Electric Field Effect of T_C in Thin Flakes of the Excitonic Insulator Ta₂NiSe₅

The layered, small-gap semiconductor Ta₂NiSe₅ is a prominent excitonic insulator candidate with a T_C of 326 K. We investigated the electric field effect of the excitonic insulator transition temperature in a device fabricated with thin (15 nm) Ta₂NiSe₅. Flakes of Ta₂NiSe₅ were obtained by mechanical exfoliation and transferred onto narrow bottom gates insulated with Al₂O₃, and the Ta₂NiSe₅ was then contacted with Cr/Au. Measurements of source-drain current as a function of temperature revealed a small yet sharp drop in current near T_C. A modest, reproducible shift of T_C by approximately 1 K was observed under a transverse electric field of +/- 0.5 V/nm. Future experiments with this and similar devices will probe the origin of this field effect on T_C, as well as the unexpected sign of the change in current at T_C.