We investigate many-body phase diagrams of atomic boson-fermion mixtures loaded in the two-dimensional optical lattice. Bosons mediate an attractive, finite-range interaction between fermions, leading to fermion pairing phases of different orbital symmetries. Specifically, we show that by properly tuning atomic and lattice parameters it is possible to create superfluids with
s-,
p-, and
d-wave pairing symmetry as well as spin and charge density wave phases. These phases and their stability are analyzed within the mean-field approximation for systems of $^{40}\mathrm{K}\text{\ensuremath{-}}^{87}\mathrm{Rb}$ and $^{40}\mathrm{K}\text{\ensuremath{-}}^{23}\mathrm{Na}$ mixtures. For the experimentally accessible regime of parameters, superfluids with unconventional fermion pairing have transition temperature around a percent of the Fermi energy.
The recent experimental progress in realizing Bose-Fermi mixtures and dipolar quantum gases has created the exciting possibility of creating dipolar Bose-Fermi mixtures with intriguing and unique properties. In a dipolar condensate, the dipole-dipole interaction represents a control knob inaccessible to nondipolar Bosons. Thus, mixing dipolar bosons with fermions may open up new possibilities for creating superfluids with unconventional pairings. We consider a mixture of a spin-polarized Fermi gas and a dipolar Bose-Einstein condensate in a three-dimensional setting in which s-wave scattering between fermions and the quasiparticles of the dipolar condensate can result in an effective attractive Fermi-Fermi interaction anisotropic in nature and tunable by the dipolar interaction. We develop a procedure which allows us to determine the parameters such as densities and scattering lengths that are required to achieve optimal critical temperature before the system starts to phase separate. We perform a systematic investigation, finding that a superfluid with a critical temperature, that is orders of magnitude higher than achievable in nondipolar mixtures, can be realized in dipolar mixtures at experimentally accessible densities and scattering lengths before the system phase separates.
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 study fermionic superfluidity in a boson-single-species-fermion cold-atom mixture. We argue that apart from the standard
p-wave fermion pairing mediated by the phonon field of the boson gas, the system also exhibits
s-wave pairing with the anomalous correlator being an odd function of time or frequency. We show that such a superfluid phase can have a much higher transition temperature than the
p-wave and may exist for sufficiently strong couplings between fermions and bosons. These conditions for odd-frequency pairing are favorable close to the value of the coupling at which the mixture phase separates. We evaluate the critical temperatures for this system and discuss the experimental realization of this superfluid in ultracold atomic gases.
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 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.