Interactions between electrons in condensed matter systems are always present, and every property of a material is fundamentally determined by this fact. In the most basic materials the collective behavior of the electrons can be projected into a language of emergent particles; phonons in a crystal, magnons in a ferromagnet, quasiparticles in a metal. However, in complex materials where there are multiple channels of interaction of comparable magnitude, it remains unclear what this single-particle language is or whether it exists at all. In this colloquium, I discuss some of the challenges and surprises that arise in a few classes of these systems, with a special focus on unconventional superconductors.
Zoom recording of talk: https://osu.app.box.com/file/714807700106
