From Spontaneous Symmetry Breaking to Topological Order

2015 International Symposium on Quantum Fluids and Solids

Speaker: J. A. Sauls
Department of Physics & Astronomy, Northwestern University, Evanston, IL 60208
August 13, 2015

Abstract: The superfluid phases of 3He provide a paradigm for the role of spontaneous symmetry breaking in quantum field theory and condensed matter physics. Recent developments in theoretical condensed matter physics emphasize an organizing principle based on topology. An exciting frontier in condensed matter physics is the search for exotic excitations - Majorana and Weyl fermions - that are signatures of topological order. In this context the ground states of the quantum liquid phases of 3He provide remarkable examples of emergent topological order, i.e. non-trivial topology of the Hilbert space of quanta that characterize classes of broken symmetry ground states. In this talk I discuss the fermionic and bosonic excitations of 2D chiral 3He-A and chiral superconductors, and their relation to broken space- and time-inversion symmetries and the emergent topology of the chiral ground state. I highlight key features of the B-phase of 3He, which is the realization of a 3D time-reversal invariant topological superfluid characterized by a spectrum of helical Majorana fermions confined on the surface and a rich spectrum of bosonic (Nambu-Goldstone and Higgs) modes that reflect the broken gauge and relative spin-orbit symmetries of the B-phase ground state. The marriage of ultra-low temperature and nano-fabrication technologies, combined with low-noise/high-precision acoustic, optical and NMR spectroscopies opens new possibilities for the study of (i) new broken symmetry states under strong confinement, as well as (ii) novel excitations reflecting topological order. I conclude with a brief overview of strategies and progress in detecting and manipulating these novel excitations in superfluid 3He and chiral superconductors.

This research was supported by NSF Grant: DMR-1106315.

Slides: [PDF]

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Last update: August, 2015