We extend our recent work [Y. Endo et al., Phys. Rev. A 92, 023610 (2015)] for a parity-mixing effect in a model of two-dimensional lattice fermions to a realistic three-dimensional ultracold Fermi gas. Including effects of broken local spatial inversion symmetry by a trap potential within the framework of the real-space Bogoliubov-de Gennes theory at
T=0, we point out that an odd-parity
p-wave Cooper-pair amplitude is expected to have already been realized in previous experiments on an (even-parity)
s-wave superfluid Fermi gas with spin imbalance. This indicates that when one suddenly changes the
s-wave pairing interaction to an appropriate
p-wave one by using a Feshbach technique in this case, a nonvanishing
p-wave superfluid order parameter is immediately obtained, which is given by the product of the
p-wave interaction and the
p-wave pair amplitude that has already been induced in the spin-imbalanced
s-wave superfluid Fermi gas. Thus, by definition, the system is in the
p-wave superfluid state, at least just after this manipulation. Since the achievement of a
p-wave superfluid state is one of the most exciting challenges in cold Fermi gas physics, our results may provide an alternative approach to this unconventional pairing state. In addition, since the parity-mixing effect cannot be explained as far as one deals with a trap potential in the local density approximation (LDA), it is considered as a crucial example which requires us to go beyond the LDA.
We propose a theoretical idea to reach the
p-wave superfluid phase in an ultracold Fermi gas. The key of our idea is that the pairing symmetry of a Fermi superfluid is fully dominated by the symmetry of the superfluid order parameter, which is essentially given by the product of a pair amplitude and a pairing interaction. Noting this, in our proposal, we first prepare a
p-wave pair amplitude not by using a
p-wave interaction, but by using the phenomenon that a
p-wave pair amplitude is induced in an
s-wave superfluid Fermi gas with antisymmetric spin-orbit interaction. In this case, although the system is still in the
s-wave superfluid state with the
s-wave superfluid order parameter, when one suddenly replaces the
s-wave interaction by an appropriate
p-wave one (which is possible in cold Fermi gases by using a Feshbach resonance technique), the product of the
p-wave interaction and the
p-wave pair amplitude that has already been prepared in the spin-orbit-coupled
s-wave superfluid state immediately gives a finite
p-wave superfluid order parameter. Thus, at least just after this manipulation, the system is in the
p-wave superfluid state, being characterized by the artificially produced
p-wave superfluid parameter. In this paper, to assess our idea, we evaluate the
p-wave pair amplitude in a spin-orbit-coupled
s-wave superfluid Fermi gas at
T=0. We determine the region where a large
p-wave pair amplitude is obtained in the phase diagram with respect to the strengths of the
s-wave pairing interaction and the spin-orbit coupling. We also discuss the accessibility of this optimal region on the viewpoint of the superfluid phase transition temperature. Since the achievement of a
p-wave superfluid Fermi gas is one of the most crucial issues in cold-atom physics, our proposal would be useful for this exciting challenge.
We theoretically propose an idea to realize a
p-wave superfluid Fermi gas. To overcome the experimental difficulty that a
p-wave pairing interaction to form
p-wave Cooper pairs damages the system before the condensation growth, we first prepare a
p-wave pair amplitude (
Φp) in a spin-orbit coupled
s-wave superfluid Fermi gas, without any
p-wave interaction. Then, by suddenly changing the
s-wave interaction with a
p-wave one (
Up) by using a Feshbach resonance, we reach the
p-wave superfluid phase with the
p-wave order parameter being symbolically written as
Δp∼UpΦp. In this letter, we assess this scenario within the framework of a time-dependent Bogoliubov-de Gennes theory. Our results would contribute to the study toward the realization of unconventional pairing states in an ultracold Fermi gas.
We theoretically investigate a spin-orbit-coupled
s-wave superfluid Fermi gas, to examine the time evolution of the system, after an
s-wave pairing interaction is replaced by a
p-wave one at
t=0. In our recent paper [T. Yamaguchi, D. Inotani, and Y. Ohashi, J. Phys. Soc. Jpn. 86, 013001 (2017)], we proposed that this manipulation may realize a
p-wave superfluid Fermi gas because the
p-wave pair amplitude that is induced in the
s-wave superfluid state by a parity-broken antisymmetric spin-orbit interaction gives a nonvanishing
p-wave superfluid order parameter, immediately after the
p-wave interaction is turned on. In this paper, using a time-dependent Bogoliubov-de Gennes theory, we assess this idea under various conditions with respect to the
s-wave and
p-wave interaction strengths, as well as the spin-orbit coupling strength. From these, we clarify that the momentum distribution of Fermi atoms in the initial
s-wave state (
t<0) is a key to produce a large
p-wave superfluid order parameter. Since the realization of a
p-wave superfluid state is one of the most exciting and difficult challenges in cold Fermi gas physics, our results may provide a possible way to accomplish this.
We consider the problem of spin-triplet
p-wave superfluid pairing with total spin projection
ms=0 in atomic Fermi gas across the Feshbach resonance. We allow for imbalanced populations and take into account the effects due to the presence of a harmonic trapping potential. Within the mean-field approximation for the one- and two-channel pairing models we show that the
p-wave superfluid state has the lowest energy up to some distance from the trap center, the distance depending on population imbalance and the side of the Feshbach resonance (BCS or BEC) the system is in. Beyond this, the system is in the normal state. Since the system, even in the presence of the harmonic trap, is invariant under O(3) space rotation, the superfluid cores which emerge in the trap are comprised of states that are degenerate with respect to the ``orbital ferromagnet'' state, ${p}_{x}\ifmmode\pm\else\textpm\fi{}i{p}_{y}$, as well as the ones in which all angular momentum components of the order parameter are nonzero, provided the modulus of the order parameter maintains a fixed magnitude.
We suggest that the exchange fluctuations close to a Feshbach resonance in a two-component Fermi gas can result in an effective p-wave attractive interaction. On the BCS side of a Feshbach resonance, the magnitude of this effective interaction is comparable to the s-wave interaction, therefore leading to a possible spin-triplet superfluid in the range of temperatures of actual experiments. We also show that the particle-hole exchange fluctuations introduce an effective scattering length which does not diverge, as the standard mean-field one does. Finally, using the effective interaction quantities we are able to model the molecular binding energy on the BEC side of the resonance.