Bound states and superconductivity in dense Fermi systems
- PDF / 274,308 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 62 Downloads / 167 Views
ound States and Superconductivity in Dense Fermi Systems¶ D. Blaschkea, b and D. Zablockia, c a
Instytut Fizyki Teoretycznej, Uniwersytet Wroc l awski, 50-204 Wroc l aw, Poland Bogoliubov Laboratory for Theoretical Physics, JINR, 141980 Dubna, Russia c Institut für Physik der Universität, D-18051 Rostock, Germany Abstract—A quantum field theoretical approach to the thermodynamics of dense Fermi systems is developed for the description of the formation and dissolution of quantum condensates and bound states in dependence of temperature and density. As a model system, we study the chiral and superconducting phase transitions in twoflavor quark matter within the NJL model and their interrelation with the formation of quark–antiquark and diquark bound states. The phase diagram of quark matter is evaluated as a function of the diquark coupling strength and a coexistence region of chiral symmetry breaking, and color superconductivity is obtained at very strong coupling. The crossover between Bose–Einstein condensation (BEC) of diquark bound states and condensation of diquark resonances (Cooper pairs) in the continuum (BCS) is discussed as a Mott effect. This effect consists in the transition of bound states into the continuum of scattering states under the influence of compression and heating. We explain the physics of the Mott transition with special emphasis on the role of the Pauli principle for the case of the pion in quark matter. PACS numbers: 21.65.Qr, 11.10.St, 12.38.Lg DOI: 10.1134/S1063779608070071 b
1. INTRODUCTION Key issues of modern physics of dense matter are the concepts explaining the phenomena related to the appearance of quantum condensates in dense Fermi systems. Two regimes are well-known: the Bose–Einstein condensation (BEC) of bound states with an even number of Fermions and the condensation of bosonic correlations (e.g., Cooper pairs) in the continuum of unbound states according to the Bardeen–Cooper– Schrieffer (BCS) theory. While the former mechanism concerns states which are well-localized in coordinate space as they occur for strong enough attractive coupling, the latter mechanism applies to states which are correlated within a shell of the order of the energy gap Δ around the Fermi sphere in momentum space but delocalized in coordinate space. The transition between both regimes is called BEC–BCS crossover. Recently, this transition regime became accessible to laboratory experiments with ultracold gases of fermionic atoms coupled via Feshbach resonances with a strength tunable by applying external magnetic fields (see Fig. 1). After the preparation of fermionic dimers in 2003, now also the BEC [1, 2] and superfluidity of these dimers has been observed [3, 4]. The BEC–BCS crossover is physically related [5] to the bound state dissociation or Mott–Anderson delocalization transition [6] where the modification of the effective coupling strength is caused by electronic screening and/or Pauli blocking effects. It is thus a very general effect expected to occur ¶ The
text was submitted by the author
Data Loading...
