Electric Field Induced Mott Insulator to Soft-Gap Transition in α-RuCl₃

The Mott insulator to metal transitions have been an area of intense study in highly correlated systems for many years. Lately there has been interest transitions to other electronic phases. Here, we report new experiments that induce a transition by utilizing the high electric fields under a scanning tunneling microscope (STM) tip. We are able to reversibly control the apparent Mott gap size of α-RuCl₃ in STM experiments. At high fields, we can induce a collapse of the Mott gap into a soft “power law gap” phase. We directly quantify the power law exponent characterizing the gap shape which varies from ~ 2 in the Mott Insulator phase at low fields down to less than 1 at very strong fields. These observations will be discussed in the context of the generic soft gap phenomenology in correlated materials.