Quantum Fluid Mixtures in Different Phases

Variational theory of quantum fluid mixtures is presented with the emphasis on the stability and phase transitions. We give results on two systems where new interesting phases are predicted. Dilute mixtures of ³He impurities in the liquid ⁴He in two dimensions form loosely bound pairs, dimers. The binding energy of the dimer ranges from milli- to micro-Kelvins with increasing ⁴He density. The dimerised mixture of ³He atoms is stable up to maximum solubility of ≈ 3%. Electrons and holes in semiconductors form a homogeneous mixture, electron-hole liquid. We predict that at low densities this system becomes unstable against clustering of charges and a liquid phase with a mixture of bound charged clusters could be formed.