Searching for spin liquids in pyrochlore magnets

Par Owen Benton, Riken, Tokyo, Japon

Mercredi 08 Mars, 14h, Salle des séminaires (215), 2ème étage, Bâtiment A4N

Abstract :

Spin liquids are often thought of as interacting magnetic systems which refuse to break a symmetry at any temperature. There is, however, much more to the physics of spin liquids than that- they exhibit novel and subtle properties such as algebraic correlations, topological excitations and emergent gauge fields.
Amongst the best studied examples of spin liquid physics are the spin ice materials Ho2Ti2O7 and Dy2Ti2O7, frustrated magnets on the pyrochlore lattice. Here, the spin liquid state is of a classical nature, being stabilised by its entropy. The topological excitations in spin ice take the form of magnetic monopoles and the correlations are described by an “electromagnetic » gauge field.
These discoveries in the spin ices have led to an intense research interest in other pyrochlore materials, with the goal of finding a quantum variant of the spin ices in which the spin liquid is dominated by quantum fluctuations and the T=0 ground state is a highly entangled superposition of many spin ice configurations. Experimental studies of these candidate “quantum spin ices” have revealed many unexpected properties, however, which don’t fall easily into the spin ice picture.
In this talk I will review progress in this area and present a theory of these frustrated pyrochlore materials, starting from a symmetry-based treatment of their anisotropic exchange interactions. This leads to an understanding of how competing phases govern the properties of many pyrochlore magnets, and to a prediction of completely new spin liquid phases falling outside the spin-ice paradigm.