Ising-type quantum spin liquid state in PrMgAl${}_{11}$O${}_{19}$

Abstract

We have grown single crystals of PrMgAl${}_{11}$O${}_{19}$, an ideal triangular-lattice antiferromagnet, and performed magnetic susceptibility, specific heat and thermal conductivity measurements at low temperatures. The main results are as follows: (i) The temperature-dependent susceptibility shows a negligible in-plane response and the isothermal magnetization curves confirm the easy axis along the $c$ axis. (ii) The specific heat measurements reveal the absence of long-range magnetic order down to 60 mK, and the power-law temperature dependence indicates the existence of the gapless magnetic excitations in system. (iii) The ultralow-temperature thermal conductivity exhibits negligibly small residual term ($\hat{I}{º}_0/T$) and strong spin-phonon scattering effect, suggesting that the spin excitations are also involved. Our results further demonstrate that PrMgAl${}_{11}$O${}_{19}$ is a rare quantum spin liquid candidate with Ising-like anisotropy.

8 pages, 5 figures