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. At its heart, this colloquium will be about symmetry and thermodynamics. 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. And finally, the confluence of new measurement techniques and new materials also leads to possibilities for new applications; I will briefly outline one such application, based on a giant elastocaloric effect. Multipolar order, it would seem, is not only interesting from a fundamental perspective, but can also be useful.
Ian Fisher is a Professor of Applied Physics at Stanford University, working in the general area of experimental condensed matter physics. In recent years, his research has emphasized novel ways in which externally induced strains can be used to couple to and manipulate a variety of exotic electronic states, revealing essential aspects of their causes and consequences.