The melting transition of vortex lattice in type-II superconductors with magnetic field perpendicular to the anisotropy axis is studied in the framework of the elastic theory. It is found that the thermal fluctuations in the two directions transverse to the magnetic field are approximately proportional to each other with the constant, different from the anisotropy parameter, in a wide portion of phase diagram. One can introduce two Lindemann numbers with the ratio determined by the thermal fluctuations to draw a single melting line. The melting line thus obtained fits the experimental phase boundary quite well.

The Ising-like phase transition of the two-dimensional fully frustrated XY model with weak positional disorder is studied in a short-time dynamic-scaling scheme. It is observed that the weak disorder does not destroy the Ising-like order. Besides the critical temperature, all the static and dynamic critical exponents are estimated.

No abstract

No abstract