Magnetocaloric effect in quantum spin-s chains

TL;DR

This paper investigates the magnetocaloric effect in quantum spin-s chains, demonstrating cooling via magnetic field manipulation and revealing linear scaling near saturation, using exact diagonalization and Quantum Monte Carlo methods.

Contribution

It introduces a new method for computing low-lying excited states and provides detailed analysis of the magnetocaloric effect in various spin-s chains.

Findings

Cooling by closing the Haldane gap in spin-1 chains.

Linear scaling of the magnetocaloric effect with spin s near saturation.

Development of a Lanczos recursion-based method for excited states.

Abstract

We compute the entropy of antiferromagnetic quantum spin-s chains in an external magnetic field using exact diagonalization and Quantum Monte Carlo simulations. The magnetocaloric effect, i.e., temperature variations during adiabatic field changes, can be derived from the isentropes. First, we focus on the example of the spin-s=1 chain and show that one can cool by closing the Haldane gap with a magnetic field. We then move to quantum spin-s chains and demonstrate linear scaling with $s$ close to the saturation field. In passing, we propose a new method to compute many low-lying excited states using the Lanczos recursion.