Zero and Finite Temperature Critical Phenomena in Quantum Systems

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This project explores the properties of matter at low temperatures. Advantage is taken of the well-established properties of He-4 at low temperatures to illuminate a number of problems in condensed maatter physics. One sub-project addresses the influence of controlled defects on the critical phenomena of a pure system. The introduction of a low density structural impurity into liquid helium can produce a striking alteration in the critical pehnomena. An understanding of this problem will enhance our understanding of the role of defects for a wider range of phase transitions. A second area is the study of boson localization in He-4 films adsorbed on a heterogeneous substrate. The study of the physics of a boson system, such a a helium film in the random potential of aheterogeneous substrate, offers an interesting complement to studies of the metal-insulator transition and the superconductor- insulator transition in dirty superconductors. A third topic will be the study of a dissipative flow of superfluid helium through a porous medium. This is a boson analog to the technologically important problem of the vortex liquid and flux-flow regimes of high Tc superconductors. %%% This project explores the properties of matter at very low temperatures--below minus 450 degrees Fahrenheit. The project deals with a superfluid, helium, which exhibits behavior which, by analogy, can be related to phenomena in other materials, particularly high Tc superconductors. In addition, the research deals with phase transitions and provides fundamental information bearing on solid-liquid melting (and other transformations) that occurs in all materials.