# Pressure induced evolution of band structure in black phosphorus studied by $^{31}$P-NMR

## TL;DR

This study uses $^{31}$P-NMR and band calculations to investigate how pressure affects the electronic band structure of black phosphorus, revealing gap closure and increased conductivity at high pressure.

## Contribution

It provides a combined experimental and theoretical analysis of pressure-induced band structure evolution in black phosphorus, confirming band calculations with NMR data.

## Key findings

- Pressure causes the semiconducting gap in black phosphorus to close.
- An abrupt increase in $1/T_1$ at 1.63 GPa indicates gap closure.
- The band calculations reliably predict the pressure dependence of the density of states.

## Abstract

Two-dimensional layered semiconductor black phosphorus (BP), a promising pressure induced Dirac system as predicted by band structure calculations, has been studied by $^{31}$P-nuclear magnetic resonance. Band calculations have been also carried out to estimate the density of states $D(E)$. The temperature and pressure dependences of nuclear spin lattice relaxation rate $1/T_1$ in the semiconducting phase are well reproduced using the derived $D(E)$, and the resultant pressure dependence of semiconducting gap is in good accordance with previous reports, giving a good confirmation that the band calculation on BP is fairly reliable. The present analysis of $1/T_1$ data with the complemental theoretical calculations allows us to extract essential information, such as the pressure dependences of $D(E)$ and chemical potential, as well as to decompose observed $1/T_1$ into intrinsic and extrinsic contributions. An abrupt increase in $1/T_1$ at 1.63GPa indicates that the semiconducting gap closes, resulting in an enhancement of conductivity.