Nonlinear THz Spectroscopy of the Dirac Semimetal Cd₃As₂

Topological semimetals are materials with linear band touchings in their bulk band structure, resulting in low-energy excitation that behaves like a Weyl or Dirac fermion, resulting in novel electronic properties. Cd₃As₂, a Dirac topological semimetal, has become a promising candidate for integration into opto-electronic devices due to its chemical stability.  Here we investigate the linear and nonlinear THz response of (112) Cd3As2 thin films grown on (111) GaAs via molecular beam epitaxy (MBE).  We identify the large nonlinear response as stemming from pump-probe processes. We then use THz-pump, THz-probe to measure the temperature-dependent and fluence-dependent relaxation rates of the quasiparticle excitations in this material.