Suppression of second-harmonic generation from linear bands in the topological multifold semimetal RhSi

Abstract

Recent experiments in the topological Weyl semimetal TaAs have observed record-breaking second-harmonic generation, a non-linear optical response at 2ω generated by an incoming light source at ω. However, whether second-harmonic generation is enhanced in topological semimetals in general is a challenging open question because their band structure entangles the contributions arising from trivial bands and topological band crossings. In this work, we circumvent this problem by studying RhSi, a chiral topological semimetal with a simple band structure with topological multifold fermions close to the Fermi energy. We measure second-harmonic generation (SHG) in a wide frequency window, ω ∈ [0.27, 1.5] eV and, using first principle calculations, we establish that, due to their linear dispersion, the contribution of multifold fermions to SHG is subdominant as compared with other regions in the Brillouin zone. Our calculations suggest that parts of the bands where the dispersion is relatively flat contribute significantly to SHG. As a whole, our results suggest avenues to enhance SHG responses.

Linear and Nonlinear Optical Responses of Chiral Multifold Semimetals

“…5.4 we reproduce the experimental and DFT results originally reported in Ref. [76] for the second-harmonic susceptibility of RhSi in the energy range 0.27−1.5 eV. To understand the SHG features observed in the experiment we compare the results with a DFT calculation performed using the EXCITING package 156 .…”

“…We will discuss the results of the theoretical calculations in comparison with the experimental data, originally reported in Ref. [76].…”

“…The results are calculated for the pristine RhSi system (E f = 0) and originally presented in Ref. [76]. The figure shows that by adjusting ∆, the energy difference between bands ω mn is modified, and thus the optical transitions between bands.…”

“…This study was done in collaboration with Baozhu Lu, Kaustuv Manna, Claudia Felser, and Darius H. Torchinsky, who worked on the experiment, and Sharareh Sayyad, who performed the DFT calculations, and was originally presented in Ref. [76].…”

“…5.4 we reproduce the results for the SHG of RhSi using the DFT calculations. In order to compare the theoretical prediction with the experiment, the SHG response is calibrated with that of GaAs 142 in a similar fashion to the procedure followed in the experiment 76 .…”