Enhanced thermal Hall effect in the square-lattice Néel state

Abstract

Recent experiments on several cuprate compounds have identified an enhanced thermal Hall response in the pseudogap phase. Most strikingly, this enhancement persists even in the undoped system, which challenges our understanding of the insulating parent compounds. To explain these surprising observations, we study the quantum phase transition of a squarelattice antiferromagnet from a confining Néel state to a state with coexisting Néel and semion topological order. The transition is driven by an applied magnetic field and involves no change in the symmetry of the state. The critical point is described by a strongly-coupled conformal field theory with an emergent global SO(3) symmetry. The field theory has four different formulations in terms of SU (2) or U (1) gauge theories, which are all related by dualities; we relate all four theories to the lattice degrees of freedom. We show how proximity of the confining Néel state to the critical point can explain the enhanced thermal Hall effect seen in experiment.

Topological phase transition and nontrivial thermal Hall signatures in honeycomb lattice magnets

“…Similar physics was also identified by the authors of Ref. [22] where they started from a π -flux QSL on a square lattice and studied the proximity behavior of critical point to explain the experimental observation of giant thermal Hall conductivity in the pseudogap phase of cuprate superconductors [23].…”

“…Given the suggestion of a CSL [15,21], we identify a topological phase transition with increasing magnetic fields. Specifically, we find a quantized thermal Hall effect in the coexisting phase and a nontrivially enhanced thermal Hall conductivity in the confining ordered phase near the quantum critical point, similar to the discussion in the context of unusual thermal Hall effect for pseudogap phase of copper-based superconductors [22,23]. The situation that we considered here would apply to the relevant quantum materials with multiple competing phases, where the interplay among conventional ordered states, fractionalized elementary excitations in QSLs and Zeeman coupling together drive the topological phase transition and result in nontrivial thermal Hall signatures.…”

Thermal Hall conductivity in the cuprate Mott insulators Nd2CuO4 and Sr2CuO2Cl2

“…Another avenue of investigation for cuprates is the possibility that they harbour exotic chiral excitations, like spinons 18 , 19 that could couple to phonons. Such a coupling has recently been considered for the case of Majorana fermions in a Kitaev spin liquid 28 .…”

“…Therefore, it must come either from spin-related excitations (possibly topological, as in refs. 18 , 19 ) or from phonons (as in ref. 15 ).…”

Emergent QCD3 quantum phase transitions of fractional Chern insulators

“…Motivated by the progress on the QED 3 -Chern-Simons universality class of the QH/CI transitions, here we go one step further to think about phase transitions described by the QCD 3 -Chern-Simons theory with emergent non-Abelian gauge fields. Similar to its QED 3 cousin, the QCD 3 -Chern-Simons theory also has interesting properties such as duality [39] and has generated considerable interest in the past [40][41][42][43][44][45][46][47]. In this paper, we mainly focus on two types of such phase transitions that can be understood using non-Abelian parton constructions [48].…”