  We demonstrate a new type of dual gate transistor to induce record electric
fields through two-dimensional materials (2DMs). At the heart of this device is
a 2DM suspended between two volumes of ionic liquid (IL) with independently
controlled potentials. The potential difference between the ILs falls across an
ultrathin layer consisting of the 2DM and the electrical double layers above
and below it, thereby producing an intense electric field across the 2DM. We
determine the field strength via i) electrical transport measurements and ii)
direct measurements of electrochemical potentials of the ILs using
semiconducting 2DM, WSe2. The field strength across the material reaches more
than 3.5 V/nm, the largest static electric field through any electronic device
to date. We demonstrate that this field is strong enough to close the bandgap
of trilayer WSe2 driving a semiconductor-to-metal transition. Our approach
grants access to previously-inaccessible phenomena occurring in ultrastrong
electric fields.

Applied Physics;Mesoscale and Nanoscale Physics