Bragg-Bose glass phase in vortex states of high-TcT_{\rm c} superconductors with sparse and weak columnar defects

Phase diagram of vortex states of high-$T_{\rm c}$ superconductors with {\it sparse and weak} columnar defects is obtained by large-scale Monte Carlo simulations of the three-dimensional anisotropic, frustrated XY model. The Bragg-Bose glass phase characterized by hexagonal Bragg spots and the diverging tilt modulus is observed numerically for the first time at low density of columnar defects. As the density of defects increases, the melting temperature increases owing to "selected pinning" of flux lines. When the density of defects further increases, the transition to the Bose glass phase occurs. The interstitial liquid region is observed between these two glass phases and the vortex liquid phase.Comment: using RevTex4, 4 pages, 8 figures (5 captions

Effects of point defects on the phase diagram of vortex states in high-Tc superconductors in B//c axis

The phase diagram for the vortex states of high-$T_{\rm c}$ superconductors with point defects in $\vec{B} \parallel c$ axis is drawn by large-scale Monte Carlo simulations. The vortex slush (VS) phase is found between the vortex glass (VG) and vortex liquid (VL) phases. The first-order transition between this novel normal phase and the VL phase is characterized by a sharp jump of the density of dislocations. The first-order transition between the Bragg glass (BG) and VG or VS phases is also clarified. These two transitions are compared with the melting transition between the BG and VL phases.Comment: 4 pages, 9 eps figures (included in text), uses revtex.sty, overall changes with several additional data points, though conclusion is unchange

Analysis on flow around a sphere at high mach number, low Reynolds number and adiabatic condition for high accuracy analysis of gas particle flows

This study analyses gas particle flow around a sphere under an adiabatic condition at high Mach number and low Reynolds number by direct numerical simulation of the three– dimensional compressible Navier–Stokes equation to investigate flow properties. The calculation was performed on a boundary-fitted coordinate system with a high-order scheme of sufficient accuracy. Analysis is conducted by assuming a rigid sphere with a Reynolds number based on the diameter of the sphere, and the free-stream velocity set between 50 and 300 and a free-stream Mach number set between 0.3 and 2.0. The effect of the Mach number on the flow properties and drag coefficient are discussed. The calculation shows the following results: 1) unsteady fluctuation of the hydrodynamic force becomes smaller as the Mach number increases, 2) the drag coefficient increases along with the Mach number due to an increase in the pressure drag by the shock-wave, and 3) an accurate prediction of the drag coefficient in the supersonic regime using traditional models might be difficult

Generic phase diagram of active polar films

We study theoretically the phase diagram of compressible active polar gels such as the actin network of eukaryotic cells. Using generalized hydrodynamics equations, we perform a linear stability analysis of the uniform states in the case of an infinite bidimensional active gel to obtain the dynamic phase diagram of active polar films. We predict in particular modulated flowing phases, and a macroscopic phase separation at high activity. This qualitatively accounts for experimental observations of various active systems, such as acto-myosin gels, microtubules and kinesins in vitro solutions, or swimming bacterial colonies.Comment: 4 pages, 1 figur

Ground-State Phase Diagram of the Two-Dimensional Quantum Heisenberg Mattis Model

The two-dimensional $S=1/2$ asymmetric Heisenberg Mattis model is investigated with the exact diagonalization of finite clusters. The N\'eel order parameter and the spin glass order parameter can be smoothly extrapolated to the thermodynamic limit in the antiferromagnetic region, as in the pure Heisenberg antiferromagnet. The critical concentration of the N\'eel phase is consistent with that of the two-dimensional Ising Mattis model, and the spin glass order parameter increases monotonously as the ferro-bond concentration increases. These facts suggest that quantum fluctuation does not play an essential role in two-dimensional non-frustrated random spin systems. KEYWORDS: quantum spin system, ground state, randomness, Mattis model, N\'eel order, spin glass orderComment: 10 pages, LaTeX, 6 compressed/uuencoded postscript figures, J. Phys. Soc. Jpn. 65 (1996) No. 2 in pres

Nonequilibrium Phase Transitions of Vortex Matter in Three-Dimensional Layered Superconductors

Large-scale simulations on three-dimensional (3D) frustrated anisotropic XY model have been performed to study the nonequilibrium phase transitions of vortex matter in weak random pinning potential in layered superconductors. The first-order phase transition from the moving Bragg glass to the moving smectic is clarified, based on thermodynamic quantities. A washboard noise is observed in the moving Bragg glass in 3D simulations for the first time. It is found that the activation of the vortex loops play the dominant role in the dynamical melting at high drive.Comment: 3 pages,5 figure

Infinitesimal incommensurate stripe phase in an axial next-nearest-neighbor Ising model in two dimensions

An axial next-nearest-neighbor Ising (ANNNI) model is studied by using the non-equilibrium relaxation method. We find that the incommensurate stripe phase between the ordered phase and the paramagnetic phase is negligibly narrow or may vanish in the thermodynamic limit. The phase transition is the second-order transition if approached from the ordered phase, and it is of the Kosterlitz-Thouless type if approached from the paramagnetic phase. Both transition temperatures coincide with each other within the numerical errors. The incommensurate phase which has been observed previously is a paramagnetic phase with a very long correlation length (typically $\xi\ge 500$). We could resolve this phase by treating very large systems ($\sim 6400\times 6400$), which is first made possible by employing the present method.Comment: 12 pages, 10 figures. To appear in Phys.Rev.

A quantum Monte Carlo algorithm realizing an intrinsic relaxation

We propose a new quantum Monte Carlo algorithm which realizes a relaxation intrinsic to the original quantum system. The Monte Carlo dynamics satisfies the dynamic scaling relation $\tau\sim \xi^z$ and is independent of the Trotter number. Finiteness of the Trotter number just appears as the finite-size effect. An infinite Trotter number version of the algorithm is also formulated, which enables us to observe a true relaxation of the original system. The strategy of the algorithm is a compromise between the conventional worldline local flip and the modern cluster loop flip. It is a local flip in the real-space direction and is a cluster flip in the Trotter direction. The new algorithm is tested by the transverse-field Ising model in two dimensions. An accurate phase diagram is obtained.Comment: 9 pages, 4 figure