Ising-type quantum spin liquid state in PrMgAl11O19

We have grown single crystals of PrMgAl11O19, 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 the system. (iii) The ultralow-temperature thermal conductivity exhibits negligibly small residual term (kappa(0)/T ) and strong spin-phonon scattering effect, suggesting that the spin excitations are also involved. Our results further demonstrate that PrMgAl11O19 is a rare quantum spin liquid candidate with Ising-like anisotropy.