Emergent Dirac carriers across a pressure-induced Lifshitz transition in black phosphorus

TL;DR

This study identifies optical signatures of a pressure-induced Lifshitz transition in black phosphorus, revealing the emergence of Dirac fermions and changes in Fermi surface topology through pressure-dependent optical measurements.

Contribution

It demonstrates the first optical detection of a Lifshitz transition in a clean elemental system, linking Fermi surface topology changes to observable optical properties.

Findings

Observation of a change in Drude plasma frequency above 1.5 GPa

Detection of massless Dirac fermions emerging at the transition

Identification of structural phase transitions at higher pressures

Abstract

The phase diagrams of correlated systems like cuprates or pnictides high-temperature superconductors are characterized by a topological change of the Fermi surface under continuous variation of an external parameter, the so-called Lifshitz transition. However, the large number of low-temperature instabilities and the interplay of multiple energy scales complicate the study of this phenomenon. Here we first identify the optical signatures of a pressure-induced Lifshitz transition in a clean elemental system, black phosphorus. By applying external pressures above 1.5 GPa, we observe a change in the pressure dependence of the Drude plasma frequency due to the appearance of massless Dirac fermions. At higher pressures, optical signatures of two structural phase transitions are also identified. Our findings suggest that a key fingerprint of the Lifshitz transition in solid state systems, and in absence of structural phase transitions, is a discontinuity of the Drude plasma frequency due to the change of Fermi surface topology.