Electronic correlations effect on nontrivial topological fermions in CoSi

TL;DR

This study investigates how electronic correlations influence the properties of exotic fermions in CoSi using advanced DFT+DMFT methods, revealing effects on quasiparticle lifetimes, effective masses, and surface states at 100 K.

Contribution

It provides the first detailed analysis of electronic correlation effects on nontrivial topological fermions in CoSi, including quasiparticle lifetimes and surface spectral functions.

Findings

Presence of both coherent and incoherent spectral features in bulk and surface states.

Quasiparticle lifetimes vary from 10^{-12} s to 10^{-8} s depending on conditions.

Effective masses of fermions are approximately 1.6 times the electron mass.

Abstract

The present study has been carried out to understand the effect of electronic correlations on the recently found fermions in CoSi. For which the spectral functions of bulk and (001) surface of CoSi have been investigated by using DFT+DMFT advanced methodology at T = 100 K with and without inclusion of spin-orbit coupling (SOC). All the newly found fermions are observed at $\Gamma$ and $R$ points similar to other theoretical and experimental reports. Our DFT+DMFT calculations for the bulk states have shown one extra hole pocket at $M$ point. Both coherent and incoherent features have been observed in the spectra of bulk CoSi. This indicates the presence of quasiparticle-quasiparticle (QP-QP) interactions which is eventually affecting the lifetime ($\tau$) of exotic fermionic QPs. For instance, the calculated $\tau$ for QPs at $\omega \sim $ -30 and -186 mev are found to be $\sim 10^{-9}$ s and $\sim 10^{-12}$ s, respectively when SOC is not considered. However, $G_0W_0$ corrections have shown $\tau$ for spin-1 fermionic QP at $\Gamma$ to be infinite while for double Weyl fermionic QP at $R$ point to be $\sim 10^{-12}$ s. Their effective masses ($m^*$) have also been calculated as $\sim$ 1.60 and 1.64 at $\Gamma$ and $R$ points, respectively. Furthermore, the spectral functions at T = 100 K of (001) surface have also shown both coherent and incoherent features. Consequently, at $\omega$ = 0 for surface states $\tau$ has been calculated of the order $\sim 10^{-8}$s for both without SOC and with SOC inclusions.