Quantum Supercritical Regime with Universal Magnetocaloric Scaling in Ising Magnets

TL;DR

This paper introduces a novel quantum supercritical regime in Ising magnets, characterized by universal magnetocaloric scaling and potential applications in low-temperature cooling, expanding understanding of quantum critical phenomena.

Contribution

It proposes a new quantum supercritical regime controlled by longitudinal field and demonstrates its universal scaling and magnetocaloric effects through thermal tensor network simulations.

Findings

Quantum supercritical regime enclosed by finite-temperature crossover boundaries.

Universal magnetocaloric scaling with diverging Grüneisen ratio.

Potential for millikelvin cooling using supercritical magnetocaloric effect.

Abstract

Quantum critical points ubiquitously emerge in strongly correlated systems, with their influence persisting at finite temperatures and external fields. A paradigmatic example is the quantum Ising magnet, where transverse field $g$ controlling quantum fluctuations can expand the quantum critical point into an extended quantum critical regime. In this work, we propose a distinct quantum supercritical regime originating also from the quantum critical point but controlled by the longitudinal field $h$ coupled to the order parameter. Through thermal tensor network simulations, we find the quantum supercritical regime is enclosed by the finite-temperature crossover boundaries $T \propto h^{{z\nu}/\Delta}$, where $z$, $\nu$ and $\Delta \equiv \beta+\gamma$ are critical exponents. We comprehend the supercritical scaling via thermal data collapse based on the derived scaling form. Amongst other intriguing phenomena in quantum supercritical regime, there exists an enhanced magnetocaloric effect characterized by a universally diverging magnetic Gr\"uneisen ratio $\Gamma_h \propto T^{-\Delta/{z\nu}}$, which indicates that a small symmetry-breaking field $h$ can generate dramatic temperature variation. We propose to observe the quantum supercritical regime in Ising-chain compound CoNb$_2$O$_6$ and related quantum materials, revealing a helium-3-free pathway to millikelvin cooling via the supercritical magnetocaloric effect.