Theory of Local Density of States ofd_x²-y²-Wave Superconducting State Near the Surfaces of thet-JModel

Abstract

Spatial dependencies of the pair potential and the local density of states near the surfaces of d x 2 −y 2 -wave superconductors are studied theoretically. The calculation is based on the t-J model within a mean-field theory with Gutzwiller approximation. Various types of surface geometries are considered. Similar to our result in the extended Hubbard model, it is found that the formation of zero-energy states strongly depends on the surface geometry. In addition to this feature, the zero-energy states give peak splitting for the (110) surfaces when the superexchange interaction J is large. This is due to the induced s-wave component near the surface.The present result explains the microscopic origin of the spontaneous time-reversal symmetry breaking at the surfaces of high-T c superconductors.KEYWORDS: t-J model, d-wave superconductor, Gutzwiller approximation, scanning tunneling spectroscopy, zero-energy peaks, spontaneous time-reversal symmetry breakingThe t-J model 1) is believed to explain the phase diagram of high-T c materials including the socalled pseudogap above T c and thus is a realistic model for high-T c superconductors. 2) Although there are many works regarding this model, the quasiparticle properties in nonuniform systems including surfaces or interfaces are not clear at this stage except for those in the case with a vortex. 3) Since d x 2 −y 2 -wave pair potential is the most promising symmetry in the t-J model for actual doping concentrations, we expect an interference effect of the quasiparticle due to the signchange of the pair potential 4) at the surface.Recent theoretical works within quasiclassical approximation revealed a novel interference effect peculiar to the unconventional superconductivity. 5,6,7,8,9,10,11) One of the interesting interference effects is the appearance of zero-energy states (ZES) at the surface, which is due to the sign-change of pair potential when the quasiparticles are reflected at the surface. 7) This localized ZES manifests itself as a zero-bias conductance peak (ZBCP) in tunneling experiments. 5, 12) A recent experiment 1

Andreev bound states in high temperature superconductors

“…That is, the measurement of the conductance in ab-plane tunneling experiments can give information on the presence of a surface order parameter in HTS that spontaneously breaks time reversal symmetry. Recently, this effect has been found to be consistent with the t − J-model [61] in the case of sufficiently large J at the surface of a d-wave superconductor [62,63].…”

Gutzwiller–RVB theory of high-temperature superconductivity: Results from renormalized mean-field theory and variational Monte Carlo calculations

“…The renormalized mean field Hamiltonian can then be written as [83], . The self-consistent determination of order parameters within the renormalized Bogoliubov-de Gennes theory was also applied to study surface effects in 2D superconducting states [144,145].…”

Zero-bias conductance peak splitting due to multiband effect in tunneling spectroscopy of organic superconductors

“…As regards the roughness of the surface, we believe it is necessary to study tunneling spectroscopy of κ-(BEDT-TTF) 2 Cu(NCS) 2 in the presence of atomic scale roughness as done by Tanuma et al on a lattice model. 21,22 As for the issue of random scattering effect by impurities, Asano et al 37 have shown, both from analytical and numerical calculation beyond quasiclassical approximations, that impurity scattering near the interface in the high-T C cuprates can induce a splitting or a disappearance of the ZBCP. From this viewpoint, it would also be interesting to study the impurity scattering effect in κ-(BEDT-TTF) 2 Cu(NCS) 2 .…”