Shi Yun-Long

Frequency properties of the defect mode inside a photonic crystal band-gap with zero average refractive index

Left-handed metamaterial has been designed based on transmission line technology. A left-handed and a normal materials are studied alternately to form a one-dimensional photonic crystal with an average refractive index of zero but a special band-gap emerges. The two band-edge frequencies of this gap are insensitive to the incident angle and lattice constant. These characteristics can be used in the miniaturization of filters and high-quality coupling. Studies show that we can regulate the mode frequency by controlling the thickness of the defect layer, which can provide a method for the adjusting frequency in applications. The experimental results are consistent with numerical simulation.

The symmetric and antisymmetric superexchange interactions in spin-Peierls system

The influences of Dzyaloshinskii–Moriya (DM) interaction and Kaplan–Shekhtman–Entinwohlman–Aharony (KSEA) interaction on the dimerization of a spin-Peierls system are investigated theoretically by using the Lanczos numerical method. The ground state of the spin-Peierls system is still dimerized phase when both of the DM and the KSEA interactions have the same value with Heisenberg interaction. It is found that the KSEA interaction and uniform DM interaction are always against systemic dimerization, but the staggered DM interaction acts in favour of dimerization. Furthermore, the influences of the DM and the KSEA interactions are also studied in terms of the ground state index rate and the energy gap index rate of the dimerized Heisenberg system. The results show that the DM interaction makes the index rates larger, while the KSEA interaction makes them smaller.

Phase Diagram of One-Dimensional Bosons in an Array of Local Nonlinear Potentials at Zero Temperature

The Gaussian wave functional method is applied to a boson system with an array of local nonlinear potentials to study the phase diagram of its ground state. The stable ground state is determined by the renormalized mass which is a function of the parameter , the strength of potential and the potential concentration . In different cases and , can have different multiplicities, the phase diagram in parameter space is thus depicted. The value depends on the concentration , for , it coincides with that of the single impurity model; while coincides with the conclusion of the continuous model.

Ground state and elementary excitations of the Peierls-Hubbard model

The ground state and elementary excitations of the Peierls-Hubbard model are studied by using Gaussian wave functional method. The results show that the charge and spin degrees of freedom couple to each other due to the simultaneous existance of the dimerization and Hubbard repulsions. In the region of βs2 > 2π the spin gap ms is still present. Also the influence of Hubbard repulsions on the dimerization is derived from the critical behavior of ground state energy.