Pressure-induced Lifshitz transition in NbP: Raman, x-ray diffraction, electrical transport and density functional theory

TL;DR

This study combines experimental and theoretical methods to reveal a pressure-induced Lifshitz transition in NbP, characterized by changes in Raman modes, resistivity, and electronic structure, while TaP remains stable under pressure.

Contribution

It provides the first combined experimental and DFT evidence of a Lifshitz transition in NbP under pressure, highlighting the contrasting behavior of TaP.

Findings

NbP shows a Lifshitz transition at ~9 GPa.

Raman modes of NbP harden with pressure and slope change at P_c.

TaP remains stable without phase transition under pressure.

Abstract

We report high pressure Raman, synchrotron x-ray diffraction and electrical transport studies on Weyl semimetals NbP and TaP along with first-principles density functional theoretical (DFT) analysis. The frequencies of first-order Raman modes of NbP harden with increasing pressure and exhibit a slope change at P$_c$ $\sim$ 9 GPa, and its resistivity exhibits a minimum at P$_c$. The pressure-dependent volume of NbP exhibits a change in its bulk modulus from 207 GPa to 243 GPa at P$_c$. Using DFT calculations, we show that these anomalies are associated with pressure induced Lifshitz transition which involves appearance of electron and hole pockets in its electronic structure. In contrast, results of Raman and synchrotron x-ray diffraction experiments on TaP and DFT calculations show that TaP is quite robust under pressure and does not undergo any phase transition.