Enhanced thermal Hall effect in the square-lattice Néel state

• Published in: Nature physics Vol. 15; no. 12; pp. 1290 - 1294
• Main Authors: Samajdar, Rhine, Scheurer, Mathias S., Chatterjee, Shubhayu, Guo, Haoyu, Xu, Cenke, Sachdev, Subir
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.12.2019; Nature Publishing Group
• Subjects: 639/766/119/1003; 639/766/119/2792; 639/766/119/2794; 639/766/530/2795; Antiferromagnetism; Atomic; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Confining; Copper oxides; Critical point; Electromagnetism; Excitation; Field theory; Formulations; Gauge theory; Hall effect; Magnetic fields; Magnetism; Mathematical and Computational Physics; Molecular; Optical and Plasma Physics; Phase transitions; Physics; Physics and Astronomy; Symmetry; Theoretical
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/s41567-019-0669-3

Common wisdom about conventional antiferromagnets is that their low-energy physics is governed by spin–wave excitations. However, recent experiments on several cuprate compounds have challenged this concept. An enhanced thermal Hall response in the pseudogap phase was identified, which persists even in the insulating parent compounds without doping. Here, to explain these surprising observations, we study the quantum phase transition of a square-lattice 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 experiments. The remarkably large thermal Hall response recently observed in the copper oxides challenges our understanding of the excitations in an insulating antiferromagnet. Here, a possible explanation of the underlying physics is provided.