Symmetry change of quantum electron solids in double layer MoS2

Abstract

Electrons in transition metal dichalcogenides stacked on opposite sides of BN of thickness d can form solids, which have no long range position order but are characterized by a finite shear modulus. The melting temperature Tm is characterized by the occurrence of unbound quantum topological defects. Tm of this solid is four orders of magnitude larger than that of previously studied electron solids in Si-MOSFETs. As the density n = n0 × 1012/cm2 is changed so that both the top and the bottom electron densities are the same, for n0 > 1.5 with d = 5 nm, a hexagonal solid is manifested experimentally by a five order of magnitude increase in Coulomb drag resistance Rdrag at room temperature. This resistance change corresponds to a four orders of magnitude better subthreshold slope, the key parameter for semiconductor device low power switching, over existing limits for MOSFETs from “Boltzmann’s tyranny.” The symmetry of the two-layer solid can be tuned by varying the density. The hexagonal lattice becomes soft at n0 ≈ 1.5. There is a further two orders of magnitude increase in Rdrag due to an increase in disorder caused by the large quantum fluctuation of the lattice position that is of 0.4 order of the lattice spacing. The subthreshold slope is improved by two more orders of magnitude. For n0 < 1.5, different phases of the solid corresponding to peaks of Rdrag of different magnitude at different gate voltages start to form. This raises the intriguing possibility of making new classes of devices with ternary and higher order systems where the different phases correspond to different logical states and not just two states of on (low resistance) and off (high resistance).