Magnetocaloric Effect of Topological Excitations in Kitaev Magnets

TL;DR

This paper explores using fractional excitations in quantum spin liquids, specifically Kitaev magnets, to achieve magnetocaloric cooling, potentially surpassing traditional methods reliant on dilute magnetic ions.

Contribution

It demonstrates the magnetocaloric effect of topological excitations in Kitaev models using tensor-network calculations, revealing strong cooling effects linked to spin fractionalization.

Findings

Strong demagnetization cooling due to $Z_2$ vortices in ferromagnetic Kitaev model

Discovery of a gapless QSL phase with high spin entropy in antiferromagnetic case

Potential for topological excitation cooling in Kitaev materials

Abstract

Traditional magnetic sub-Kelvin cooling relies on the nearly free local moments in hydrate paramagnetic salts, whose utility is hampered by the dilute magnetic ions and low thermal conductivity. Here we propose to use instead fractional excitations inherent to quantum spin liquids (QSLs) as an alternative, which are sensitive to external fields and can induce a very distinctive magnetocaloric effect. With state-of-the-art tensor-network approach, we compute low-temperature properties of Kitaev honeycomb model. For the ferromagnetic case, strong demagnetization cooling effect is observed due to the nearly free $Z_2$ vortices via spin fractionalization, described by a paramagnetic equation of state with a renormalized Curie constant. For the antiferromagnetic Kitaev case, we uncover an intermediate-field gapless QSL phase with very large spin entropy, possibly due to the emergence of spinon Fermi surface. Potential realization of topological excitation cooling in Kitaev materials is also discussed, which may offer a promising pathway to circumvent existing limitations in the paramagnetic hydrates.