Gapped quantum spin liquid in a triangular-lattice Ising-type antiferromagnet PrMgAl11O19

TL;DR

This study identifies PrMgAl11O19 as a gapped Z2 quantum spin liquid in a triangular-lattice Ising antiferromagnet, using specific heat and thermal conductivity measurements to reveal its unique magnetic excitations.

Contribution

It provides experimental evidence for a gapped Z2 quantum spin liquid ground state in an Ising-type triangular-lattice antiferromagnet, a previously elusive phase.

Findings

Magnetic specific heat shows quadratic temperature dependence.

No mobile gapless fermionic excitations detected.

Phonons strongly scattered by magnetic excitations, indicating a gapped state.

Abstract

In the search of quantum spin liquid (QSLs), spin-1/2 triangular-lattice Heisenberg antiferromagnets (TLHAFs) have always been viewed as fertile soils. Despite the true magnetically-ordered ground state, anisotropy has been considered to play a significant role in stabilizing a QSL state. However, the nature and ground state of the most anisotropic case, the triangular-lattice Ising antiferromagnet (TLIAF), remains elusive and controversial. Here, we report specific heat and thermal conductivity measurements on a newly-discovered Ising-type QSL candidate PrMgAl11O19. At zero field, the magnetic specific heat shows a quadratic temperature dependence. On the contrary, no direct positive magnetic contribution to thermal conductivity was detected, ruling out the presence of mobile gapless fermionic excitations. Further analysis of phonon thermal conductivity reveals that the phonons are strongly scattered by thermally-activated magnetic excitations out of a gap, which exhibits a linear dependence with magnetic field. These results demonstrate that the spin-1/2 TLIAF PrMgAl11O19 has a gapped Z2 QSL ground state.