Gapless triangular-lattice spin-liquid candidate in PrZnAl$_{11}$O$_{19}$

TL;DR

This study presents PrZnAl$_{11}$O$_{19}$ as a promising gapless quantum spin liquid candidate with a perfect 2D triangular lattice, exhibiting persistent spin fluctuations down to very low temperatures despite strong antiferromagnetic interactions.

Contribution

It provides experimental evidence of a gapless QSL in a nearly ideal triangular lattice, overcoming common material imperfections.

Findings

PrZnAl$_{11}$O$_{19}$ shows no magnetic order or freezing down to 50 mK.

The material exhibits persistent spin fluctuations despite strong antiferromagnetic couplings.

INS and specific heat data support a gapless quantum spin liquid state.

Abstract

A quantum spin liquid (QSL) is an exotic state in which electron spins are highly entangled, yet keep fluctuating even at zero temperature. Experimental realization of model QSLs has been challenging due to imperfections, such as antisite disorder, strain, and extra or a lack of interactions in real materials compared to the model Hamiltonian. Here we report the magnetic susceptibility, thermodynamic, inelastic neutron scattering (INS), and muon-spin relaxation studies on a polycrystalline sample of PrZnAl$_{11}$O$_{19}$, where the Pr$^{3+}$ ions form an ideal two-dimensional triangular lattice. Our results demonstrate that this system does not order nor freeze, but keep fluctuating down to 50 mK despite large antiferromagnetic couplings ($\sim$ -10 K). Furthermore, the INS and specific-heat data suggest that PrZnAl$_{11}$O$_{19}$ is best described as a gapless QSL.