Date/Time
Date(s) - 23/09/2009
3:20 pm - 4:20 pm

Title: Emergent quantum phases in novel frustrated spin 1/2 antiferromagnets

Speaker: Dr. Michael Lawler – Cornell University

Institute: Cornell University – Physics Department

Location: ABB 102

Description:

The search for new phases of matter is one of the most important pursuits in condensed matter physics. New phases can challenge existing paradigms, and open the door to fundamentally new collective behavior of many particles. One promising direction for this search is through the successful fabrication of frustrated spin 1/2 antiferromagnets. In these materials, the spins are said to be frustrated because they cannot decide in which direction they want to point. Due to the spin 1/2 moments, however, the laws of quantum mechanics may directly help the spins decide what they want to do. One possibility is that the spins form a “quantum spin liquid” phase that is governed by a new emergent spin 1/2 particle called a “spinon”. Another possibility is that neighboring spin 1/2 moments pair up into singlets and form a “valence -bond-solid” (VBS) phase governed by spin 1 triplet excitations called a “triplon”.

In this talk, I will present a review of this subject and focus on a new family of materials with spin 1/2 moments on a kagome lattice dubbed “Zn-Paratacamite”. It has been proposed that these materials contain both VBS and spin liquid phases. I will argue that this is the case based on a theory of quark-like spin 1/2 spinons binding into spin 1 triplons and from numerical diagonalization of model Hamiltonians of small systems. In addition, I will present predictions for future experiments to test our theory.