Liquid Crystal Order in Condensed Matter Systems

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

Liquid-crystals, defined as states of condensed matter intermediate in their properties between fully disordered isotropic liquids and fully ordered crystals are ubiquitous in nature. The principal investigator (PI) will study a variety of realizations of liquid crystal phases and transitions between them in novel contexts, with a unifying thread being importance of thermal and/or quantum fluctuations and static heterogeneities that lead to universal phase behavior. One class of such problems that will be studied, building on the PI's earlier work on smectic-A and discotics, is effects of quenched disorder on various types of liquid crystal orders, such as cholesteric, smectic-C, antiferroelectric and others, as realized by liquid crystals confined inside a random matrix of a rigid aerogel and/or a flexible aerosil. A dynamic theory of these systems will also be developed. Another focus will be the study of polymer-liquid crystal composite materials that hold considerable technological promise by combining mechanical properties of plastics and rubber with electro-optic properties of conventional fragile liquid crystals. Such materials, as for example realized by liquid-crystal elastomers and gels, also pose many fundamental theoretical questions, not unrelated to the aforementioned problem of liquid crystals in a random matrix, e.g., aerogel, with the randomly crosslinked polymer matrix playing the role of quenched disorder. Recently discovered microscopically achiral bent-core (banana-shaped) liquid crystals are exciting because they exhibit a spontaneous breaking of chiral symmetry and an accompanying spontaneous ferroelectricity. The PI will work to map out their rich phase diagram, explore phases, and elucidate the nature of this chiral symmetry breaking both in the orientationally ordered liquid and spatially ordered smectic phases. There are a number of recently discovered "hard" condensed matter systems that also appear to exhibit liquid crystal order. A previously studied example is a spontaneous vortex solid in putative ferromagnetic superconductors at zero field, that therefore have a symmetry of a columnar liquid crystal phase. Another example that will be studied is the putative "smectic vortex glass" state realizable in type-II superconductors with vortices running perpendicular to a random array of parallel columnar defects. The PI will explore thermal fluctuations, pinning and dissipation (I-V) of such systems with the goal of explaining recent puzzling experiments in such geometry. Possible electronic liquid crystal states in the quantum Hall regime of partially filled high Landau levels is another exciting direction of research. The PI will elucidate the phenomenology of quantum Hall nematic, aiming to develop and bridge its description from two complementary points of view: from the ordered side as a quantum-melted smectic and from the disordered side as an orientationally-ordered Fermi-liquid of composite fermions. A description of a quantum Hall smectic from the point of view of a translationally-ordered composite Fermi-liquid will also be studied and related to the previously developed Hartree-Fock smectic state. The research affects fundamental issues to applied technology. The PI is active in educational activities including K-12 and public outreach. %%% Liquid-crystals, defined as states of condensed matter intermediate in their properties between fully disordered isotropic liquids and fully ordered crystals are ubiquitous in nature. The principal investigator (PI) will study a variety of realizations of liquid crystal phases and transitions between them in novel contexts, with a unifying thread being importance of thermal and/or quantum fluctuations and static heterogeneities that lead to universal phase behavior. The research affects fundamental issues to applied technology. The PI is active in educational activities including K-12 and public outreach. ***