Multiple mechanisms of the low temperature photoresponse in niobium diselenide

Abstract

Niobium diselenide (NbSe2) is a layered transition metal dichalcogenide with novel quantum phases at low temperatures (T) such as superconductivity and charge density wave order. While its electronic correlations and the interaction between electrons and other collective modes have been explored extensively, a detailed study of the transport behavior of photo-excited charge carriers still remains elusive. Here, we report a systematic investigation of the photoresponse generated in homogenous NbSe2 nano-flakes near the superconducting critical temperature (Tc). By combining scanning photocurrent microscopy and classic photoconductivity measurements, three distinctive mechanisms of the photoresponse are established, including the band bending at the NbSe2–metal junction, the perturbation of the superconducting state, and the photo-bolometric effect. Among them, the photo-induced phase transition from the superconducting to normal state results in an extremely large photocurrent, which is tunable by the bias voltage and is consistent with the observation via the electrical transport characterization. The photoresponsivity of our device reaches 42.3 A/W, and the response time is less than 2 μs at T = 3.8 K for an excitation in the visible wavelength, whose performance could be further improved by optimizing the device design and the experimental condition. Our result sheds light on ultrasensitive broadband photodetection with atomically thin NbSe2 and points to a potential means of probing the correlated electronic phases by exploring light–matter interactions.