Current-Driven to Thermally Driven Multistep Phase Transition of Charge Density Wave Order in 1T-TaS.

Two-dimensional 1T-TaS is renowned for its exotic physical properties including superconductivity, Mott physics, flat-band electronics, and charge density wave (CDW) orders. In particular, the CDW phase transitions (PTs) in 1T-TaS attracted extensive research interest, showing prominent potential in electronic devices. However, mechanisms underlying electrically driven PTs remain elusive. Here, we systematically studied the evolution of multistep PTs during the - sweep in 1T-TaS. Comprehensive investigations, covering variations in temperature, pulsed voltage duration, and light illumination, reveal that the underlying PT mechanism shifts from current-driven to thermally driven with increasing current. Initially, the current-driven PT step occurs at a constant current density, independent of the temperature. Subsequently, thermally driven PT steps manifest at a constant conductivity highly sensitive to the thermal effect. These transitions are strongly associated with the metastable CDW electronic structures and their response to carrier injection and thermal variations. Our findings reconcile long-standing debates regarding the electrically driven CDW PTs in 1T-TaS.