Anderson localization in a two-dimensional electron–hole system

Anderson localization is discovered in a highly disordered two-dimensional electron–hole system in a HgTe quantum well. The behavior of this localization is fundamentally different from that observed in widely studied two-dimensional one-component electron and hole systems. It is found that such system exhibits two-stage localization: two-dimensional holes are localized first, as particles with the effective mass almost an order of magnitude larger than that of electrons. Then, electrons become localized. It is also found that the system under study does not exhibit any metal–insulator transition: even at the electrical conductivity $\sigma > e^2/h$, an insulator-like temperature dependence is observed. The results for the first time draw attention to the problem of the nature of Anderson localization in a two-dimensional electron–hole system.