Thermodynamic properties of an $S=1/2$ ring-exchange model on the triangular lattice

TL;DR

This study investigates the thermodynamic behavior of an $S=1/2$ triangular lattice model with ring-exchange interactions, revealing a double-peak specific heat and non-magnetic excitations for certain interaction ratios.

Contribution

It introduces a numerical approach to analyze thermodynamic properties of a triangular lattice model with ring-exchange, highlighting new features like double-peak specific heat and non-magnetic excitations.

Findings

Double-peak structure in specific heat for $J_c/J \gtrsim 0.04$

Existence of non-magnetic excitations below magnetic ones

Thermodynamic signatures of ring-exchange interactions

Abstract

By using a numerically exact diagonalization technique and a block-extended version of the finite-temperature Lanczos method, we study thermodynamic properties of an $S=1/2$ Heisenberg model on the triangular lattice with an antiferromagnetic nearest-neighbor interaction $J$ and a four-spin ring-exchange interaction $J_{\rm c}$. Calculations are performed on small clusters under the periodic-boundary conditions. In contrast to the purely triangular case with $J_{\rm c}=0$, the specific heat exhibits a characteristic double-peak structure for $J_{\rm c}/J \gtrsim 0.04$. From the calculation of the entropy and the uniform magnetic susceptibility, it is shown that non-magnetic excitations exist below the magnetic excitation for $J_{\rm c}/J \gtrsim 0.04$.