Renormalization-group study of superfluidity and phase separation of helium mixtures immersed in a nonrandom aerogel

Superfluidity and phase separation in 3He-4He mixtures immersed in a jungle-gym (nonrandom) aerogel are studied by renormalization-group theory. Phase diagrams are calculated for a variety of aerogel concentrations. Superfluidity at very low 4He concentrations and a depressed tricritical temperature are found at the onset of superfluidity. A superfluid-superfluid phase separation, terminating at an isolated critical point, is found entirely within the superfluid phase. These phenomena and trends with respect to aerogel concentration are explained by the connectivity and tenuousness of a jungle-gym aerogel. copyright 1997 The American Physical Society