Thermal Hall Effect and Neutral Spinons in a Doped Mott Insulator

TL;DR

This paper models neutral spinons in doped Mott insulators to explain the thermal Hall effect observed in cuprates, linking topological gauge structures with experimental transport measurements in the pseudogap phase.

Contribution

It introduces a topological gauge theory describing neutral spinons' role in thermal Hall effects, providing a phenomenological framework consistent with experiments.

Findings

Neutral spinons contribute to thermal Hall effect via intrinsic transverse motion.

Transport coefficients depend on doping and $T_c$, matching experimental signs and trends.

The theory links spinon excitations to the pseudogap phase and phase transitions.

Abstract

In the pseudogap phase of the cuprate, a thermal Hall response of neutral objects has been recently detected experimentally, which continuously persists into the antiferromagnetic insulating phase. In this work, we study the transport properties of neutral spinons as the elementary excitation of a doped Mott insulator, which is governed by a mutual Chern-Simons topological gauge structure. We show that such a chiral spinon as a composite of an $S=1/2$ spin sitting at the core of a supercurrent vortex, can contribute to the thermal Hall effect, thermopower, and Hall effect due to its intrinsic transverse (cyclotron) motion under internal fictitious fluxes. In particular, the magnitudes of the transport coefficients are phenomenologically determined by two basic parameters: the doping concentration and $T_c$, quantitatively consistent with the experimental measurements including the signs and qualitative temperature and magnetic field dependence. Combined with the predictions of the spinon longitudinal transport properties, including the Nernst and spin Hall effects, a phenomenological description of the pseudogap phase is established as characterized by the neutral spinon excitations, which eventually become "confined" with an intrinsic superconducting transition at $T_c$. Finally, within this theoretical framework, the "order to order" phase transition between the superconducting and antiferromagnetic insulating phases are briefly discussed, with the thermal Hall monotonically increasing into the latter.