  Dynamic control of conductivity and optical properties via atomic structure
changes is of tremendous technological importance in information storage.
Energy consumption considerations provide a driving force toward employing thin
materials in devices. Monolayer transition metal dichalcogenides are nearly
atomically-thin materials that can exist in multiple crystal structures, each
with distinct electrical properties. Using density functional approaches, we
discover that electrostatic gating device configurations have the potential to
drive structural semiconductor-to-semimetal phase transitions in some monolayer
transition metal dichalcogenides. For the first time, we show that the
dynamical control of this phase transition can be achieved in carefully
designed electronic devices. We discover that the semiconductor-to-semimetal
phase transition in monolayer MoTe2 can be driven by a gate voltage of several
Volts with appropriate choice of dielectric. Structural transitions in
monolayer TaSe2 are predicted to occur under similar conditions. While the
required field magnitudes are large for these two materials, we find that the
gate voltage for the transition can be reduced arbitrarily by alloying, e.g.
for MoxW1-xTe2 monolayers. We have developed a method for computing phase
diagrams of monolayer materials with respect to charge and voltage, validated
by comparing to direct calculations and experimental measurements. Our findings
identify a new physical mechanism, not existing in bulk materials, to
dynamically control structural phase transitions in two-dimensional materials,
enabling potential applications in phase-change electronic devices.
