Chen Yu-Guang

A Spin-Polarized Current Direction Controller Based on a Nonuniform Rashba Quantum Wire

A spin-polarized current direction controller scheme is proposed based on a nonuniform Rashba quantum wire. It is shown that |PLRz| = |PRLz|, whereas their signs are opposite, and the effect of this phenomenon is due to the two broken symmetries and the unbroken C2-rotation symmetry of the investigated system. In addition, the spin-polarized current is nonzero even with a strong disorder strength, which demonstrates that this structure may be utilized for potential applications.

Dynamical Process of Dissociation of Excitons in Polymer Chains with Impurities

Within an extended Su—Schrieffer—Heeger model including impurity interactions, the dynamical process of exciton dissociation in the presence of an external electric field is investigated by using a non-adiabatic evolution method. Under the action of impurities, the stability as well as the effective mass of the exciton is reduced. Our results show that the field required to dissociate the excitons depends sensitively on the strength of the impurity potential. As the impurity potential strength increases, the dissociation field decreases effectively. The theoretical results are expected to provide useful predictions concerning which polymers with properly impurity-assisted interactions are likely to be more suitable for use in organic solar cells.

Anisotropic Effects on Magnetoelastic Transition in Magnetic Molecular Rings

We numerically study the anisotropic effects on the magnetoelastic transition in an S = 1/2 XXZ model with a finite lattice number. It is found that the order of the magnetoelastic transition is strongly affected by the anisotropy parameter λ and there may exist a critical λc dividing the first-order transition and the continuous transition.

Critical behaviour of coupled organic ferromagnet chains

The interchain coupling in a model, which is most relevant to organic ferromagnets, is studied by a kind of mean field theory. A full phase diagram is given for this model. It is shown that the interchain coupling dramatically affects the ferromagnetic order in the ground state. When the interchain coupling reaches a critical value, the high-spin ground state disappears and the system may transit from ferromagnetic phase into Kondo-singlet phase.

Ground-State Properties of a Local Sine-Gordon Model with Two Frequencies

The local sine-Gordon model with two frequencies is studied by a variational method. The renormalization mass and classical field path are calculated. We find an Ising-like phase transition, which is analogous in the global sine-Gordon model with two frequencies. A full phase diagram is given.

The ground state properties of the S = 1/2 antiferromagnetic XY model with quasiperiodic modulation

The low-energy properties of the S = 1/2 antiferromagnetic XY model with quasiperiodic modulation are investigated for the consideration of spin–phonon coupling. It is found that the lattice distortion at every site displays a self-similar character, which is induced by quasiperiodic modulation. As quasiperiodic modulation is strengthened, the average lattice distortion may decrease and increase for strong and weak enough spin–phonon coupling, respectively. Correspondingly, the scaling behavior of the energy gap in this system is also strongly dependent on the spin–phonon coupling.

Magnetoelastic Instability in Ring-Shaped Molecule Magnets with Next-Nearest Neighbor Coupling

In considering next-nearest neighbor (NNN) coupling, we numerically investigate the magnetoelastic instability in ring-shaped mesoscopic antiferromagnetic Heisenberg spin 1/2 systems with spin-phonon interaction. The results indicate that, for antiferromagnetic NNN coupling J2, there may be a critical value Jc2, at which the ground state is dimerized for arbitrary lattice spring constant and beyond and below which the magnetoelastic instability behavior is different from each other. The values of Jc2 are irrelevant to the system size. For ferromagnetic NNN coupling, only continuous transition is present from dimerized phase to uniform phase as lattice spring constant is increased.

Spin-Flip Process of Polarons in Conjugated Polymers with Magnetic Impurities

Being driven by an external electric field, a polaron carrying both spin 1/2 and charge ±e moves at a constant speed in a polymer chain. When the polaron passes through a specific site, which couples to a magnetic impurity via spin-exchange interactions, its spin undergoes a spin-flip process if it is antiparallel to the impurity spin. Our numerical simulation shows that (a) a swap-like operation is performed between the polaron and impurity during the scattering process (b) polarons might be good candidates to be information carriers in the molecular scale.

Spin-dependent electron transport of a waveguide with Rashba spin--orbit coupling in an electromagnetic field

We investigate theoretically the spin-dependent electron transport in a straight waveguide with Rashba spin–orbit coupling (SOC) under the irradiation of a transversely polarized electromagnetic (EM) field. Spin-dependent electron conductance and spin polarization are calculated as functions of the emitting energy of electrons or the strength of the EM field by adopting the mode matching approach. It is shown that the spin polarization can be manipulated by external parameters when the strength of Rashba SOC is strong. Furthermore, a sharp step structure is found to exist in the total electron conductance. These results can be understood by the nontrivial Rashba subbands intermixing and the electron intersubband transition when a finite-range transversely polarized EM field irradiates a straight waveguide.

Scaling Properties of Energy Gap in Dimerized Spinless Fermion Chains with Quasiperiodic Modulation

By employing the exact diagonalization method, we investigate the low-energy behaviour of the dimerized spinless fermion chains with quasiperiodic modulation. It is found that for off-diagonal modulation, the energy gap with length N scales as exp(−cNω) with nonuniversal exponent ω if the dimerization is nonzero. However, for diagonal modulation, there may exist a critical dimerization δc beyond which the system exhibits a metal–insulator transition.