THERMODYNAMICS OF THE GAUGE FIELD-THEORIES OF THE T-J MODEL

The thermodynamics and stability of the uniform resonating-valence-bond phase of the t-J model are studied using a lattice gauge field formulation. The free energy and entropy of this phase are compared to exact high-temperature expansion results. At the mean-field level the entropy is overestimated roughly by a factor of 2 and the free energy is less than half of the exact result. Including fluctuations of the gauge field in the random-phase approximation improves the free energy and entropy considerably. However, at dopings < 0.25 an instability of the uniform phase toward a flux-density-wave phase occurs with the transition temperature higher than approximately 0.3J.