CMT147

Electron bubbles and Weyl Fermions in chiral superfluid ³He-A

• Author(s): Oleksii Shevtsov and J. A. Sauls
• Address: Department of Physics & Astronomy, Northwestern University, Evanston, IL 60208
• Date: June 20, 2016
• Journal: Physical Review B 94, 064511 (2016) [DOI]
• Abstract: Electrons embedded in liquid ³He form mesoscopic bubbles with radii large compared to the interatomic distance between ³He atoms, voids of N_bubble≈ 200 ³He atoms, generating a negative ion with a large effective mass that scatters thermal excitations. We develop scattering theory of Bogoliubov quasiparticles by negative ions embedded in ³He-A that incorporates the broken symmetries of ³He-A, particularly time-reversal and mirror symmetry in a plane containing the chiral axis l. Multiple scattering by the ion potential, combined with Andreev scattering by the chiral order parameter, leads to a spectrum of Weyl Fermions bound to the ion that support a mass current circulating the electron bubble - the mesoscopic realization of chiral edge currents in superfluid ³He-A films. A consequence is that electron bubbles embedded in ³He-A acquire angular momentum, L ≈-(N_bubble/2) ℏ l inherited from the chiral ground state. We extend the scattering theory to calculate the forces on a moving electron bubble, both the Stokes drag and a transverse force, F_W=(e/c) v ×B_W, defined by an effective magnetic field, B_W ∝ l, generated by the scattering of thermal quasiparticles off the spectrum of Weyl Fermions bound to the moving ion. The transverse force is responsible for the anomalous Hall effect for electron bubbles driven by an electric field reported by the RIKEN group. Our results for the scattering cross section, drag and transverse forces on moving ions are compared with experiments, and shown to provide a quantitative understanding of the temperature dependence of the mobility and anomalous Hall angle for electron bubbles in normal and superfluid ³He-A. We also discuss our results in relation to earlier theoretical work on negative ions in superfluid ³He.

• Eprint: [PDF] [arXiv]

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