Temperature dependance of the photogalvanic effect in Bi2Se3 at milli-Kelvin Temperatures

The photogalvanic effect can probe the surface states of topological insulators. At optical photon energies surface states near the Dirac point are excited into bulk bands, whereas at energies commensurate with THz excitation, surface states are excited within the Dirac cone leading to a potential enhancement in sensitivity to topological surface states (TSS) and Berry phase. Here, we demonstrate measurements of the circular photogalvanic effect (CPGE) in the topological insulator Bi2Se3 with both optical and THz frequencies at room temperature. Furthermore, we also probe this effect at millikelvin temperatures with THz light. We find the CPGE increases rapidly below 2 K, and is potentially correlated with the weak antilocalization, which itself is dependent on phase coherence lengths. This work lays the foundation for studying both TI and TSS using CPGE at ultra-low temperatures.