Finite-temperature behavior of a classical spin-orbit-coupled model for YbMgGaO4 with and without bond disorder

Abstract

We present the results of finite-temperature classical Monte Carlo simulations of a strongly spinorbit-coupled nearest-neighbor triangular-lattice model for the candidate U(1) quantum spin liquid YbMgGaO 4 at large system sizes. We find a single continuous finite-temperature stripe-ordering transition with slowly diverging heat capacity that completely breaks the sixfold ground-state degeneracy, despite the absence of a known conformal field theory describing such a transition. We also simulate the effect of random-bond disorder in the model, and find that even weak bond disorder destroys the transition by fragmenting the system into very large domains -possibly explaining the lack of observed ordering in the real material. The Imry-Ma argument only partially explains this fragility to disorder, and we extend the argument with a physical explanation for the preservation of our system's time-reversal symmetry even under a disorder model that preserves the same symmetry. arXiv:1801.06941v3 [cond-mat.str-el] 11 May 2018 -1.0 -0.5 0.5 1.0 J ±± J zz 0.25 0.5 0.75

Hierarchy of Exchange Interactions in the Triangular-Lattice Spin Liquid YbMgGaO4

“…Because of their nonspin-conserving nature, dominant pseudodipolar interactions should manifest as an asymptotic approach to saturated magnetization, as recently observed in the candidate Kitaev spin liquid α-RuCl 3 [81]. Finally, we note that the role and extent of CEF and exchange disorder remains an outstanding issue in YbMgGaO 4 with possible impact ranging from the mimicry of a spin liquid [47,48,82,83] to disorder-induced entanglement [84][85][86].…”

“…We note, however, that subleading pseudodipolar interactions are also necessary to best explain our data. When combined with the likely presence of exchange disorder due to Mg 2þ and Ga 3þ disorder, this makes the spin-liquid mimicry [47,48,82] or the J 1 − J 2 quantum spin-liquid [36][37][38] mechanisms serious contenders to the various scenarios proposed to explain the physics of YbMgGaO 4 thus far [44,62,63].…”

YbMgGaO4: A Triangular‐Lattice Quantum Spin Liquid Candidate

“…First of all, the observed QSL GS or at least the quantum disordered behaviors of YbMgGaO 4 have to be understood. The first important ingredient is the anisotropy of the effective spin‐1/2 Hamiltonian caused by the strong spin–orbit entanglement of Yb 3+ , which makes the system localize around the phase boundary between the 120 o and two stripe collinear Néel states, and makes the order very fragile against the quantum fluctuations . While the observed GS properties may be hard to be fully understood by only considering the NN anisotropic (in the spin space) spin Hamiltonian .…”

Spin liquids in geometrically perfect triangular antiferromagnets

“…The peak of the spectral weight at the M -point led to an idea that the ground state of YbMgGaO 4 may be a melted stripe order, where stripes are stabilized by the sizable J 2 , but their directions are random under a change in the sign of J ±± 1 [136] or a variation of all exchange parameters throughout the crystal [137], the latter scenario being consistent with the predictions of the superexchange theory [117]. Both types of disorder lead to a liquid-like classical phase, although it remains unclear whether excitations of this random stripe state [136] may be responsible for the peculiar spin dynamics observed experimentally (Sec.…”