Optical response of the chiral topological semimetal RhSi

Abstract

We studied the linear electro-optic effect of chiral topological semimetal RhSi which is characterized by high-fold chiral fermions separated in energy space. We identify that the general second order conductivity σ(2) xyz (ω = ω1 + ω2; ω1, ω2) includes a real symmetric component and an imaginary antisymmetric component, which are from the inter-band shift and intra-band injection current with frequency ω, respectively. The σxyz is significantly enhanced by the high electron velocity and nontrivial band topology of chiral fermion, and modifies the phase velocity of light wave. We also predict that the electro-optic coefficient χ(2) xyz (ω; ω, 0) of chiral crystal RhSi is about 7000 pm/V at photon energy 0.01 eV and 1.1 eV, which is about 200 times that of widely used LiNbO3 crystal. The giant electro-optic coefficient renders a relatively low half-wave voltage in order of hundreds volt, and demonstrates potential application as electro-optic crystals for the wavelength in the second telecom window of optical fiber communications.

Nodal Semimetals: A Survey on Optical Conductivity

“…[ 26–77 ] There are also theoretical studies, where is computed for particular semimetal compounds based on their band‐structures. [ 78–82 ] Some studies combine both, experiment and band‐structure‐based computations. [ 27,28,83,84,85 ] We would like to stress here that usually the match between measurements and such computations is only qualitative.…”

“…Herein, we review recent reports on the experimental determination of in RhSi [ 38,118 ] and compare the obtained results with the available theoretical calculations. [ 58,82 ] As noticed in Section 2, the optical conductivity of multifold semimetals is supposed to demonstrate a linear‐in‐frequency , similarly to 3D Dirac and Weyl semimetals.…”

“…The experimental data are from the study by Maulana et al [ 38 ] (black line) and from the study by Rees et al [ 118 ] (green line). The theoretical curve is adapted from the study by Li et al [ 82 ]…”

“…The mismatch can be related to deviations of the bands from linearity even at low energies. [ 82,111,112 ] This can be clarified in more advanced band‐structure‐based optical conductivity calculations. In any case, the predicted linear run of is experimentally confirmed for a multifold semimetal.…”

Optoelectronic Fingerprints of Interference between Different Charge Carriers in Graphene Superlattices and Analogies to Twisted Graphene Bilayers

“…Multifold fermions are the generalization of Weyl fermions to a higher effective spin representation that exhibit a remarkable optoelectronic response, including exotic circular photogalvanic effects [58][59][60][61][62]. A number of crystals have recently been shown to exhibit multiple species of these quasiparticles coexisting at low energies and, particularly, the study of their optical conductivity has been the focus of multiple theoretical and experimental works [58,61,[63][64][65][66][67][68][69]. It has been noted in previous works [39,41,51] that, due to the folding of the K and K valleys into the Γ-point, the resulting low-energy band structure in some Kekulé-modulated superlattices can be described by higher pseudospin representations of the Dirac equation [70].…”