Order parameter symmetry in cuprate superconductors

While for the order parameter (i.e. the macroscopic wave function of a superconductor) of hole-doped high-transition-temperature superconductors the d-wave symmetry could be established, for electron-doped cuprates such as the „T’ cuprates“ R_2-xCe_xCuO₄ (R = La, Nd, Pr, Sm, Eu), the situation is still unclear. The same holds for for the superconductor/ferromagnet (S/F) hybrid RuSr₂GdCu₂O₈, and for S/F heterostructures, e.g. based on YBa₂Cu₃O₇ and La_0.67Ca_0.33MnO₃. We investigate the order parameter symmetry with two complementary experimental methods, which are based on either tunneling of Cooper pairs or of quasiparticles. In the first case the super current ininterferometric arrangements of Josephson junctions with suitable geometrie is investigated. In the second case we analyze the quasiparticle conductance of tunnel junctions with respect to the presence of Andreev bound states. both experimental methods are sensitive on very different length scales and ranges of magnetic field and hence give sound evidence on the nature of the superconducting wave function.

Publications concerning this topic

M. Wagenknecht, D. Koelle, R. Kleiner, S. Graser, N. Schopohl, B. Chesca, A. Tsukada, S. T. B. Goennenwein, and R. Gross, Phase diagram of the electron-doped La_2-xCe_xCuO₄ cuprate superconductor from Andreev Bound States at grain boundary junctions", Phys. Rev. Lett. 100, 227001 (2008).

B. Chesca, D. Doenitz, T. Dahm, R. Huebener, D. Koelle, R. Kleiner, Ariando, H. Hilgenkamp, Observation of Andreev bound states in YBa₂Cu₃O_7-x /Au/Nb ramp-type Josephson junctions, Phys. Rev. B 73, 014529, (2006).

T. Nachtrab, Ch. Bernhard, C. T. Lin, D. Koelle, and R. Kleiner, The Ruthenocuprates - Natural Superconductor-Ferromagnet Multilayers, Special Issue on 'Superconductivity and Magnetism', Comptes Rendus Physique Physique 7, 68 (2006).

B. Chesca, M. Seifried, T. Dahm, N. Schopohl, D. Koelle, R. Kleiner, and A. Tsukada, Observation of Andreev Bound States in Bicrystal Grain-Boundary Josephson Junctions Made of the Electron-Doped Superconductor La2−xCexCuO4−y, Phys. Rev. B 71, 104504, (2005).

B. Chesca, K. Ehrhardt, M. Mößle, R. Straub, D. Koelle, R. Kleiner u. A. Tsukada, Phase-sensitive evidence for a predominant d-wave pairing symmetry in the electron doped superconductor La_2-xCe_xCuO_4-y, Physica C 408 321, (2004).

T. Nachtrab, D. Koelle, R. Kleiner, Ch. Bernhard, and C. T. Lin, Intrinsic Josephson Effects in the Magnetic Superconductor RuSr₂GdCu₂O₈, Phys. Rev. Lett. 92, 117001 (2004).

B. Chesca, K. Ehrhardt, M. Mößle, R. Straub, D. Koelle, R. Kleiner, and A. Tsukada, Magnetic-Field Dependence of the Maximum Supercurrent of La_2-xCe_xCuO_4-y Interferometers: Evidence for a Predominant d_x2_-y2 Superconducting Order Parameter, Phys. Rev. Lett. 90, 057004 (2003)

B. Chesca, R. Kleiner, Order parameter phase sensitive experiments and SDJ dc SQUIDs, Physica C 357, 1561 (2001).

B. Chesca, R. Kleiner, Electronic Behavior of SDJ small inductance dc p-SQUIDs, Physica C 350, 180 (2001).

M. Mößle, R. Kleiner, P. Müller, Tunneling between Pb and c-axis oriented Bi₂Sr₂CaCu₂O₈ single crystals, Physica C 317, 392 (1999).

M. Mößle, R. Kleiner, c-Axis Josephson Tunneling between Bi₂Sr₂CaCu₂O_8+x and Pb, Phys. Rev. B 59, 4486 (1999).

R.Kleiner, A.S. Katz, A. G. Sun, R. Summer, D. A. Gajewski, S. H. Han, S. I. Woods, E. Dantsker, B. Chen, K. Char, M. B. Maple, R. C. Dynes and John Clarke, Pair Tunneling from c-axis YBa₂Cu₃O_7-x to Pb: Evidence for s-Wave Component from Microwave Induced Steps, Phys. Rev. Lett. 76, 2161 (1996).

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