High rank multipole order: feeling the strain

Interactions can lead to a wide variety of ordered states in materials. Phase transitions in which local atomic states develop spontaneous high rank multipole order provides a particularly rich arena for new insights. A key element in the study of such systems is the ability to couple to the associated order parameter.

I will describe how one can couple to a variety of different multipolar states, motivating new methodologies to measure a fundamental thermodynamic material property, the multipole susceptibility. One can also identify effective transverse fields, which, when applied inside the ordered state, induce quantum fluctuations and can drive a multipolar quantum phase transition. I will explain the very special roles that strain can play for each of the cases, and will outline new experimental approaches in which the materials 'feel the strain' in different ways.

Even while we manipulate the crystal lattice to tune electronic order, hyperfine interactions are not always completely innocent. Along the way I will introduce the special case of an electro-nuclear quantum phase transition.