We investigate theoretically fermionic superfluidity induced by Feshbach resonance in the orbital p-wave channel and determine the general phase diagram. In contrast with superfluid (3)He, due to the dipole interaction, the pairing is extremely anisotropic. When this dipole interaction is relatively strong, the pairing has symmetry k(z). When it is relatively weak, it is of symmetry k(z) + ibetak(y) (up to a rotation about z;, here beta < 1). A phase transition between these two states can occur under a change in the magnetic field or the density of the gas.
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 investigate single-particle properties of a one-component Fermi gas with a tunable p-wave interaction. Including pairing fluctuations associated with this anisotropic interaction within a
T-matrix theory, we calculate the single-particle density of states, as well as the spectral weight, above the superfluid transition temperature
Tc. Starting from the weak-coupling regime, we show that the so-called pseudogap first develops in these quantities with increasing the interaction strength. However, when the interaction becomes strong to some extent, the pseudogap becomes obscure to eventually disappear in the strong-coupling regime. This non-monotonic interaction dependence is quite different from the case of an s-wave interaction, where the pseudogap simply develops with increasing the interaction strength. The difference between the two cases is shown to originate from the momentum dependence of the p-wave interaction, which vanishes in the low momentum limit. We also identify the pseudogap regime in the phase diagram with respect to the temperature and the p-wave interaction strength. Since the pseudogap is a precursor phenomenon of the superfluid phase transition, our results would be useful for the research toward the realization of p-wave superfluid Fermi gases.
We investigate the superfluid properties of a one-component Fermi gas with a uniaxially anisotropic
p-wave pairing interaction,
Ux>Uy=Uz [where
Ui(i=x,y,z) is a
pi-wave pairing interaction]. This type of interaction is considered to be realized in a
40K Fermi gas. Including pairing fluctuations within a strong-coupling
T-matrix theory, we determine the
px-wave superfluid phase transition temperature
Tcpx, as well as the other phase transition temperature
Tcpx+ipy(<Tcpx), below which the superfluid order parameter has the
px+ipy-wave symmetry. In the normal state near
Tcpx,px-wave pairing fluctuations are shown to induce an anisotropic pseudogap phenomenon, where a dip structure in the angle-resolved density of states around $\ensuremath{\omega}=0$ is the most remarkable in the
px direction. In the
px-wave superfluid phase $({T}_{\mathrm{c}}^{{p}_{x}+i{p}_{y}}<T\ensuremath{\le}{T}_{\mathrm{c}}^{{p}_{x}})$, while the pseudogap in the
px direction continuously changes to the superfluid gap, the pseudogap in the perpendicular direction to the
px axis is found to continue developing because of enhanced
py-wave and
pz-wave pairing fluctuations around the node of the
px-wave superfluid order parameter. Since pairing fluctuations are always suppressed in the isotropic
s-wave superfluid state, this phenomenon is peculiar to an unconventional Fermi superfluid with a nodal superfluid order parameter. Since the
p-wave Fermi superfluid is the most promising non-
s-wave pairing state in an ultracold Fermi gas, our results would contribute to understanding how the anisotropic pairing fluctuations, as well as the existence of plural superfluid phases, affect many-body properties of this unconventional Fermi superfluid.
We performed a theoretical investigation on the ground state properties of a two dimensional ultra-cold Fermi superfluid with an anisotropic spin-orbit coupling (SOC). In the absence of Zeeman field, the system evolves from weak coupling BCS regime to strongly interacting BEC regime (BCS-BEC crossover) with increasing either the two-particle interaction strength or SOC parameters. We focused on the behaviors of pairing parameter and density of states (DOS) when increasing the anisotropic parameter of the SOC. Surprisingly, we discovered that the gap parameter decreases with increasing the anisotropic parameters, but the DOS at the Fermi surface shows non-monotonic behavior as a function of the anisotropic parameter. In the presence of the Zeeman field, we discussed a particular type of topological phase transition by obtaining the analytical result of the topological invariant and directly related this quantum phase transition with a sudden change of the ground state wave-function. Effects of higher partial wave pairing terms on this topological phase transition were briefly discussed.
We discuss the time-of-flight expansion of dilute p-wave Fermi condensates on the BEC side of Feshbach resonances, as a way to extract information about the order parameter symmetry for superfluidity. We show that the cloud profile is in general sensitive to the interaction strength between fermions, the magnitude and direction of external magnetic fields, and to the angular momentum projection of the order parameter. In particular, due to the anisotropic nature of p-wave interactions we show that the time-of-flight expansion of a p-wave superfluid is anisotropic even if the superfluid is confined to a completely isotropic trap, unlike the case of Bose or s-wave Fermi condensates, which under the same circumstances expand isotropically. Furthermore, we demonstrate that expanding p-wave superfluids released from axially symmetric traps experience anisotropy inversions, where the aspect ratio between the axial and radial directions change during expansion, while the axial symmetry can also be lost reflecting the spatial anisotropy of the underlying interaction.