C.-D. Gong

Exact solution of anisotropic antiferromagnetic alternating Heisenberg–Ising spin chain

Abstract We extend the spin (= 1 2 ) chain model with alternating Heisenberg and Ising couplings to the case of anisotropic Heisenberg exchange. The model can be mapped to a bilinear fermion model, which is exactly solved via Jordan–Wigner and Bogoliubov transformations. We find low-energy excitations with a gap when the Ising coupling strength is not equal to 2. And this conclusion will not be changed for any kind of anisotropic Heisenberg exchange.

Anomalous isotope effect due to linear-energy-dependent electronic density of states in high-Tc superconductors

Abstract We have calculated the expression for Tc by using a linear-energy-dependent electronic density of states determined by tunneling experiments in Cu-O high-Tc superconductors. We find that the oxygen isotope exponent can be larger than standard BCS value 1 2 if the dominant attraction is due to the exchange of oxygen-phonon. With a joint mechanism, the anomalous isotope effect is qualitatively explained.

Hole tunneling through highly transparent symmetric double-barrier semiconductor structures

Using the transfer-matrix formalism, we investigate the tunneling of holes through symmetric double-barrier semiconductor structures with different heights of outer and inner edges. It is shown that, under appropriate conditions, a monotonic behavior (absence of resonant tunneling) occurs in the transmission coefficient in the absence or presence of the band mixing effect. Moreover, due to the band mixing effect, the monotonic behavior in all types of the transmission coefficient is only achievable when the resonant peak, related to the ground states of heavy holes in the corresponding potential well, disappears.

A possible reason of high Tc in oxide superconductor

Abstract We proposed that BCS-like Hamiltonian with quasi-two-dimensional tight-binding electrons describe the Ba-La-Cu-O system approximately. Tc was calculated under the cases both negligible and non-negligible weak coupling between neighbor layers. It is found that the results we obtained approach that of experiments.

Incommensurate domain walls in the two-dimensional Hubbard model with next-nearest-neighbor hopping

Abstract We present mean-field solutions of the incommensurate domain walls in the two-dimensional Hubbard model with next-nearest-neighbor (NNN) hopping terms. We found that the diagonal NNN hopping term t′ plays an important role in affecting the relative stabilities of the domain walls along the diagonal and axial directions on the square lattice. In contrast to previous well-known Hartree–Fock solution without t′ in which the diagonal stripe phase is stable with one hole on every site of the domain wall for U>4t, we find that the vertical stripe is more stable than the diagonal one for half hole occupation along the domain walls in the same parameter regime.

Surface excitations in anisotropic magnetic superlattices — Surface polaritons and spin waves

Abstract Surface magnetic polaritons and spin waves are examined in a unified framework for a promising kind of anisotropic FM/NM superlattices. Two types of the surface modes are classified, the coupled lower- surface modes and coupled standing waves. The modulation property of both the spectra and the envelop functions are discussed.

Collective excitations of a surface depleted layered electron gas

Abstract The transfer matrix method given by the authors [6] is developed for studying the collective excitations of a semi-infinite layered electron gas system with a defect layer at the surface. The equations of collective excitations and the analytical formulas of the induced potential are derived for such a system.

Strain-induced effect on the superconducting transition temperature of La2−xSrxCuO4 films☆

Abstract We investigate the strain effect on the transition temperature T c of superconducting (001) La 2− x Sr x CuO 4 films. Calculations show that the values of T c of the films on SrLaAlO 4 substrates under compressive strain are always higher than those on SrTiO 3 under tensile strain. As the thickness reduced, the films grown on SrTiO 3 substrates exhibit a rapid reduction of T c , whereas the T c increases on SrLaAlO 4 substrates. The theoretical results are in good agreement with experiments.

Origin of unusually large Tc enhancement in PrBa2Cu3Oy under pressure

Abstract The recently discovered PrBa 2 Cu 3 O y superconductor possesses remarkable properties. The superconducting transition temperature T c has been found to exceed 100 K under a pressure over 8 GPa and still have a pontential increase. We show that the extended t - J model with d -wave pairing for high- T c superconductivity can explain the unusual pressure dependence of T c in PrBa 2 Cu 3 O y by taking into account the variations of the hole concentration in the CuO 2 planes and the effective interaction with pressure. We suggest further experiments to enhance T c at ambient pressure in PrBa 2 Cu 3 O y .

Results of relaxation function theory for the NMR measurements in La2CuO4

Abstract The spin-lattice relaxation rates and the spin-echo decay rates for the two-dimensional Heisenberg model are interpreted in a framework of a self-consistent relaxation function theory. The results are compared with the experiments on La2CuO4 and the numerical simulations of quantum Monte Carlo method.