πjunction and spontaneous current state in a superfluid Fermi gas

Abstract

We discuss an idea to realize a spontaneous current in a superfluid Fermi gas. When a polarized Fermi superfluid (N ↑ > N ↓ , where N σ is the number of atoms in the hyperfine state described by pseudospin σ =↑, ↓.) is loaded onto a ring-shaped trap with a weak potential barrier, some of excess atoms (∆N = N ↑ −N ↓ ) are localized around the barrier. As shown in our previous paper [T.Kashimura, S. Tsuchiya, and Y. Ohashi, Phys. Rev. A 82, 033617 (2010)], this polarized potential barrier works as a π-junction in the sense that the superfluid order parameter changes its sign across the barrier. Because of this, the phase of the superfluid order parameter outside the junction is shown to be twisted by π along the ring, which naturally leads to a circulating supercurrent. While the ordinary supercurrent state is obtained as a metastable state, this spontaneous current state is shown to be more stable than the case with no current. Our results indicate that localized excess atoms would be useful for the manipulation of the superfluid order parameter in cold Fermi gases.

Rotating Fulde-Ferrell-Larkin-Ovchinnikov state in cold Fermi gases

“…It is expected that another novel FFLO state is stabilized by the rotation. A related work has been given by Kashimura et al They showed that a spontaneous current appears in a toroidal trap with a potential barrier [26], but they didn't investigate the effect of rotation. In this paper, we investigate the FFLO phases induced by the rotation.…”

Spontaneous Currents in a Bosonic Ring

“…Such currents have recently been observed in superconducting networks [6]. Realization of this idea in superfluid fermionic cold gases in a ring-shaped trap has been proposed [7].…”

Persistent currents in rings of ultracold fermionic atoms

“…This presents an exciting opportunity to study the Kibble-Zurek mechanism with fermions [33] in the annular geometry originally proposed by Zurek [34]. These experiments were conducted with an unpolarized Fermi gas in a ring, but a weakly polarized gas could enable the creation of matter-wave circuits with π-Josephson junctions [35] and provide a new opportunity to search for exotic spin-polarized superfluid phases [36,37]. Finally, the tight transverse confinement achieved in these experiments is not far from the quasi-1D limit, and it may be feasible to create 1D quantum rings [38] of fermions with tunable interactions, where non-Fermi-liquid behavior is expected and parity effects can be significant [39].…”