Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

International Symposium on Access Spaces (ISAS)

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

Takashi Kashimura, Shunji Tsuchiya, Yoji Ohashi

Published Jun 1, 2011• 0 citations
Publisher

Abstract

We investigate the stability of π-phase in a polarized superfluid Fermi gas (N↑>; N↓, where Nσis the number of atoms in the hyperfine state described by pseudospin-σ). In our previous paper [T. Kashimura, S. Tsuchiya, and Y. Ohashi, Phys. Rev. A 82, 033617 (2010)], we showed that excess atoms (ΔN = N↑- N↓) localized around a potential barrier embedded in the system induces the π-phase at T = 0, where the phase of superfluid order parameter differ by π across the junction. In this paper, we extend our previous work to include temperature effects within the mean-field theory. We show that the π-phase is stable even at finite temperatures, although transition from the π-phase to 0-phase eventually occurs at a certain temperature. Our results indicate that the π-phase is experimentally accessible in cold Fermi gases.

DOI
10.1109/isas.2011.5960916

Related papers

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

Takashi Kashimura, Shunji Tsuchiya, Yoji Ohashi

We investigate the stability of $π$-phase in a polarized superfluid Fermi gas ($N_\uparrow>N_\downarrow$, where $N_σ$ is the number of atoms in the hyperfine state described by pseudospin-$σ$). In our previous paper [T. Kashimura, S. Tsuchiya, and Y. Ohashi, Phys. Rev. A {\bf 82}, 033617 (2010)], we showed that excess atoms ($ΔN=N_\uparrow-N_\downarrow$) localized around a potential barrier embedded in the system induces the $π$-phase at T=0, where the phase of superfluid order parameter differ by $π$ across the junction. In this paper, we extend our previous work to include temperature effects within the mean-field theory. We show that the $π$-phase is stable even at finite temperatures, although transition from the $π$-phase to 0-phase eventually occurs at a certain temperature. Our results indicate that the $π$-phase is experimentally accessible in cold Fermi gases.

arXiv:1107.0105•Jul 1, 2011•0 citations

Superfluid-ferromagnet-superfluid junction and the π phase in a superfluid Fermi gas

Takashi Kashimura, Shunji Tsuchiya, Yoji Ohashi

We investigate the possibility of a 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 (${N}_{\ensuremath{\uparrow}}>{N}_{\ensuremath{\downarrow}}$, where ${N}_{\ensuremath{\sigma}}$ is the number of atoms with pseudospin $\ensuremath{\sigma}= \ensuremath{\uparrow}$, $\ensuremath{\downarrow}$), this barrier is shown to be magnetized in the sense that excess $\ensuremath{\uparrow}$-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 $\ensuremath{\pi}$ 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.

arXiv:1006.3673•Physical Review A•Sep 24, 2010•4 citations

π junction and spontaneous current state in a superfluid Fermi gas

Takashi Kashimura, Shunji Tsuchiya, Yoji Ohashi

We discuss an idea to realize a spontaneous current in a superfluid Fermi gas. When a polarized Fermi superfluid (${N}_{\ensuremath{\uparrow}}>{N}_{\ensuremath{\downarrow}}$, where ${N}_{\ensuremath{\sigma}}$ is the number of atoms in the hyperfine state described by pseudospin $\ensuremath{\sigma}=\ensuremath{\uparrow},\ensuremath{\downarrow}$) is loaded onto a ring-shaped trap with a weak potential barrier, some excess atoms ($\ensuremath{\Delta}N={N}_{\ensuremath{\uparrow}}\ensuremath{-}{N}_{\ensuremath{\downarrow}}$) 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 $\ensuremath{\pi}$ 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 $\ensuremath{\pi}$ 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.

arXiv:1105.4023•Physical Review A•Jul 20, 2011•4 citations

π-phase and Spontaneous Supercurrent induced by Pseudo-ferromagnetic Junction in a Spin-polarized Superfluid Fermi Gas

Takashi Kashimura, Shunji Tsuchiya, Yoji Ohashi

We theoretically investigate a possible spontaneous current state in a polarized superfluid Fermi gas confined in a toroidal trap. When one puts a weak nonmagnetic potential barrier in this system, this barrier is known to be magnetized in the sense that some of excess ↑-spin atoms are localized around it (where the ↑-spin describes the majority component of the polarized Fermi gas). Using this unique property, we show that this magnetized barrier, or the pseudo-ferromagnetic junction, induces a spontaneous current circulating along the toroidal trap. While the ordinary supercurrent state appears as a metastable state, this spontaneous current state is realized as the most stable state, originating from the phase twist of the superfluid order parameter by the magnetized potential barrier.

Journal of Physics Conference Series•Dec 17, 2012•0 citations

Finite-temperature phase diagram of a two-component Fermi gas with density imbalance

Lianyi He, Meng Jin, Pengfei Zhuang

We investigated possible superfluid phases at finite temperature in a two-component Fermi gas with density imbalance. In the frame of a general four-fermion interaction theory, we solved in the BCS region the gap equations for the pairing gap and pairing momentum under the restriction of fixed number densities and analyzed the stability of different phases by calculating the superfluid density and number susceptibilities. The homogeneous superfluid is stable only at high temperature and low number asymmetry, the inhomogeneous Larkin-Ovchinnikov-Fudde-Ferrell state survives at low temperature and high number asymmetry, and in between them there exists another possible inhomogeneous phase, that of phase separation. The critical temperatures and the orders of the phase transitions among the superfluid phases and normal phase are calculated analytically and numerically. The phase diagram we obtained in the temperature and number asymmetry plane is quite different from the one in the temperature and chemical potential difference plane for a system with fixed chemical potentials.

arXiv:cond-mat/0606322•Physical Review B•Dec 22, 2006•40 citations

Formation of magnetic impurities and pair-breaking effect in a superfluid Fermi gas

Yoji Ohashi

We theoretically investigate the introduction of magnetic impurities into a superfluid Fermi gas. In the presence of a population imbalance (${N}_{\ensuremath{\uparrow}}>{N}_{\ensuremath{\downarrow}}$, where ${N}_{\ensuremath{\sigma}}$ is the number of Fermi atoms with pseudospin $\ensuremath{\sigma}=\ensuremath{\uparrow},\ensuremath{\downarrow}$), we show that nonmagnetic potential scatterers embedded in the system are magnetized in the sense that some of the excess spin-$\ensuremath{\uparrow}$ atoms are localized around them. They destroy the superfluid order parameter around them, as in the case of the magnetic impurity effect discussed in the superconductivity literature. This pair-breaking effect naturally leads to localized excited states below the superfluid excitation gap. To confirm our idea in a simple manner, we consider an attractive Fermi-Hubbard model within the mean-field theory at $T=0$. We determine consistent superfluid properties around a nonmagnetic impurity, such as the superfluid order parameter, local population imbalance, as well as the single-particle density of states, in the presence of a population imbalance. Since competition between superconductivity and magnetism is one of the most fundamental problems in condensed-matter physics, our results would be useful for the study of this important issue in cold Fermi gases.

arXiv:1103.1942•Physical Review A•Jun 10, 2011•12 citations
We investigate the stability of π-phase in a polarized superfluid Fermi gas (N↑>; N↓, where Nσis the number of atoms in the hyperfine state described by pseudospin-σ). In our previous paper [T. Kashimura, S. Tsuchiya, and Y. Ohashi, Phys. Rev. A 82, 033617 (2010)], we showed that excess atoms (ΔN = N↑- N↓) localized around a potential barrier embedded in the system induces the π-phase at T = 0, where the phase of superfluid order parameter differ by π across the junction. In this paper, we extend our previous work to include temperature effects within the mean-field theory. We show that the π-phase is stable even at finite temperatures, although transition from the π-phase to 0-phase eventually occurs at a certain temperature. Our results indicate that the π-phase is experimentally accessible in cold Fermi gases.
Superfluid/ferromagnet/superfluid-junction and πππ-phase in a superfluid Fermi gas at finite temperatures
We investigate the stability of πππ-phase in a polarized superfluid Fermi gas (N↑>N↓N_\uparrow>N_\downarrowN↑​>N↓​, where NσN_σNσ​ is the number of atoms in the hyperfine state described by pseudospin-σσσ). In our previous paper [T. Kashimura, S. Tsuchiya, and Y. Ohashi, Phys. Rev. A {\bf 82}, 033617 (2010)], we showed that excess atoms (ΔN=N↑−N↓ΔN=N_\uparrow-N_\downarrowΔN=N↑​−N↓​) localized around a potential barrier embedded in the system induces the πππ-phase at T=0, where the phase of superfluid order parameter differ by πππ across the junction. In this paper, we extend our previous work to include temperature effects within the mean-field theory. We show that the πππ-phase is stable even at finite temperatures, although transition from the πππ-phase to 0-phase eventually occurs at a certain temperature. Our results indicate that the πππ-phase is experimentally accessible in cold Fermi gases.
We investigate the possibility of a 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=0T=0T=0 within the mean-field theory. When a potential barrier is embedded in a superfluid Fermi gas with population imbalance (${N}_{\ensuremath{\uparrow}}>{N}_{\ensuremath{\downarrow}}$, where ${N}_{\ensuremath{\sigma}}$ is the number of atoms with pseudospin $\ensuremath{\sigma}= \ensuremath{\uparrow}$, $\ensuremath{\downarrow}$), this barrier is shown to be magnetized in the sense that excess $\ensuremath{\uparrow}$-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 $\ensuremath{\pi}$ 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.
We discuss an idea to realize a spontaneous current in a superfluid Fermi gas. When a polarized Fermi superfluid (${N}_{\ensuremath{\uparrow}}>{N}_{\ensuremath{\downarrow}}$, where ${N}_{\ensuremath{\sigma}}$ is the number of atoms in the hyperfine state described by pseudospin $\ensuremath{\sigma}=\ensuremath{\uparrow},\ensuremath{\downarrow}$) is loaded onto a ring-shaped trap with a weak potential barrier, some excess atoms ($\ensuremath{\Delta}N={N}_{\ensuremath{\uparrow}}\ensuremath{-}{N}_{\ensuremath{\downarrow}}$) 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 $\ensuremath{\pi}$ 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 $\ensuremath{\pi}$ 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.
We theoretically investigate a possible spontaneous current state in a polarized superfluid Fermi gas confined in a toroidal trap. When one puts a weak nonmagnetic potential barrier in this system, this barrier is known to be magnetized in the sense that some of excess ↑-spin atoms are localized around it (where the ↑-spin describes the majority component of the polarized Fermi gas). Using this unique property, we show that this magnetized barrier, or the pseudo-ferromagnetic junction, induces a spontaneous current circulating along the toroidal trap. While the ordinary supercurrent state appears as a metastable state, this spontaneous current state is realized as the most stable state, originating from the phase twist of the superfluid order parameter by the magnetized potential barrier.
We investigated possible superfluid phases at finite temperature in a two-component Fermi gas with density imbalance. In the frame of a general four-fermion interaction theory, we solved in the BCS region the gap equations for the pairing gap and pairing momentum under the restriction of fixed number densities and analyzed the stability of different phases by calculating the superfluid density and number susceptibilities. The homogeneous superfluid is stable only at high temperature and low number asymmetry, the inhomogeneous Larkin-Ovchinnikov-Fudde-Ferrell state survives at low temperature and high number asymmetry, and in between them there exists another possible inhomogeneous phase, that of phase separation. The critical temperatures and the orders of the phase transitions among the superfluid phases and normal phase are calculated analytically and numerically. The phase diagram we obtained in the temperature and number asymmetry plane is quite different from the one in the temperature and chemical potential difference plane for a system with fixed chemical potentials.
We theoretically investigate the introduction of magnetic impurities into a superfluid Fermi gas. In the presence of a population imbalance (${N}_{\ensuremath{\uparrow}}>{N}_{\ensuremath{\downarrow}}$, where ${N}_{\ensuremath{\sigma}}$ is the number of Fermi atoms with pseudospin $\ensuremath{\sigma}=\ensuremath{\uparrow},\ensuremath{\downarrow}$), we show that nonmagnetic potential scatterers embedded in the system are magnetized in the sense that some of the excess spin-$\ensuremath{\uparrow}$ atoms are localized around them. They destroy the superfluid order parameter around them, as in the case of the magnetic impurity effect discussed in the superconductivity literature. This pair-breaking effect naturally leads to localized excited states below the superfluid excitation gap. To confirm our idea in a simple manner, we consider an attractive Fermi-Hubbard model within the mean-field theory at T=0T=0T=0. We determine consistent superfluid properties around a nonmagnetic impurity, such as the superfluid order parameter, local population imbalance, as well as the single-particle density of states, in the presence of a population imbalance. Since competition between superconductivity and magnetism is one of the most fundamental problems in condensed-matter physics, our results would be useful for the study of this important issue in cold Fermi gases.