Physics at the Falls: Pairing Phenomena from Neutron Stars to Cold Atoms
State University of New York at Buffalo

Speaker: J. A. Sauls
Department of Physics & Astronomy, Northwestern University, Evanston, IL 60208
March 24, 2016

Abstract: The superfluid phases of ³He are a paradigm for spontaneous symmetry breaking in quantum field theory and condensed matter physics. Recent developments in condensed matter physics emphasize a new organizing principle based on topology. A frontier in condensed matter physics is the theoretical classification, experimental detection and characterization of exotic edge excitations - Majorana and Weyl fermions - that are signatures of topological order. I discuss signatures of broken space-time symmetries - rotations, parity and time-reversal (BTRS) - and their connections with topological order for the ground-states of superfluid ³He, Sr₂RuO₄ and UPt₃ [1]. I highlight recent experimental observations of BTRS in the heavy fermion superconductor UPt₃ and the chiral A-phase of ³He. The former is the observation of an optical polar Kerr effect [2], while the latter is based on the measurement of an anomalous Hall effect for negative ions in ³He-A [3]. I outline a theory of the anomalous Hall mobility of electrons in ³He-A, and show that the experimental results provide a direct observation of Weyl Fermions and topological order in ³He-A.

1. J. A. Sauls, Phys. Rev. B 84, 214509 (2011).
2. E. R. Schemm, et al. Science 345, 190 (2014).
3. H. Ikegami, Y. Tsutsumi, and K. Kono, Science 341, 59 (2013).
4. J. A. Sauls, Hao Wu and S-B. Chung, Front. Phys. 3:36 (2015).

Research supported by National Science Foundation Grant: DMR-1508730.

Slides: [PDF]

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