Quantum fluctuations are expected to lead to highly entangled spin-liquid states in certain two-dimensional spin-1/2 compounds. We have synthesized and measured thermodynamic properties and muon spin relaxation rates in the copper-based two-dimensional triangular-lattice spin liquids Lu3Cu2Sb3O14 and Lu3CuZnSb3O14. The former is the least disordered of this kind discovered to date. Magnetic entropy generation at high temperatures has been ruled out after carefully correcting for the lattice specific heat. Surprisingly, roughly half of the magnetic entropy is missing down to temperatures of O(10−3) the exchange energy, independent of magnetic field up to gμBH≳kBΘW, where ΘW is the Weiss temperature. The magnetic specific heat divided by temperature CM(T)/T and muon spin relaxation rate λ(T) are both temperature-independent at low temperatures, followed by logarithmic decreases with increasing temperature. This behavior can be simply characterized by scale-invariant time-dependent fluctuations with a single parameter. Since no cooperative effects due to impurities are observed, the measured properties are intrinsic. They are evidence that in Lu3Cu2Sb3O14 massive quantum fluctuations lead to either a gigantic specific heat peak from singlet excitations at very low temperatures or, perhaps less likely, an extensively degenerate possibly topological singlet ground state.
@article{arxiv.2102.09271,
title = {Intrinsic new properties of a quantum spin liquid},
author = {Yanxing Yang and Xin Li and Cheng Tan and Zihao Zhu and Jian Zhang and Zhaofeng Ding and Qiong Wu and Changshen Chen and Toni Shiroka and Yuanhua Xia and Douglas E. MacLaughlin and Chandra M. Varma and Lei Shu},
journal= {arXiv preprint arXiv:2102.09271},
year = {2022}
}