In-situ control of topological phase transitions in Cd₃As₂ detected via the circular photogalvanic effect

Topological devices have garnered intense interest over the previous decades, attributed to their suppressed backscattering, versatile spin texture, strong spin-orbit coupling, chemical robustness, and symmetry protected states. Dirac semimetal Cd₃As₂ is a member of the topological semimetal family and possesses these characteristics on top of an attractively long spin diffusion length. Topological phase transitions can be achieved reversibly through control over breaking certain symmetries, including crystal inversion and time reversal.

Spin injection via circularly polarized light is a nonintrusive and efficient method of utilizing spin properties in quantum device and spintronics applications and can be accomplished by an assortment of mechanisms, including the circular photogalvanic effect (CPGE). CPGE induced helicity dependent photocurrent modulation requires broken inversion symmetry, and thus can be used to probe topological phase transitions as the modulation is switched on and off. Recently, a local transition from Dirac semimetal to topological insulator was reported in Cd₃As₂ near the vicinity of the metal-semimetal interface, where a strong in-plane Schottky field locally breaks inversion symmetry. Using scanning photocurrent microscopy, we further explore means of controlling phase transitions in-situ via liquid ion top gating, strain, and doping.