Thermal Hall conductivity in the cuprate Mott insulators Nd2CuO4 and Sr2CuO2Cl2

Marie-Eve Boulanger,W N Hardy,Maxime Dion,Gaël Grissonnanche,Andréanne Allaire,Sven Badoux,R Liang,X H Chen,D A Bonn,C H Wang,Anaëlle Legros,Louis Taillefer,Adrien Gourgout,Étienne Lefrançois

doi:10.1038/s41467-020-18881-z

Abstract

The heat carriers responsible for the unexpectedly large thermal Hall conductivity of the cuprate Mott insulator La2CuO4 were recently shown to be phonons. However, the mechanism by which phonons in cuprates acquire chirality in a magnetic field is still unknown. Here, we report a similar thermal Hall conductivity in two cuprate Mott insulators with significantly different crystal structures and magnetic orders – Nd2CuO4 and Sr2CuO2Cl2 – and show that two potential mechanisms can be excluded – the scattering of phonons by rare-earth impurities and by structural domains. Our comparative study further reveals that orthorhombicity, apical oxygens, the tilting of oxygen octahedra and the canting of spins out of the CuO2 planes are not essential to the mechanism of chirality. Our findings point to a chiral mechanism coming from a coupling of acoustic phonons to the intrinsic excitations of the CuO2 planes.

Highlights

The heat carriers responsible for the unexpectedly large thermal Hall conductivity of the cuprate Mott insulator La2CuO4 were recently shown to be phonons
The thermal Hall effect has become a useful probe of insulators[1], because it can reveal whether the carriers of heat in a material have chirality. (Here we use the term “chirality” to mean handedness in the presence of a magnetic field.) In insulators, the carriers of heat are not charged, but neutral, and so the electrical Hall effect is zero
The question is: what makes the phonons in cuprates become chiral? In order to provide answers to this question, we have investigated two other cuprate Mott insulators, Nd2CuO4 and Sr2CuO2Cl2, and find in both a large negative thermal Hall conductivity similar to that of La2CuO4

Summary

Introduction

The heat carriers responsible for the unexpectedly large thermal Hall conductivity of the cuprate Mott insulator La2CuO4 were recently shown to be phonons. In La2CuO4, at p = 0, the thermal Hall signal was found to be just as large as for an in-plane heat current, i.e., κzy(T) ≈ κxy(T)

Results

Conclusion