Relativistic description of BCS-BEC crossover in nuclear matter

Abstract

We study theoretically the di-neutron spatial correlations and the crossover from superfluidity of neutron Cooper pairs in the ${}^1{S}_0$ pairing channel to Bose-Einstein condensation (BEC) of di-neutron pairs for both symmetric and neutron matter in the microscopic relativistic pairing theory. We take the bare nucleon-nucleon interaction Bonn-B in the particle-particle channel and the effective interaction PK1 of the relativistic mean-field approach in the particle-hole channel. It is found that the spatial structure of neutron Cooper pair wave function evolves continuously from BCS-type to BEC-type as density decreases. We see a strong concentration of the probability density revealed for the neutron pairs in the fairly small relative distance around $1.5\mathrm{fm}$ and the neutron Fermi momentum $k_{Fn}\in [0.6,1.0]\mathrm{f}{\mathrm{m}}^{-1}$. However, from the effective chemical potential and the quasiparticle excitation spectrum, there is no evidence for the appearance of a true BEC state of neutron pairs at any density. The most BEC-like state may appear at $k_{Fn}\sim 0.2\mathrm{f}{\mathrm{m}}^{-1}$ by examining the density correlation function. From the coherence length and the probability distribution of neutron Cooper pairs as well as the ratio between the neutron pairing gap and the kinetic energy at the Fermi surface, some features of the BCS-BEC crossover are seen in the density regions, $0.05\mathrm{f}{\mathrm{m}}^{-1}<k_{Fn}<0.7(0.75)\mathrm{f}{\mathrm{m}}^{-1}$, for the symmetric nuclear (pure neutron) matter.

7 pages, 6 figures, Accepted by Physics Letters B

References in corpus (10)

• Relativistic Continuum Hartree Bogoliubov Theory for Ground State Properties of Exotic Nuclei
• Coexistence of BCS and BEC-like pair structures in halo nuclei
• Roles of the tensor and pairing correlations on the halo formation in 11Li
• BCS-BEC crossover of neutron pairs in symmetric and asymmetric nuclear matter
• Generic strong coupling behavior of Cooper pairs in the surface of superfluid nuclei
• Strong dineutron correlation in 8He and 18C
• Charge radius and dipole response of ${}^{11}$Li
• BCS-BEC Crossover and Thermodynamics in Asymmetric Nuclear Matter with Pairings in Isospin I=0 and I=1 Channels
• Correlation functions for a di-neutron condensate in asymmetric nuclear matter
• Pairing Properties of Symmetric Nuclear Matter in Relativistic Mean Field Theory

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• BCS-BEC crossovers and unconventional phases in dilute nuclear matter
• Phase diagram of dilute nuclear matter: Unconventional pairing and the BCS-BEC crossover
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• Nuclear systems under extreme conditions: isospin asymmetry and strong B-fields