Terahertz nonlinear optics of chiral semimetals RhSn, HfSn, and PdGa

Topological semimetals have linear band dispersion around the band crossing which is near the Fermi level. Chiral topological semimetals have no spatial inversion symmetry, and they have non-vanishing second-order optical response. The band structure and nonlinear optical conductivity (NOC) $${\sigma }_{zxy}^{(2)}(0;\omega ,-\omega )$$ σ zxy ( 2 ) ( 0 ; ω , - ω ) of the isostructural chiral semimetals RhSn, HfSn, and PdGa are studied by the first-principles calculation in this work. Our calculation demonstrates that the maximal NOC $${\sigma }_{zxy}^{(2)}(0;\omega ,-\omega )$$ σ zxy ( 2 ) ( 0 ; ω , - ω ) of chiral semimetals RhSn is about $$\sim 1370\, \upmu \hbox {A/V}^{2}$$ ∼ 1370 μ A/V 2 under terahertz optical field with photon energy of $$\sim $$ ∼ 12 meV, while the maximal NOCs $${\sigma }_{zxy}^{(2)}(0;\omega ,-\omega )$$ σ zxy ( 2 ) ( 0 ; ω , - ω ) of HfSn and PdGa are $$600 \, \upmu \hbox {A/V}^{2}$$ 600 μ A/V 2 and $$240\, \upmu \hbox {A/V}^{2}$$ 240 μ A/V 2 , respectively. The relatively large NOC of RhSn can be interpreted by its multiple band crossing on the Fermi level, while multiple band crossings in the band structures of HfSn and PdGa are not on the Fermi level. Our calculations also reveal that the calculated imaginary part of dielectric function decreases with increasing photon energy, while the absorption coefficient increases with increasing photon energy in the terahertz region. The relatively large NOC makes chiral topological semimetal RhSn suitable for terahertz detection. Graphic Abstract