SUPERFLUID STATES OF NUCLEAR MATTER BEYOND THE BCS APPROXIMATION

The recent progress in the pairing problem and the superfluidity of neutron stars is reviewed. The theory of superfluidity in nuclear and neutron matter is developed beyond the BCS approximation. In particular, the dispersion effects including the depletion of the Fermi surface and the core polarization are discussed within the Brueckner theory. In addition, the effects of vertex correction to the pairing interaction, based on RPA, are incorporated in the generalized gap equation. The isospin singlet (neutron–proton) pairing is investigated in connection with the low-density crossover from a superfluid Fermi system to a Bose–Einstein condensate and the isospin suppression of pairing in neutron-rich matter. The onset of different superfluid states of neutron–neutron and proton–proton pairing in neutron stars is discussed in the context of application to rotational motion and cooling process.

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Josephson dynamics of strongly interacting superfluid Fermi gases in double-well potentials

International Journal of Modern Physics B ◽

10.1142/s0217979221500028 ◽

2020 ◽

pp. 2150002

Author(s):

Ji Li ◽

Wen Wen ◽

Yuke Zhang ◽

Xiaodong Ma

Keyword(s):

Einstein Condensate ◽

Interaction Terms ◽

Bose Einstein Condensate ◽

Strongly Interacting ◽

Fermi Superfluids ◽

The Cross ◽

Bose Einstein ◽

Double Well Potential ◽

Zero Phase ◽

Superfluid Fermi

In this work, we study the nonlinear Josephson dynamics of Fermi superfluids in the crossover from Bardeen–Cooper–Schrieffer (BCS) superfluid to a molecular Bose-Einstein condensate (BEC) in a double-well potential. Under a two-mode approximation, we derive a full two-mode (fTM) model including all interaction energy terms. By solving the fTM model numerically, we study the zero-phase and [Formula: see text]-phase modes of Josephson oscillations in the BCS–BEC crossover. We find that in the strongly interacting regime the cross interaction terms not appearing in the two-mode model cannot be easily ignored. The cross interactions can alter the behaviors of Josephson dynamics substantially, and interestingly the alterations for the zero-phase and [Formula: see text]-phase modes are just opposite.

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EVOLUTION OF INTERFERENCE PATTERNS OF SUPERFLUID FERMI GASES RELEASED FROM A TWO-DIMENSIONAL OPTICAL LATTICE

International Journal of Modern Physics B ◽

10.1142/s0217979212500178 ◽

2012 ◽

Vol 26 (03) ◽

pp. 1250017

Author(s):

SUJUAN LIU ◽

WEN WEN ◽

GUOXIANG HUANG

Keyword(s):

Interference Pattern ◽

Optical Lattice ◽

Initial Distribution ◽

Einstein Condensate ◽

Main Peak ◽

Two Dimensional ◽

Bose Einstein Condensate ◽

Propagator Method ◽

Bose Einstein ◽

Superfluid Fermi

We study interference patterns and their time evolution of a superfluid fermionic gas released from a two-dimensional (2D) optical lattice below and above Feshbach resonance. We calculate initial distribution of many subcondensates formed in a combined potential of a parabolic trap and a 2D optical lattice in the crossover from Bardeen–Cooper–Schrieffer (BCS) superfluid to a Bose–Einstein condensate (BEC). By using Feynman propagator method combined with numerical simulations we investigate the interference patterns of the subcondensates for two different cases. One is when both the parabolic trap and optical lattice are switched off. In this case, interference pattern displays a main peak and many secondary peaks. The distance between these interference peaks grows as time increases. The other one is when only the 2D optical lattice is switched off. The interference pattern in this case is found to display decay and revival, and such behavior repeats periodically with increasing time. In different regimes of the BCS-BEC crossover, coherent arrays of interference patterns show different features, which can be used to characterize experimentally different properties in different superfluid regimes of the BCS–BEC crossover.

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COLLAPSING NEUTRON STARS DRIVEN BY CRITICAL MAGNETIC FIELDS AND EXPLODING BOSE–EINSTEIN CONDENSATES

International Journal of Modern Physics D ◽

10.1142/s0218271805007516 ◽

2005 ◽

Vol 14 (11) ◽

pp. 1855-1860 ◽

Cited By ~ 4

Author(s):

H. PÉREZ ROJAS ◽

A. PÉREZ MARTÍNEZ ◽

HERMAN J. MOSQUERA CUESTA

Keyword(s):

Magnetic Fields ◽

Neutron Stars ◽

Vector Boson ◽

Einstein Condensate ◽

Relativistic Limit ◽

Bose Einstein Condensate ◽

Critical Magnetic Fields ◽

Neutral Vector ◽

Bose Einstein ◽

The Magnetic Field

A Bose–Einstein condensate of a neutral vector boson bearing an anomalous magnetic moment is suggested as a model for ferromagnetic origin of magnetic fields in neutron stars. The vector particles are assumed to arise from parallel spin-paired neutrons. A negative pressure perpendicular to the external field B is acting on this condensate, which for large densities, compress the system, and may produce a collapse. An upper bound of the magnetic fields observable in neutron stars is given. In the the non-relativistic limit, the analogy with the behavior of exploding Bose–Einstein condensates (BECs) for critical values of the magnetic field is briefly discussed.

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Super Efimovian expansions of superfluid Fermi gases in the BCS–BEC crossover

International Journal of Modern Physics B ◽

10.1142/s0217979218502302 ◽

2018 ◽

Vol 32 (21) ◽

pp. 1850230 ◽

Cited By ~ 2

Author(s):

Liang Zhang ◽

Wen Wen ◽

XiaoDong Ma ◽

Ying Wang

Keyword(s):

Einstein Condensate ◽

Fermi Gases ◽

Unitary Limit ◽

Hydrodynamic Equations ◽

Axially Symmetric ◽

Fermi Superfluid ◽

Bose Einstein Condensate ◽

Large Anisotropy ◽

Bose Einstein ◽

Superfluid Fermi

We study the super Efimovian expansions of a superfluid Fermi gas in the crossover from Bardeen–Cooper–Schrieffer (BCS) superfluid to a Bose–Einstein condensate (BEC), by using superfluid hydrodynamic equations with the equation of state fitting from the experimental data and a scaling approach. We find that in an isotropic trap, the super Efimovian expansion of the Fermi superfluid in the unitary limit is characterized by the double-log periodicity, while for an axially symmetric trap, the double-log periodicity only emerges in the longer direction for a large anisotropy of the trapping frequencies. Away from unitarity where the scale invariance is broken, the super Efimovian expansions of the superfluid Fermi gases deviate from the double-log oscillations. The oscillations in the BCS regime deviate upward from the double-log oscillations, whereas the oscillations in the BEC regime deviate downward and the deviation in the BEC limit is the most significant. This difference can be used to discriminate different superfluid regimes.

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FERMION CONDENSATION IN A RELATIVISTIC DEGENERATE STAR: ARRESTED COLLAPSE AND MACROSCOPIC EQUILIBRIUM

International Journal of Modern Physics D ◽

10.1142/s0218271806009522 ◽

2006 ◽

Vol 15 (12) ◽

pp. 2257-2265

Author(s):

M. P. SILVERMAN

Keyword(s):

Neutron Stars ◽

Scattering Length ◽

Einstein Condensate ◽

Atomic Gases ◽

Spherically Symmetric ◽

Cooper Pairing ◽

Bose Einstein Condensate ◽

Composite Bosons ◽

Degeneracy Pressure ◽

Bose Einstein

Fermionic Cooper pairing leading to the BCS-type hadronic superfluidity is believed to account for periodic variations ("glitches") and subsequent slow relaxation in spin rates of neutron stars. Under appropriate conditions, however, fermions can also form a Bose–Einstein condensate of composite bosons. Both types of behavior have recently been observed in tabletop experiments with ultra-cold fermionic atomic gases. Since the behavior is universal (i.e., independent of atomic potential) when the modulus of the scattering length greatly exceeds the separation between particles, one can expect analogous processes to occur within the supradense matter of neutron stars. In this paper, I show how neutron condensation to a Bose–Einstein condensate, in conjunction with relativistically exact expressions for fermion energy and degeneracy pressure and the relations for thermodynamic equilibrium in a spherically symmetric space–time with Schwarzschild metric, leads to stable macroscopic equilibrium states of stars of finite density, irrespective of mass.

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