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2015 International Symposium on Quantum Fluids and Solids
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Speaker: J. A. Sauls

Department of Physics & Astronomy, Northwestern University, Evanston, IL 60208

August 13, 2015

**Abstract:**
The superfluid phases of ^{3}He 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 ^{3}He 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 ^{3}He-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 ^{3}He, 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 ^{3}He and chiral superconductors.

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

**Slides:**
[PDF]

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