On the Excitations of a Balian-Werthamer Superconductor

Abstract

My contribution to this collection of articles in honor of David Lee and John Reppy on their 90th birthdays is a reflection on the remarkable phenomenology of the excitation spectra of superfluid ${}^3$He, in particular the B-phase which was identified by NMR and acoustic spectroscopy as Balian-Werthamer state shown in 1963 to be the ground state of a spin-triplet, p-wave superconductor within weak-coupling BCS theory. The superfluid phases of ${}^3$He provide paradigms for electronic superconductors with broken space-time symmetries and non-trivial ground-state topology. Indeed broken spin- and orbital rotation symmetries lead to a rich spectrum of collective modes of the order parameter that can be detected using NMR, acoustic and microwave spectroscopies. The topology of the BW state implies its low-temperature, low-energy transport properties are dominated by gapless Majorana modes confined on boundaries or interfaces. Given the central role the BW state played I discuss the acoustic and electromagnetic signatures of the BW state, the latter being relevant if an electronic analog of superfluid ${}^3$He-B is realized.

Tribute to David Lee and John Reppy on their 90th birthdays; 16 pages, 5 figures

References in corpus (6)

• Classification of topological insulators and superconductors in three spatial dimensions
• Symmetry Protected Topological Order and Spin Susceptibility in Superfluid 3He-B
• Light Quantum Control of Persisting Higgs Modes in Iron-Based Superconductors
• Discovery of an Excited Pair State in Superfluid 3He
• On Nambu's Fermion-Boson Relations for Superfluid ${}^3$He-B
• Anisotropy and Strong-Coupling Effects on the Collective Mode Spectrum of Chiral Superconductors: Application to Sr${}_2$RuO${}_4$

Cited by in corpus (2)

• Linear optical response from the odd parity Bardasis-Schrieffer mode in locally non-centrosymmetric superconductors
• Quantum Quenches of an SO(5) Pseudospin Reveal Higgs Bosons