Infrared study of ellipsoidal nodal ring semimetal SrAs₃

Dirac/Weyl semimetals, a novel class of quantum materials, are characterized by linearly dispersing energy bands from nodal point that obey relativistic Hamiltonians. For nodal point and nodal line Dirac/Weyl semimetals, optical studies showed unique features such as constant/linear optical conductivity σ₁^IB(ω) ∝ ω^(d_eff-2)/z (d_eff = effective lattice dimension and z = energy dispersion dimension) . Here we measured polarization-dependent optical reflectivity on SrAs₃ single crystals, a nodal-ring semimetal where E_f crosses only non-trivial band without interruption from trivial bands. For E//x, a flat optical absorption occurs up to 130meV, whereas drastically different behavior is observed for E//z. A SOC gap transition appears at 35meV for both polarizations. We perform theoretical calculations of σ₁^IB(ω) based on low-energy model Hamiltonian and DFT band calculations, and compare them with experimental σ₁^IB(ω). The Fermi surface structure (nodal ring vs nodal ellipsoid) and band dispersion (linear vs quadratic) of SrAs₃ are unveiled from this comparative study.