Numerical Evidence of Quantum Melting of Spin Ice: Quantum-to-Classical Crossover

Yasuyuki Kato, Shigeki Onoda
2015 Physical Review Letters  
Unbiased quantum Monte-Carlo simulations are performed on the nearest-neighbor spin-1/2 pyrochlore XXZ model with an antiferromagnetic longitudinal and a weak ferromagnetic transverse exchange couplings, J and J_. The specific heat exhibits a broad peak at T_CSI∼0.2J associated with a crossover to a classical Coulomb liquid regime showing a suppressed spin-ice monopole density, a broadened pinch-point singularity, and the Pauling entropy for |J_|≪ J, as in classical spin ice. On further
more » ... the entropy restarts decaying for J_>J_ c∼-0.104J, producing another broad specific heat peak for a crossover to a bosonic quantum Coulomb liquid, where the spin correlation contains both photon and quantum spin-ice monopole contributions. With negatively increasing J_ across J_ c, a first-order thermal phase transition occurs from the quantum Coulomb liquid to an XY ferromagnet. Relevance to magnetic rare-earth pyrochlore oxides is discussed.
doi:10.1103/physrevlett.115.077202 pmid:26317744 fatcat:27vwx6djfzei7dzmcyxrlkwzum