Highly Frustrated Interactions in Magnetic and Other Condensed Matter Systems

点击翻译按钮获取中文摘要

This is a research proposal to theoretically study condensed matter systems, in particular magnetic ones, where the relevant microscopic degrees of freedom are subject to strongly competing (frustrated) interactions. Four broad problematics of experimental pertinence where novel phenomena arising from high frustration will be investigated.******In most disorder-free condensed matter systems, including highly frustrated ones, the low-temperature state displays homogeneous dynamics of the constitutive atoms, molecules or magnetic moments (spins) above a nanometer length scale. Glasses, which exhibit heterogeneous dynamics (HD), are a notable exception. In a recent study, we discovered a rare disorder-free three-dimensional spin model that displays a state with frozen and dynamic regions, thus HD, and coined the name spin slush for that state. We will uncover the general rules governing the formation of a spin slush in a magnetic system, focusing first on the possible manifestation of a spin slush state in two-dimensional models and study their spatial and dynamical properties along with the role of quantum effects.******Highly frustrated magnetic systems are often described by gauge theories reminiscent of the theory of electromagnetism for which it is well understood that boundary conditions on the components of the electric and magnetic fields play a fundamental role. Motivated by this observation, we will investigate how boundary conditions affect the properties of highly frustrated magnetic materials in nanometer size thin films such as those under current experimental investigation. Most importantly, we will determine what are the boundary conditions acting on the gauge fields that describe classical and quantum spin ice thin films. ******Small polar molecules such as H2O and HF can be encapsulated inside C60 buckyballs which form a regular crystal structure. There is current interest in understanding both the spectroscopy of such nanoconfined systems as well as the collective (ferroelectric) behaviour they may exhibit. By combining exact diagonalization, density functional theory and various many-body methods, we will investigate the putative development of such collective behaviour in these quantum systems.******In most magnetic systems, the spins interact via a so-called bilinear spin-spin exchange and most theoretical studies of highly frustrated magnetic systems consider such a setting. There are, however, real materials with puzzling properties where significant non-bilinear interactions are expected to exist. We will use a combination of analytical and numerical methods to explore whether such interactions can indeed explain the experimental behaviours of those systems.******Results from this research will significantly contribute to our global understanding of highly frustrated condensed matter systems and may lead to exciting discoveries.**