Electron correlation and disorder in Hg_(1-x)Cd_xTe in a magnetic field

Abstract

We report both linear and nonlinear magnetoconductance measurements on two different density samples of similar stoichiometry Hg_(1-x)Cd_xTe for 0.01<T<2.5 K and 0<H<80 kOe. The critical magnetic field for driving the samples through the metal-insulator transition is proportional to temperature at low T and saturates at T∼2 K, in quantitative agreement with a theory for the melting of a Wigner crystal in magnetic field. In the insulating state, we observe a non-Ohmic I-V characteristic at threshold electric fields less than 1 mV/cm. By analogy to theories for charge-density-wave depinning, we estimate that the electrons are correlated over regions of a few hundred lattice spacings. Finally, we map out the phase boundary between the low-T–high-H electron solid and the high-T–low-H correlated fluid, explicitly demonstrating the necessity of millikelvin temperatures for studying the relative roles of disorder and Coulomb interactions in the electron solid.