# Giant thermal Hall conductivity from neutral excitations in the pseudogap phase of cuprates

## TL;DR

This study reveals a large negative thermal Hall conductivity in the pseudogap phase of cuprates, likely caused by neutral excitations with spin chirality, suggesting exotic quantum states akin to spin liquids.

## Contribution

It provides evidence of a significant thermal Hall effect in the pseudogap phase, indicating the presence of neutral excitations and advancing understanding of this mysterious phase.

## Key findings

- Large negative thermal Hall conductivity appears at the pseudogap onset.
- The effect persists in insulating states, ruling out charge carriers.
- The phenomenon is attributed to neutral excitations with spin chirality.

## Abstract

The nature of the pseudogap phase of cuprates remains a major puzzle. Although there are indications that this phase breaks various symmetries, there is no consensus on its fundamental nature. Although Fermi-surface, transport and thermodynamic signatures of the pseudogap phase are reminiscent of a transition into a phase with antiferromagnetic order, there is no evidence for an associated long-range magnetic order. Here we report measurements of the thermal Hall conductivity $\kappa_{\rm xy}$ in the normal state of four different cuprates (Nd-LSCO, Eu-LSCO, LSCO, and Bi2201) and show that a large negative $\kappa_{\rm xy}$ signal is a property of the pseudogap phase, appearing with the onset of that phase at the critical doping $p^*$. Since it is not due to charge carriers -- as it persists when the material becomes an insulator, at low doping -- or magnons -- as it exists in the absence of magnetic order -- or phonons -- since skew scattering is very weak, we attribute this $\kappa_{\rm xy}$ signal to exotic neutral excitations, presumably with spin chirality. The thermal Hall conductivity in the pseudogap phase of cuprates is reminiscent of that found in insulators with spin-liquid states. In the Mott insulator LCO, it attains the highest known magnitude of any insulator.

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Source: https://tomesphere.com/paper/1901.03104