Finite-temperature investigation of quarter filled ladder systems

We investigate charge ordering in a quarter-filled ladder at finite temperature by determinantal Quantum Monte Carlo. The sign problem is moderate in a wide range of model parameters relevant for NaV2O5. The charge order parameter exhibits a crossover as a function of inverse temperature beta on finite systems. Above a critical nearest neighbor Coulomb repulsion V-c, the correlation length grows exponentially with beta, indicative of the ordered phase at beta = infinity. We find a clear single-particle gap manifesting itself in a flat n(mu) dependence at large nearest neighbor Coulomb repulsion V. (c) 2005 Elsevier B.V. All rights reserved.