Physics Colloquium as part of ``SaulsFest'' at Northwestern, October 14, 2022 Authors: J. A. Sauls
Where: Department of Physics & Astronomy, Northwestern University, Evanston, IL
October 14, 2022

Abstract: Parity violation by the weak force was demonstrated in an experiment led by Chien-Shiung Wu in 1957 on the asymmetry of electron currents emitted in the beta decay of polarized ⁶⁰Co. That asymmetry reflected two broken symmetries - mirror refelctions and time-reversal, the latter imposed by an external magnetic field. That same year Bardeen, Cooper and Schrieffer published the celebrated BCS theory of superconductivity, and soon thereafter Anderson and Morel proposed that the ground-state of liquid ³He was likely a BCS condensate of chiral molecular pairs of Helium atoms, exhibiting spontaneously broken mirror reflection and time-reversal symmetries. Indeed the high-pressure phase, superfluid ³He-A, discovered fifty years ago, is the realization of the Anderson-Morel state. However, experimental proof that the ground state of liquid ³He spontaneously breaks mirror and time-reversal symmetry had to wait until 2012 and the observation the asymmetry in motion of electrons moving in the chiral vacuum of liquid ³He. I discuss the physics behind this phenomenon, its discovery and specifically how broken symmetry and topology of the superfluid vacuum conspire to endow electrons in the chiral vacuum with ``handedness''.

This research was supported by NSF Grant: DMR-1508730

1. O. Shevtsov and J. A. Sauls,  Electron bubbles and Weyl Fermions in chiral superfluid ³He-A Phys. Rev. B 94, 064511 (2016)
2. J. A. Sauls,  On the Excitations of a Balian-Werthamer Superconductor J. Low Temp. Phys. 208, 87–118 (2022)

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