Pomeranchuk instability of a topological crystal

TL;DR

This paper reports the first observation of Pomeranchuk instability in the topological surface state of arsenic, where the Fermi surface deforms into an elliptical shape, indicating nematic order in a topological metal.

Contribution

It demonstrates the occurrence of Pomeranchuk instability in a topological surface state, a novel setting not requiring van-Hove singularities or multi-orbital effects.

Findings

Fermi surface deformation into an elliptical shape at nematic state energies

Direct visualization of nematic order via scanning tunneling spectroscopy

First realization of Pomeranchuk instability in a topological surface state

Abstract

Nematic quantum fluids appear in strongly interacting systems and break the rotational symmetry of the crystallographic lattice. In metals, this is connected to a well-known instability of the Fermi liquid-the Pomeranchuk instability. Using scanning tunneling microscopy, we identified this instability in a highly unusual setting: on the surface of an elemental topological metal, arsenic. By directly visualizing the Fermi surface of the surface state via scanning tunneling spectroscopy and photoemission spectroscopy, we find that the Fermi surface gets deformed and becomes elliptical at the energies where the nematic state is present. Known instances of nematic instability typically need van-Hove singularities or multi-orbital physics as drivers. In contrast, the surface states of arsenic are essentially indistinguishable from well-confined isotropic Rashba bands near the Fermi level, rendering our finding the first realization of Pomeranchuk instability of the topological surface state.