Nonlinear terahertz phononics in the Dirac semimetal Cd3As2

Abstract

The coherent lattice dynamics in the three-dimensional (3D) Dirac semimetal Cd3As2 is investigated in the nonperturbative regime of light-matter interaction using coherent two-dimensional terahertz (THz) spectroscopy, as a function of time delay and field strength. The phase-resolved nonlinear signal reveals a coherent phonon mode at 1.48 THz, corresponding to the B2g Raman-active mode, characterized by the periodic motion of two cadmium atoms in the substructure toward and away from two cadmium-vacant sites. The interaction of a strong THz electric field with the 3D Dirac semimetal Cd3As2 leads to transient charge carrier imbalance via tunneling ionization, which results in a displacive force that drives the lattice dynamics of a noninteracting Raman-active mode. The selective excitation of otherwise inaccessible phonon modes enables precise control over the material's properties at the atomic level, opening new pathways to manipulate its topological characteristics.