Two-dimensional semimetal in HgTe-based quantum wells

The first results are reported from a study of a new two-dimensional electron system, a two-dimensional semimetal, that is observed in wide quantum wells based on mercury telluride, which have an inverted band spectrum. Magnetotransport experiments confirm the existence of a semimetal state in quantum wells with (013) and (112) orientations and thicknesses of 18-21 nm. These experiments show that the band overlap Delta = 3-5 meV. A comparison of the experimentally determined Delta with a theoretical calculation of the energy spectrum reveals the fundamental role of strain effects in the formation of the semimetal state. Scattering processes in the two-dimensional semimetal are studied and it is found that the jump in the electron mobility during electronic metal-two-dimensional semimetal transitions is caused by shielding of electron scattering on impurities by holes. The substantial, anomalous rise in the resistivity of the two-dimensional semimetal with increasing temperature is caused by electron-hole scattering. This is the first observation of the direct effect of interparticle scattering (Landau mechanism) on the resistivity of metals. The properties of two-dimensional semimetals in the quantum Hall effect regime are examined. Primary attention is devoted to the observed suppression of strong localization under the conditions of the quantum Hall effect. It is shown that in a strong magnetic field the two-component electron-hole plasma has fundamentally different topological properties from those of an ordinary single-component (electron or hole) plasma. It is proposed that these lead to the appearance of an infinite set of conducting current states and to the suppression of localization. (C) 2011 American Institute of Physics. [doi:10.1063/1.3573648]