Chiral Floquet Engineering on Topological Fermions in Chiral Crystals

TL;DR

This paper demonstrates how circularly polarized light can manipulate topological fermions in chiral crystals, inducing momentum shifts and transient Hall effects without destroying their gapless nature, opening avenues for optoelectronic applications.

Contribution

It introduces the concept of Floquet chirality index to describe chirality-dependent light-matter interactions in topological fermions within chiral crystals.

Findings

Light pumping displaces topological fermion crossing points in momentum space.

CPL induces transient anomalous Hall signals in non-magnetic CoSi.

Floquet chirality index governs the amplitude and direction of momentum shifts.

Abstract

The interplay of chiralities in light and quantum matter provides an opportunity to design and manipulate chirality-dependent properties in quantum materials. Herein we report the chirality-dependent Floquet engineering on topological fermions with the high Chern number in chiral crystal CoSi via circularly polarized light (CPL) pumping. Intense light pumping does not compromise the gapless nature of topological fermions in CoSi, but displaces the crossing points in momentum space along the direction of light propagation. The Floquet chirality index is proposed to signify the interplay between the chiralities of topological fermion, crystal, and incident light, which determines the amplitudes and directions of light-induced momentum shifts. Regarding the time-reversal symmetry breaking induced by the CPL pumping, momentum shifts of topological fermions result in the birth of transient anomalous Hall signals in non-magnetic CoSi within an ultrafast time scale, which Mid-infrared (IR) pumping and terahertz (THz) Kerr or Faraday probe spectroscopy could experimentally detect. Our findings provide insights into exploring novel applications in optoelectronic devices by leveraging the degree of freedom of chirality in the non-equilibrium regime.