ar X iv : c on d - m at / 9 41 00 16 v 1 6 O ct 1 99 4 PHASE TRANSITIONS OF FRUSTRATED XY SPINS IN TWO DIMENSIONS

ar X iv : c on d - m at / 9 51 10 70 v 1 1 4 N ov 1 99 5 Phase Transitions of the Bilayered Spin - S Heisenberg Model and Its Extension to Fractional Dimensions

We study the ground state and the phase transitions of the bilayered spinS antiferromagnetic Heisenberg model using the Schwinger boson mean field theory. The interplane coupling initially stabilizes but eventually destroys the long-range antiferromagnetic order. The transition to the disordered state is continuous for small S, and first order for large S. The latter is consistent with an argum...

ar X iv : c on d - m at / 9 31 00 59 v 1 2 6 O ct 1 99 3 Formation of Space - Time Structure in a Forest - Fire Model

PACS numbers: 05.

ar X iv : a lg - g eo m / 9 41 00 29 v 1 2 7 O ct 1 99 4 Contractions on a manifold polarized by an ample vector bundle

ar X iv : c on d - m at / 9 60 31 90 v 1 2 9 M ar 1 99 6 The Four - Dimensional XY Spin Glass

ar X iv : c on d - m at / 9 31 00 47 v 1 2 0 O ct 1 99 3 Statistical Mechanics of Vortices in Type - II Superconductors

Thermal fluctuations and disorder play an essential role in high-Tc superconductors. After reviewing the mean-field phase diagram we describe significant modifications that result when the effects of finite temperature and disorder are incorporated. Thermal fluctuations cause the melting of the Abrikosov flux line lattice into a vortex liquid at high temperatures, and disorder produces novel gl...