2D electrons floating on a suspended atomically thin dielectric

Abstract

The 2D electrons trapped in vacuum near the atomically thin dielectric (ATD, mono- or N-layer film of h-BN or transition metal dichalcogenide) are considered. ATD is suspended above the back gate and forms the capacitor, which is controlled by the biased voltage determining 2D concentration, n2D. It is found that the leakage current through ATD is negligible, and the effect of the polarizability of ATD is weak if N≤5. At temperatures T=0.1–15 K and n2D=5×108–1010cm−2, one deals with the Boltzmann liquid having a macroscopic thickness of ∼100 A. Due to the bending of ATD, the quadratic dispersion law of the flexural vibrations is transformed into the linear one at small wave vectors. The scattering processes of the electrons caused by these phonons or the monolayer islands on ATD are examined and the momentum and energy relaxation rates are analyzed based on the corresponding balance equations. The momentum relaxation times vary over orders of magnitude in the above region (T, n2D) and N. The response may change from the polaron transport, for a perfect single-layer ATD at low T and high n2D, to the high-mobility (≥107cm2/Vs) regime at high T and low n2D. The quasi-elastic energy relaxation due to phonon-induced scattering is considered, and the conditions for the heating of electrons by a weak in-plane electric field are found.