Spin-orbit interaction driven collective electron-hole excitations in a noncentrosymmetric nodal loop Weyl semimetal

TL;DR

This study investigates how spin-orbit coupling and lack of inversion symmetry in NbP lead to unique Fermi surface structures and low-energy plasmon excitations, enhancing understanding of noncentrosymmetric nodal loop Weyl semimetals.

Contribution

It provides detailed first-principles analysis of the effects of SOC and inversion symmetry breaking on electronic structure and collective excitations in NbP, a nodal loop Weyl semimetal.

Findings

SOC causes splitting of degeneracies and complex Fermi surfaces.

Transport properties around 100 K are accurately reproduced with SOC included.

Low-energy plasmons in the 20-60 meV range are identified as a consequence of nodal loop splitting.

Abstract

NbP is one member of a new class of nodal loop semimetals characterized by the cooperative effects of spin-orbit coupling (SOC) and a lack of inversion center. Here transport and spectroscopic properties of NbP are evaluated using density functional theory methods. SOC together with the lack of inversion symmetry splits degeneracies, giving rise to "Russian doll nested" Fermi surfaces containing 4*10$^{-4}$ electron (hole) carriers/f.u. Due to the modest SOC strength in Nb, the Fermi surfaces map out the Weyl nodal loops. Calculated structure around T$^*$~100 K in transport properties reproduces well the observed transport behavior only when SOC is included, attesting to the precision of the (delicate) calculations and the stoichiometry of the samples. Low energy collective electron-hole excitations (plasmons) in the 20-60 meV range result from the nodal loop splitting.