Fermion transfer by vortex tunneling

I. K. Karpenko

Григорий Ефимович Воловик

Vortex mass in Fermi superfluids and superconductors and its influence on quantum tunneling of vortices are discussed. The vortex mass is essentially enhanced due to the fermion zero modes in the core of the vortex: the bound states of the Bogoliubov quasiparticles localized in the core. These bound states form the normal component, which is nonzero even in the low-temperature limit. In the collisionless regime ω 0 τ≫1 the normal component trapped by the vortex is unbound from the normal component in a bulk superfluid/superconductor and adds to the inertial mass of the moving vortex. In a d-wave superconductor the vortex mass has an additional factor of (B c2/B)1/2 due to the gap nodes.

Alice Bellettini, Vittorio Penna

Abstract Recently, cold atoms mixtures have attracted broad interest due to their novel and exotic quantum effects with respect to single‐component systems. In this study, the focus is on massive many‐vortex states and their dynamics. Vortex configurations characterized by the same discrete rotational symmetry are investigated when confined within topologically nonequivalent geometries, and the relative stability properties at varying number of vortices and infilling mass are highlighted. It is numerically shown how massive many‐vortex systems, in a mixture of Bose–Einstein condensates, can host the bosonic tunneling of the infilling component both in a disordered way, with tunneling events involving two or more close vortices, or in an almost‐periodic way when the vortices are organized in persisting necklaces or star‐lattices. The purpose is to explore a variety of situations involving the interplay between the highly‐nonlinear vortex dynamics and the inter‐vortex atomic transfer, and so to better understand the conditions for the onset of Josephson supercurrents in rotating systems, or to reveal phenomena that can be of interest for a future application, e.g., in the context of atomtronics.

Л. П. Рапопорт, A.G. Krylovetskii

Eugen Šimánek

Starting from the time-dependent version of the Feynman-Hellmann theorem, the Magnus force acting on a vortex in fermion superfluid is expressed via the adiabatic curvature over the space of vortex positions. With use of the Bogoliubov--de Gennes approximation, the Magnus force in a homogeneous superfluid at T=0 is shown to originate from virtual transitions between the lowest quasiparticle core bound states. Nonadiabatic corrections to the curvature are obtained to second order in vortex velocity. The adiabatic approximation is shown to break down at a critical velocity equal to the vortex velocity in the first Landau level. The effect of elastic scattering on the Magnus force is discussed in terms of the relaxation-time approximation. It is suggested that this approximation is appropriate only for a large-scale vortex motion. In this case, the effective Magnus force is drastically reduced when the elastic-scattering rate exceeds the core excitation frequency. We conjecture that quantum vortex tunneling is governed by a local Magnus force obtained from the Berry phase approach.

I. K. Karpenko