Collective plasmonic modes in the chiral multifold fermionic material CoSi

TL;DR

This paper explores the unique plasmonic excitations in the topological semimetal CoSi, revealing two distinct long-lived plasmon modes with potential for advancing topological plasmonics.

Contribution

It identifies and characterizes two novel plasmon modes in CoSi, linking them to its multifold fermionic excitations and demonstrating their potential for topological plasmonics.

Findings

Two distinct plasmon modes at 0.1 eV and 1.1 eV in CoSi.

The 0.1 eV mode is highly dispersive and linked to intraband oscillations.

The 1.1 eV mode is dispersionless and involves interband correlations.

Abstract

Plasmonics in topological semimetals offers exciting opportunities for fundamental physics exploration as well as for technological applications. Here, we investigate plasmons in the exemplar chiral crystal CoSi, which hosts a variety of multifold fermionic excitations. We show that CoSi hosts two distinct plasmon modes in the infrared regime at 0.1 eV and 1.1 eV in the long-wavelength limit. The 0.1 eV plasmon is found to be highly dispersive, and originates from intraband collective oscillations associated with a double spin-1 excitation, while the 1.1 eV plasmon is dispersionless and it involves interband correlations. Both plasmon modes lie outside the particle-hole continuum and possess long lifetime. Our study indicates that the CoSi class of materials will provide an interesting materials platform for exploring fundamental and technological aspects of topological plasmonics.