KN01 - Ground State Selection in Quantum Pyrochlore Magnets

Bruce Gaulin (McMaster University, Canada)

The pyrochlore lattice, a network of corner-sharing tetrahedra, is one of the most pervasive crystalline architectures in nature that supports geometrical frustration.  We and others have been interested in a family of rare earth pyrochlore magnets, that can display quantum S=1/2 magnetism on such a lattice.  The ground states for some of these materials may be disordered, as occurs for "spin ice", a version of this phenomena with the same frustration and degeneracy as solid ice, as well as by a quantum version of this model known as "quantum spin ice" that possesses an emergent quantum electrodynamics.  Non-colinear antiferromagnetic ground states are also expressed in rare earth pyrochlore magnets, and I will describe how this comes about and these ground states can be understood, with an emphasis on modern neutron scattering.  I'll also discuss a generalized phase diagram for the ground states of these materials, with emphasis on the Yb2Ti2O7, Er2Ti2O7, and Er2Pt2O7, and comment on how fragile some of these quantum ground states seem to be with respect to weak quenched disorder, which is hard to avoid in real materials.