Properties of Electron-Hole-Drops in Ge in Magnetic Field

Abstract

In a number of semiconductors like Ge, Si, GaP and SiC^1–3 a first order electronic phase transition occurs below a critical temperature in a dense system (plasma) of electrons and holes or excitons. The plasma separates into a high density metallic electron-hole liquid (EHL) and a low density gas-like plasma. Macroscopically the EHL exhibits properties of a classical fluid existing in the form of drops, which can be driven by external forces. Microscopically the fluid has a strong quantum character (in Ge the de Boer number is ^~80). The results of most recent experiments on the EHL in Ge in magnetic fields up to 20T are discussed in this paper. Both macroscopic and microscopic properties of the liquid are revealed by these experiments. Magnetic field investigations of the EHL in Ge are particularly interesting since it is possible to observe at one and the same field effects characteristics of the low field regime, where the Fermi energy is larger than the splitting of the lowest Landau levels, and of the high field regime where the Fermi energy is smaller than the splitting of the Landau levels. The reason for this unusual behaviour is that the EHL is a two-component fluid with energy splittings of the lowest electron and hole magnetic subbands differing by more than one order of magnitude. In Ge for Hll <111> the high field limit is reached for electrons at ^~3T and for holes at ^~77T.