Disorder and Dynamics in Solids and Superfluids

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

TECHNICAL SUMMARY This award supports theoretical research and education on nonequilibrium statistical physics spanning from classical to quantum systems. The research will focus on three areas: the structure and dynamics of random solids, non-equilibrium states and avalanching in superfluid helium flowing through nanopore arrays, and the structure and dynamics of ordering in laser-driven atomic systems housed in photonic cavities. Random solids are materials created via the permanent chemical bonding of randomly selected constituents, and are well exemplified by vulcanized rubber. This bonding creates a new state of matter, which acquires a nonzero shear modulus and spatial localization of its constituents - but with no long-range crystallinity. The PI's past work of has led to a fairly refined understanding of the static equilibrium structure and elasticity of simple random solids. The PI will develop an understanding of dynamics in simple random solids and their parent liquids, and when the materials exhibit long- or short-range liquid crystallinity, how this ordering interacts with the structure of the random solid. To accomplish these goals powerful statistical-mechanical tools will be applied that properly and instructively account for the deeply random chemical-level architecture that such materials possess. Motivated by beautiful experiments due to the Berkeley group, the PI plans to address the nature of helium superflow through arrays of thousands of nanoscale ?Josephson pores? connecting two reservoirs. The PI?s recent work argues that the qualitative nature of the flow depends crucially on a ?hidden? competition between superfluid "elasticity" and disorder, which arises from pore-to-pore variability. This work suggests that collective system-spanning "ruptures" in the superflow can occur at weak, but not at strong, disorder, these regimes being separated by a non-equilibrium phase transition that has antecedents in several condensed-matter and geophysical settings. The PI plans to construct a detailed theory of helium superflow through nanopore arrays that incorporates the effects of fluctuations and experiment geometry, and builds a statistical characterization of the flow dynamics. Laser-driven atomic gases, trapped in high-finesse optical cavities are expected to undergo fascinating nonequilibrium quantum phase transitions to states of strong, spontaneous organization among the atoms, which self-consistently populate either the even or the odd anti-nodes of certain modes of the cavity radiation. For suitably designed cavities, these transitions are expected to be accompanied by strong fluctuations in the atomic organization, which will imprint themselves on the spatial and temporal correlations of the light leaking from the cavity. The PI aims to apply a wide array of condensed matter techniques in developing a thorough picture of the ordering, its steady-state fluctuations, and the rich kinetics via which this nonequilibrium steady state is achieved. NONTECHNICAL SUMMARY This award supports a theoretical research and education program across hard and soft condensed matter physics with the study of systems and materials that are out of equilibrium and in which randomness plays an important role. The PI will conduct research in three areas. In the first the PI will study the properties of random solids ? materials made of a network of long chain-like molecules in which the chains are linked to each other at random places. In the second area the PI will study the flow of superfluid helium, a liquid at low temperature with remarkable properties such as the ability to flow without dissipation, through an array of nanoscale pores. In the third area the PI will study the nonequilbrium phases of atomic gases in an optical cavity and transitions among them that arise when a laser is applied. These three areas of research advance the field of statistical physics which seeks to discover universal principles that characterize systems that are far from equilibrium and link seemingly unrelated systems. From a physical point of view, living things provide perhaps the most familiar example of systems that are far from equilibrium. This is fundamental research that will advance our understanding of systems and materials that are far from equilibrium.