Correlation functions for a di-neutron condensate in asymmetric nuclear matter

Abstract

Recent calculations with an effective isospin dependent contact interaction show the possibility of the crossover from superfluidity of neutron Cooper pairs in ${}^1{S}_0$ pairing channel to Bose-Einstein condensation (BEC) of di-neutron bound states in dilute nuclear matter. The density and spin correlation functions are calculated for a di-neutron condensate in asymmetric nuclear matter with the aim to find the possible features of the BCS-BEC crossover. It is shown that the zero-momentum transfer spin correlation function satisfies the sum rule at zero temperature. In symmetric nuclear matter, the density correlation function changes sign at low momentum transfer across the BCS-BEC transition and this feature can be considered as a signature of the crossover. At finite isospin asymmetry, this criterion gives too large value for the critical asymmetry ${\alpha }_c^d\sim 0.9$, at which the BEC state is quenched. Therefore, it can be trusted for the description of the density-driven BCS-BEC crossover of neutron pairs only at small isospin asymmetry. This result generalizes the conclusion of the study in Phys. Rev. Lett. {\bf 95}, 090402 (2005), where the change of sign of the density correlation function at low momentum transfer in two-component quantum fermionic atomic gas with the balanced populations of fermions of different species was considered as an unambiguous signature of the BCS-BEC transition.

Prepared with RevTeX4, 8pp., 7 figs., 1 table; v2: extended discussion; version accepted in PRC

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• Phase diagram of dilute nuclear matter: Unconventional pairing and the BCS-BEC crossover
• BCS-BEC Crossover in Symmetric Nuclear Matter at Finite Temperature: Pairing Fluctuation and Pseudogap
• BCS-BEC Crossover and Thermodynamics in Asymmetric Nuclear Matter with Pairings in Isospin I=0 and I=1 Channels
• BCS-BEC crossover in nuclear matter with the relativistic Hartree-Bogoliubov theory
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• Dineutron correlations and BCS-BEC crossover in nuclear matter with the Gogny pairing force
• Two-neutron correlations in microscopic wave functions of He-6, He-8 and C-12
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