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 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.

arXiv:1504.03835Physical Review AJul 13, 20159 citations

Pairing fluctuations and an anisotropic pseudogap phenomenon in an ultracold superfluid Fermi gas with plural p -wave superfluid phases

Daisuke Inotani, Yoji Ohashi

We investigate the superfluid properties of a one-component Fermi gas with a uniaxially anisotropic $p$ -wave pairing interaction, ${U}_{x}>{U}_{y}={U}_{z}$ [where ${U}_{i}\phantom{\rule{0.28em}{0ex}}(i=x,y,z)$ is a ${p}_{i}$ -wave pairing interaction]. This type of interaction is considered to be realized in a $^{40}\mathrm{K}$ Fermi gas. Including pairing fluctuations within a strong-coupling $T$ -matrix theory, we determine the ${p}_{x}$ -wave superfluid phase transition temperature ${T}_{\mathrm{c}}^{{p}_{x}}$ , as well as the other phase transition temperature ${T}_{\mathrm{c}}^{{p}_{x}+i{p}_{y}}\phantom{\rule{0.28em}{0ex}}(<{T}_{\mathrm{c}}^{{p}_{x}})$ , below which the superfluid order parameter has the ${p}_{x}+i{p}_{y}$ -wave symmetry. In the normal state near ${T}_{\mathrm{c}}^{{p}_{x}}, {p}_{x}$ -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 ${p}_{x}$ direction. In the ${p}_{x}$ -wave superfluid phase $({T}_{\mathrm{c}}^{{p}_{x}+i{p}_{y}}<T\ensuremath{\le}{T}_{\mathrm{c}}^{{p}_{x}})$, while the pseudogap in the ${p}_{x}$ direction continuously changes to the superfluid gap, the pseudogap in the perpendicular direction to the ${p}_{x}$ axis is found to continue developing because of enhanced ${p}_{y}$ -wave and ${p}_{z}$ -wave pairing fluctuations around the node of the ${p}_{x}$ -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 investigate the superfluid properties of a one-component Fermi gas with a uniaxially anisotropic $p$-wave pairing interaction, ${U}_{x}>{U}_{y}={U}_{z}$ [where ${U}_{i}\phantom{\rule{0.28em}{0ex}}(i=x,y,z)$ is a ${p}_{i}$-wave pairing interaction]. This type of interaction is considered to be realized in a $^{40}\mathrm{K}$ Fermi gas. Including pairing fluctuations within a strong-coupling $T$-matrix theory, we determine the ${p}_{x}$-wave superfluid phase transition temperature ${T}_{\mathrm{c}}^{{p}_{x}}$, as well as the other phase transition temperature ${T}_{\mathrm{c}}^{{p}_{x}+i{p}_{y}}\phantom{\rule{0.28em}{0ex}}(<{T}_{\mathrm{c}}^{{p}_{x}})$, below which the superfluid order parameter has the ${p}_{x}+i{p}_{y}$-wave symmetry. In the normal state near ${T}_{\mathrm{c}}^{{p}_{x}}, {p}_{x}$-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 ${p}_{x}$ direction. In the ${p}_{x}$-wave superfluid phase $({T}_{\mathrm{c}}^{{p}_{x}+i{p}_{y}}<T\ensuremath{\le}{T}_{\mathrm{c}}^{{p}_{x}})$, while the pseudogap in the ${p}_{x}$ direction continuously changes to the superfluid gap, the pseudogap in the perpendicular direction to the ${p}_{x}$ axis is found to continue developing because of enhanced ${p}_{y}$-wave and ${p}_{z}$-wave pairing fluctuations around the node of the ${p}_{x}$-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.

arXiv:1508.06691Physical Review ADec 30, 201512 citations

Microscopic superfluidity

ScienceMar 27, 19980 citations

Superfluid Physics

Cecil T. Lane, E. Maxwell

American Journal of PhysicsJan 1, 19630 citations

Appropriate conditions to realize a p -wave superfluid state starting from a spin-orbit-coupled s -wave superfluid Fermi gas

T. Yamaguchi, Daisuke Inotani, Yoji Ohashi

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 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.

arXiv:1701.08255Physical Review AMay 9, 20170 citations

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 the superfluid properties of a one-component Fermi gas with a uniaxially anisotropic

p

-wave pairing interaction,

{U}_{x}>{U}_{y}={U}_{z}

[where

{U}_{i}\phantom{\rule{0.28em}{0ex}}(i=x,y,z)

is a

{p}_{i}

-wave pairing interaction]. This type of interaction is considered to be realized in a

^{40}\mathrm{K}

Fermi gas. Including pairing fluctuations within a strong-coupling

T

-matrix theory, we determine the

{p}_{x}

-wave superfluid phase transition temperature

{T}_{\mathrm{c}}^{{p}_{x}}

, as well as the other phase transition temperature

{T}_{\mathrm{c}}^{{p}_{x}+i{p}_{y}}\phantom{\rule{0.28em}{0ex}}(<{T}_{\mathrm{c}}^{{p}_{x}})

, below which the superfluid order parameter has the

{p}_{x}+i{p}_{y}

-wave symmetry. In the normal state near

{T}_{\mathrm{c}}^{{p}_{x}}, {p}_{x}

-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

{p}_{x}

direction. In the

{p}_{x}

-wave superfluid phase $({T}_{\mathrm{c}}^{{p}_{x}+i{p}_{y}}<T\ensuremath{\le}{T}_{\mathrm{c}}^{{p}_{x}})$, while the pseudogap in the

{p}_{x}

direction continuously changes to the superfluid gap, the pseudogap in the perpendicular direction to the

{p}_{x}

axis is found to continue developing because of enhanced

{p}_{y}

-wave and

{p}_{z}

-wave pairing fluctuations around the node of the

{p}_{x}

-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 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.