Superfluid-ferromagnet-superfluid junction and theπphase in a superfluid Fermi gas

Abstract

We investigate the possibility of superfluid/ferromagnet/superfluid (SFS)-junction in a superfluid Fermi gas. To examine this possibility in a simple manner, we consider an attractive Hubbard model at T = 0 within the mean-field theory. When a potential barrier is embedded in a superfluid Fermi gas with population imbalance (N ↑ > N ↓ , where N σ is the number of atoms with pseudospin σ =↑, ↓), this barrier is shown to be magnetized in the sense that excess ↑-spin atoms are localized around it. The resulting superfluid Fermi gas is spatially divided into two by this ferromagnet, so that one obtains a junction similar to the superconductor/ferromagnet/superconductor-junction discussed in superconductivity. Indeed, we show that the so-called π-phase, which is a typical phenomenon in the SFS-junction, is realized, where the superfluid order parameter changes its sign across the junction. Our results would be useful for the study of magnetic effects on fermion superfluidity using an ultracold Fermi gas.

πjunction and spontaneous current state in a superfluid Fermi gas

“…As shown in our previous paper [20], when a nonmagnetic potential barrier is put in a superfluid Fermi gas with Model superfluid Fermi gas in a ring-shaped torus trap with a weak nonmagnetic potential barrier.…”

“…For more details, we refer to Ref. [20]. Introducing the superfluid order parameter ∆ i = U ĉ i,↓ĉi,↑ , as well as the particle densities n i,σ (σ =↑, ↓), we obtain the mean-field Hamiltonian for Eq.…”

Superfluid/ferromagnet/superfluid-junction and π-phase in a superfluid Fermi gas at finite temperatures

“…In this paper, we extend our previous work at = 0 [11] to the case of finite temperatures. Since experiments are always done at finite temperatures, this extension is important to clarify to what extent the SFS-junction, as well as the -phase, are stable against thermal effects.…”

“…In our previous paper [11], as another application of superfluid Fermi gases to condensed matter physics, we theoretically proposed an idea to simulate a superfluid/ferromagnet/superfluid (SFS)-junction. By numerically solving the mean-field Bogoliubov-de Gennes theory in real space at = 0, we showed that, when we put a nonmagnetic potential barrier in a polarized superfluid Fermi gas ( ↑ > ↓ , where is the number of Fermi atoms in the atomic hyperfine state described by pseudospin-), it is magnetized in the sense that some of excess ↑-spin atoms are localized around it.…”

“…In our previous paper [11], as another application of superfluid Fermi gases to condensed matter physics, T. Kashimura is with Department of Physics, Keio University, Yokohama, Japan. (E-mail:t.kashimura@a3.keio.jp) S. Tsuchiya is with Department of Physics, Tokyo University of Science, Tokyo, Japan, and CREST(JST), Saitama, Japan.…”