Finite-temperature phase structures of hard-core bosons in an optical lattice with an effective magnetic field

We study finite-temperature phase structures of hard-core bosons in a two-dimensional optical lattice subject to an effective magnetic field by employing the gauged CP$^1$ model. Based on the extensive Monte Carlo simulations, we study their phase structures at finite temperatures for several values of the magnetic flux per plaquette of the lattice and mean particle density. Despite the presence of the particle number fluctuation, the thermodynamic properties are qualitatively similar to those of the frustrated XY model with only the phase as a dynamical variable. This suggests that cold atom simulators of the frustrated XY model are available irrespective of the particle filling at each site.Comment: 13 pages, 9 figure

Finite-temperature phase diagram of two-component bosons in a cubic optical lattice: Three-dimensional t-J model of hard-core bosons

We study the three-dimensional bosonic t-J model, i.e., the t-J model of "bosonic electrons", at finite temperatures. This model describes the $s={1 \over 2}$ Heisenberg spin model with the anisotropic exchange coupling $J_{\bot}=-\alpha J_z$ and doped {\it bosonic} holes, which is an effective system of the Bose-Hubbard model with strong repulsions. The bosonic "electron" operator $B_{r\sigma}$ at the site $r$ with a two-component (pseudo-)spin $\sigma (=1,2)$ is treated as a hard-core boson operator, and represented by a composite of two slave particles; a "spinon" described by a Schwinger boson (CP$^1$ boson) $z_{r\sigma}$ and a "holon" described by a hard-core-boson field $\phi_r$ as $B_{r\sigma}=\phi^\dag_r z_{r\sigma}$. By means of Monte Carlo simulations, we study its finite-temperature phase structure including the $\alpha$ dependence, the possible phenomena like appearance of checkerboard long-range order, super-counterflow, superfluid, and phase separation, etc. The obtained results may be taken as predictions about experiments of two-component cold bosonic atoms in the cubic optical lattice.Comment: 8 pages, 14 figures, Size of figures has been adjuste

Vortex formation of a Bose-Einstein condensate in a rotating deep optical lattice

We study the dynamics of vortex nucleation and lattice formation in a Bose--Einstein condensate in a rotating square optical lattice by numerical simulations of the Gross--Pitaevskii equation. Different dynamical regimes of vortex nucleation are found, depending on the depth and period of the optical lattice. We make an extensive comparison with the experiments by Williams {\it et al.} [Phys. Rev. Lett. {\bf 104}, 050404 (2010)], especially focusing on the issues of the critical rotation frequency for the first vortex nucleation and the vortex number as a function of rotation frequency.Comment: 7 pages, 5 figure

Polarization envelope helicity dependent photovoltage in GaAs/Al03Ga07As modulation-doped quantum well

In this study, we demonstrate the switching of the direction of the photocurrent in an n-type GaAs/Al0.3Ga0.7As modulation-doped quantum well using a polarization pulse-shaping apparatus containing a 4f setup. The right- and left-polarization-twisting pulses with a polarization rotation frequency in the THz-regime are incident on a modulation-doped quantum well. The results show that the sign of the photovoltage is dependent on the direction of rotation of the polarization-twisting pulses, which can be explained by the circular photogalvanic effect combined with the production of a classical edge photocurrent from the acceleration of free electrons in the vicinity of the sample edge by the incident optical electric field. The wide range over which the polarization-rotation frequency may be tuned makes this method a powerful tool to investigate the response of an extensive variety of materials in the THz-regime