Finite-Temperature Techniques

Peter Fulde

Peter Fulde

Andreas Nunnenkamp, J. N. Milstein, Keith R. Burnett

For a condensate in a one-dimensional ring geometry, we compare the thermodynamic properties of three conceptually different classical field techniques: stochastic dynamics, microcanonical molecular dynamics, and the ``classical field method.'' Starting from nonequilibrium initial conditions, all three methods approach steady states whose distribution and correlation functions are in excellent agreement with an exact evaluation of the partition function in the high-temperature limit. Our study helps to establish these various classical field techniques as powerful nonperturbative tools for systems at finite temperatures.

Jens O. Andersen, Michael T. Strickland

A homogeneous Bose gas is investigated at finite temperature using renormalization-group techniques. A nonperturbative flow equation for the effective potential is derived using sharp and smooth cutoff functions. Numerical solutions of these equations show that the system undergoes a second-order phase transition in accordance with universality arguments. We obtain the critical exponent $\ensuremath{\nu}=0.73.$

Michael Stone

Samir El Shawish, J. Bonča, Igor Sega

Using finite temperature Lanczos technique on finite clusters we calculate dynamical spin structure factor of the quasi-two-dimensional dimer spin liquid SrCu2(BO3)2 as a function of wavevector and temperature. Unusual temperature dependence of calculated spectra is in agreement with inelastic neutron scattering measurements. Normalized peak intensities of the single-triplet peak are q-independent, their unusual temperature dependence is analyzed in terms of thermodynamic quantities.