Su-Peng Kou

Coexistence of itinerant electrons and local moments in iron-based superconductors

In view of the recent experimental facts in the iron-pnictides, we make a proposal that the itinerant electrons and local moments are simultaneously present in such multiband materials. We study a minimal model composed of coupled itinerant electrons and local moments to illustrate how a consistent explanation of the experimental measurements can be obtained in the leading-order approximation. In this mean-field approach, the spin-density-wave (SDW) order and superconducting pairing of the itinerant electrons are not directly driven by the Fermi surface nesting, but are mainly induced by their coupling to the local moments with momentum match. The presence of the local moments as independent degrees of freedom naturally provides strong pairing strength for superconductivity and also explains the normal-state linear-temperature magnetic susceptibility above the SDW transition temperature. We show that this simple model is supported by various anomalous magnetic properties which are in quantitative agreement with experiments.

Quantum-classical phase transition of escape rates in biaxial spin particles

By using a stereographic projection of the unit sphere of magnetization vector onto a complex plane for the equations of motion, the effect of an external magnetic field for integrability of the system is discussed. The properties of the Jest solutions and the scattering data are then investigated through introducing transformations other than the Riemann surface in order to avoid double-valued functions of the usual spectral parameter. The exact multisoliton solutions are investigated by means of the Binet-Cauchy formula. The results showed that under the action of an external magnetic field nonlinear magnetization depends essentially on two parameters: its center moves with a constant velocity, while its shape changes with another constant velocity; its amplitude and width vary periodically with time, while its shape is also dependent on time and is unsymmetric with respect to its center. The orientation of the nonlinear magnetization in the plane orthogonal to the anisotropy axis changes with an external magnetic field. The total magnetic momentum and the integral of the motion coincident with its z component depend on time. The mean number of spins derivated from the ground state in a localized magnetic excitations is dependent on time. The asymptotic behavior of multisoliton solutions, the total displacement of center, and the phase shift of the jth peak an also analyzed. [S0163-1829(99)07121-0].

Mutual Chern-Simons theory for Z(2) topological order

We study several different

Chiral spin liquid in a correlated topological insulator

{Z}_{2}

Phase Diagram and a Possible Unified Description of Intercalated Iron Selenide Superconductors

topological ordered states in frustrated spin systems. The effective theories for those different

Magnetic and superconducting instabilities in a hybrid model of itinerant/localized electrons for iron pnictides

{Z}_{2}

Experimental implementation of adiabatic passage between different topological orders.

topological orders all have the same form---a

Spin Hall effect in a doped Mott insulator

{Z}_{2}

Topological gauge structure and phase diagram for weakly doped antiferromagnets

gauge theory which can also be written as a mutual

Quantum phases of the Bose-Hubbard model in optical superlattices

U(1)\ifmmode\times\else\texttimes\fi{}U(1)