Infrared Conductivity of Elemental Bismuth under Pressure: Evidence for an Avoided Lifshitz-Type Semimetal-Semiconductor Transition

TL;DR

This study investigates how pressure affects the infrared conductivity of elemental bismuth, revealing interaction effects that challenge the traditional Lifshitz transition model and suggesting a more complex transition mechanism.

Contribution

The paper provides experimental evidence of interaction effects in bismuth's pressure-induced transition, highlighting the importance of electron interactions beyond pure band theory.

Findings

Signatures of strongly coupled charge-plasmon features

Plasma frequency remains finite up to transition

Evidence of interaction effects contradicting pure Lifshitz transition

Abstract

The application of pressure to elemental bismuth reduces its conduction-valence band overlap, and results in a semimetal-semiconductor (SMSC) transition around 25 kbar. This transition is nominally of the topological "Lifshitz" Fermi surface variety, but there are open questions about the role of interactions at low charge densities. Using a novel pressure cell with optical access, we have performed an extensive study of bismuth's infrared conductivity under pressure. In contrast to the expected pure band behavior we find signatures of enhanced interaction effects, including strongly coupled charge-plasmon (plasmaron) features and a plasma frequency that remains finite up to the transition. These effect are inconsistent with a pure Lifshitz bandlike transition. We postulate that interactions play a central role in driving the transition.