<B>Faculty Candidate Seminar</B><br><i>Collective Behavior From Top to Bottom: Stable Phases Without Quasiparticles in Quantum Magnets</i>

Speaker: Professor Michael Hermele (University of Colorado at Boulder)

Condensed matter systems are built from large numbers of simple, microscopic constituents, such as electrons in a solid or atoms in a trap. Even when interactions among these constituents are very strong, it is a well-known but remarkable fact that the low-energy physics can very often be understood in terms of weakly interacting particle-like objects known as quasiparticles. The quasiparticle concept is one of the pillars of the understanding of quantum condensed matter. However, in many strongly correlated systems there is substantial experimental evidence calling the validity of a quasiparticle picture into question.

In this talk, I will discuss theoretical work on "algebraic spin liquids," a class of stable zero-temperature states of matter that lack quasiparticles, even at the lowest energies. The systems considered are two-dimensional frustrated magnetic insulators, which are relatively simple in that one need only deal with the electron's spin, but not its charge. In addition to describing some of the remarkable observable signatures of algebraic spin liquids, I will explain why they are good candidates for the long-sought ground state of the kagome lattice antiferromagnet, and how they may be relevant for recent experiments on ZnCu3(OH)6Cl2.