B less than or equal to 12 T along the crystallographic c-axis, parallel to the ab plane, and also with a small misalignment of 1 degrees from the ab plane. Angular sweeps of the magnetic field reveal a sharp dip in the resistivity for B \textbackslash\textbackslash ab, which is attributed to intrinsic pinning of vortices between the planes. For Bile the vortex glass line is well described by B-g(T)= B-0[(1 - T/T-c)/(T/T-c)](alpha), where B-0 is anisotropy dependent and alpha approximate to 1.0-1.2. For B \textbackslash\textbackslash ab the behaviour is significantly different, and at high magnetic fields a change to a field-independent vortex solid-to-liquid transition is observed. This behaviour disappears for small misalignments between B and ab.

  • 50.
    Lundqvist, Björn
    et al.
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Andersson, Magnus
    KTH, Superseded Departments, Physics.
    Eltsev, Y.
    ISTEC, Tokyo.
    Nearly field-independent in-plane vortex solid-to-liquid transition in the c-axis resistivity of oxygen deficient single crystals of YBa2Cu3O7-delta2001In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 64, no 6, p. 060503-Article in journal (Refereed)
    Abstract [en]

    The c-axis resistivity has been measured in oxygen deficient single crystals of YBa2Cu3O7-delta (anisotropy gamma approximate to 24-29) with the magnetic field B accurately aligned parallel to the ab plane. An almost field-independent vortex solid-to-liquid transition is observed at high fields in contrast to the usual field-dependent one, which is recovered for a small misalignment between B and ab. This observation challenges previous interpretations of the same effect in the ab resistivity as coming from a smectic vortex state or a decoupling of the superconducting planes.

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