Supersymmetric $t$-$J$ models with long-range interactions: thermodynamics and criticality

TL;DR

This paper studies the thermodynamics and critical phenomena of a supersymmetric long-range $t$-$J$ model, revealing multiple ground state phases, spin-charge separation, and diverse critical behaviors using a novel transfer matrix approach.

Contribution

It introduces a transfer matrix method to analyze supersymmetric $t$-$J$ models, providing exact thermodynamic expressions and uncovering complex critical behaviors beyond traditional techniques.

Findings

Identified five ground state phases in the su(2) case.

Confirmed spin-charge separation at all orders in low-temperature expansion.

Discovered various critical behaviors, including non-critical, critical with c=1, and c=3/2 phases.

Abstract

We analyze the thermodynamics and the critical behavior of the supersymmetric su($m$) $t$-$J$ model with long-range interactions. Using the transfer matrix formalism, we obtain a closed-form expression for the free energy per site both for a finite number of sites and in the thermodynamic limit. Our approach, which is different from the usual ones based on the asymptotic Bethe ansatz and generalized exclusion statistics, can in fact be applied to a large class of models whose spectrum is described in terms of supersymmetric Young tableaux and their associated Haldane motifs. In the simplest and most interesting su(2) case, we identify the five ground state phases of the model and derive the complete low-temperature asymptotic series of the free energy per site, the magnetization and charge densities, and their susceptibilities. We verify the model's characteristic spin-charge separation at low temperatures, and show that it holds to all orders in the asymptotic expansion. Using the low-temperature asymptotic expansions of the free energy, we also analyze the critical behavior of the model in each of its ground state phases. While the standard su(1|2) phase is described by two independent CFTs with central charge $c=1$ in correspondence with the spin and charge sectors, we find that the low-energy behavior of the su(2) and su(1|1) phases is that of a single $c=1$ CFT. We show that the model exhibits an even richer behavior on the boundary between zero-temperature phases, where it can be non-critical but gapless, critical in the spin sector but not in the charge one, or critical with central charge $c=3/2$.