Jian-Xin Zhu

Proximity effect, quasiparticle transport, and local magnetic moment in ferromagnet-d-wave-superconductor junctions

The proximity effect, quasiparticle transport, and local magnetic moment in ferromagnet‐ d-wave-superconductor junctions with

Quasiparticle States around a Nonmagnetic Impurity in a d-Density-Wave State of High-Tc Cuprates

110%-oriented interface are studied by solving self-consistently the Bogoliubov‐de Gennes equations within an extended Hubbard model. It is found that the proximity induced order parameter oscillates in the ferromagnetic region. The modulation period is shortened with the increased exchange field while the oscillation amplitude is depressed by the interfacial scattering. With the determined superconducting energy gap, a transfer matrix method is proposed to compute the subgap conductance within a scattering approach. Many interesting features including the zero-bias conductance dip and splitting are exhibited with appropriate values of the exchange field and interfacial scattering strength. The conductance spectrum can be influenced seriously by the spin-flip interfacial scattering. In addition, a sizable local magnetic moment near the

Effect of unitary impurities on non-STM types of tunneling in high-T-c superconductors

110%-oriented surface of the d-wave superconductor is discussed.

Local Quasiparticle States near a Unitary Impurity with Induced Magnetic Moment in a d-Wave Superconductor

The electronic structure around a single nonmagnetic impurity in the d-density-wave (DDW) ordering is studied. It is found that a single subgap resonance peak appears in the local density of states around the impurity. In the unitary limit, the position of this resonance peak shifts away from the Fermi energy in accord with the chemical potential. This result is dramatically different from the case of the pure superconducting state for which the impurity resonant energy is approximately pinned at the Fermi level. This can be used to probe the existence of the DDW ordering in cuprates.

c-axis response of a high-Tc superconductor with d-density-wave order

Based on an extended Hubbard model, we present calculations of both the local (i.e., single-site) and spatially averaged differential tunneling conductance in d-wave superconductors containing nonmagnetic impurities in the unitary limit. Our results show that a random distribution of unitary impurities of any concentration can at most give rise to a finite zero-bias conductance (with no peak there) in spatially averaged non-STM type of tunneling. This is in spite of the fact that local tunneling in the immediate vicinity of an isolated impurity does show a conductance peak at zero bias. We also find that to give rise to even a small zero-bias conductance peak in the spatially averaged type of tunneling the impurities must form dimers, trimers, etc., along the [110] directions. In addition, we find that the most recently observed novel pattern of the tunneling conductance around a single impurity by Pan et al. [Nature (London) 403, 746 (2000)] can be explained in terms of a realistic model of the tunneling configuration which gives rise to the experimental results reported there. The key feature in this model is the blocking effect of the BiO and SrO layers which exist between the tunneling tip and the

SPONTANEOUS FLUX IN A D-WAVE SUPERCONDUCTOR WITH TIME-REVERSAL-SYMMETRY-BROKEN PAIRING STATE AT 110-ORIENTED BOUNDARIES

{\mathrm{CuO}}_{2}

Local quasiparticle states around an Anderson impurity in a d -wave superconductor: Kondo effects

layer being probed.

Competing effects of mass anisotropy and spin-Zeeman coupling on the upper critical field of a mixedd- ands-wave superconductor

The local quasiparticle density of states around a unitary impurity with a Kondo-like magnetic moment induced at its nearest neighbors in a d-wave superconductor is studied within the slaveboson mean-field approach. The Hamiltonian is exactly diagonalized and the results are obtained self-consistently. We show that the interference between the strong impurity potential scattering and the Kondo effect leads to novel quasiparticle spectra around the impurity, which are strikingly different from the case of a single unitary or magnetic impurity. The recent STM image of the local differential tunneling conductance around a Zn impurity in a high-Tc cuprate can be essentially explained if the blocking effect of BiO surface layer between the tip and probed CuO2 plane [Zhu et al., Phys. Rev. B 62, 6207 (2000)] is taken into account.

SPIN-POLARIZED QUASIPARTICLE TRANSPORT IN FERROMAGNET-D-WAVE-SUPERCONDUCTOR JUNCTIONS WITH A 110 INTERFACE

The microscopic origin of the pseudogap state that exists in the underdoped cuprates remains unknown. The c-axis properties in the pseudogap regime are particularly anomalous. We use a recently proposed model of a d density wave that leads to staggered currents and the doubling of the unit cell to investigate the c-axis kinetic energy and the optical sum rule. The density of states expected in the model is also considered.

Lattice model for the broken-time-reversal-symmetry pairing state near a surface of d -wave superconductors

The induction of an s-wave component in a d-wave superconductor is considered. Near the {110}-oriented edges of such a sample, the induced s-wave order parameter together with d-wave component forms a complex combination d+e^{i\phi} s, which breaks the time reversal symmetry (BTRS) of the pairing state. As a result, the spontaneous current is created. We numerically study the current distribution and the formation of the spontaneous flux induced by the current. We show that the spontaneous flux formed from a number of defect lines with {110} orientation has a measurable strength. This result may provide a unambiguous way to check the existence of BTRS pairing state at {110}-oriented boundaries.