Ab initio study of quantized circular photogalvanic effect in chiral multifold semimetals

Abstract

So far, the circular photogalvanic effect (CPGE) is the only possible quantized signal in Weyl semimetals. With inversion and mirror symmetries broken, Weyl and multifold fermions in band structures with opposite chiralities can stay at different energies and generate a net topological charge. Such a kind of net topological charge can present as a quantized signal in the circular polarized light-induced injection current. According to current theoretical understanding, RhSi and its counterparts are believed to be the most promising candidates for the experimental observation of the quantized CPGE. However, a real quantized signal has yet to be experimentally observed. Since previous theoretical studies for the quantized CPGE were based on an effective model but not realistic band structures, it should lose some crucial details that influence the quantized signal. The current status motivates us to perform a realistic ab initio study for the CPGE. Our result shows that RhSi and PtAl in chiral multifold semimetals are alternative materials for obtaining the quantized CPGE which is very easy to be interfered with by trivial band-related optic transitions, and a fine tuning of the chemical potential by doping is essential for the observation of the quantized CPGE. We perform an ab initio analysis for the quantized CPGE based on a realistic electronic band structure and provide an effective way to solve the current problem for the given materials.

Optical Response of Chiral Multifold Semimetal PdGa

“…The lack of inversion and mirror symmetries, in combination with SOC, leads to the splitting of bands around the high symmetry points Γ and R, giving rise to a non-collinear spin arrangement with Chern numbers χ = ±4 [29] with maximally extended surface states, ranging from the center to the edge of the Brillouin zone [25,27,30]. In such semimetals, the quantized circular photogalvanic effect has been predicted, which, by effect of topological states, constitutes a photocurrent, quantized in units of material-independent fundamental constants [31][32][33][34].…”

Optical response of the chiral topological semimetal RhSi

“…The firstprinciples calculations predicted relatively strong second order optical conductivity σ (2) xyz (0; ω, −ω) = σ xyz + η xyz in topological semimetals RhSn and RhSi in range of Terahertz [30,31]. By effective model Hamiltonian and the first-principles calculations, circular photogalvanic effect is predicted in chiral topological semimetal RhSi [32][33][34][35]. Experimentally, the circular photogalvanic effect in the chiral topological semimetal RhSi is observed in an energy window below 0.65 eV [36][37][38].…”

Electronic structure and unconventional non-linear response in double Weyl semimetal SrSi$_2$

“…We note that higher topological charge is also observed for multifold band crossing with integer spin in topological chiral crystals such as, the transition metal monosilicides MSi (M = Co, Mn, Fe, Rh) [26][27][28][29][30]. The Fermi arc surface states and chiral anomaly induced negative magnetoresistance directly reflect the topological nature of WSM through its transport signatures [31,32].…”