Possible gapless quantum spin liquid behavior in the triangular-lattice Ising antiferromagnet <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>PrMgAl</mml:mi><mml:mn>11</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>19</mml:mn></mml:msub></mml:mrow></mml:math>
Zhen Ma, Shuhan Zheng, Yingqi Chen, Ruokai Xu, Zhao-Yang Dong, Jinghui Wang, Hong Du, Jan Peter Embs, Shuaiwei Li, Yao Li, Yongjun Zhang, Meifeng Liu, Ruidan Zhong, Jun‐Ming Liu, Jinsheng Wen
Abstract
Quantum spin liquids (QSLs) represent a novel state where spins are highly entangled but do not order even at zero temperature due to strong quantum fluctuations. Such a state is mostly studied in Heisenberg models defined on geometrically frustrated lattices. Here, we turn to a new triangular-lattice antiferromagnet ${\mathrm{PrMgAl}}_{11}{\mathrm{O}}_{19}$, in which the interactions are believed to be of Ising type. Magnetic susceptibility measured with an external field along the $c$ axis is two orders of magnitude larger than that with a field in the $ab$ plane, displaying an ideal easy-axis behavior. Meanwhile, there is no magnetic phase transition or spin freezing observed down to 1.8 K. Ultralow-temperature specific heat measured down to 50 mK does not capture any phase transition either, but a hump at 4.5 K, below which the magnetic specific heat exhibits a quasiquadratic temperature dependence that is consistent with a Dirac QSL state. The inelastic neutron scattering technique is also employed to elucidate the nature of its ground state. In the magnetic excitation spectra, there is a gapless broad continuum at the base temperature 55 mK, in favor of the realization of a gapless QSL. Our results provide a scarce example for the QSL behaviors observed in an Ising-type magnet, which can serve as a promising platform for future research on QSL physics based on an Ising model.