Incipient and well-developed entropy plateaus in spin-S Kitaev models

TL;DR

This study investigates entropy and heat capacity in spin-S Kitaev models on a honeycomb lattice, revealing how anisotropy induces entropy plateaus at specific values, with implications for understanding quantum spin liquids.

Contribution

It demonstrates that anisotropy causes well-developed entropy plateaus at half the entropy of a two-level system for all spins greater than 1/2, and identifies an incipient plateau in isotropic cases.

Findings

Anisotropy induces entropy plateaus at 0.5*ln(2) for all S>1/2.

Isotropic models show an incipient plateau at half of maximum entropy.

Results are obtained using high-temperature series expansions and TPQ methods.

Abstract

We present results on entropy and heat-capacity of the spin-S honeycomb-lattice Kitaev models using high-temperature series expansions and thermal pure quantum (TPQ) state methods. We study models with anisotropic couplings $J_z=1\ge J_x=J_y$ for spin values 1/2, 1, 3/2, and 2. We show that for $S>1/2$, any anisotropy leads to well developed plateaus in the entropy function at an entropy value of $\frac{1}{2}\ln{2}$, independent of $S$. However, in the absence of anisotropy, there is an incipient entropy plateau at $S_{max}/2$, where $S_{max}$ is the infinite temperature entropy of the system. We discuss possible underlying microscopic reasons for the origin and implications of these entropy plateaus.