title: Density and spin response functions in ultracold fermionic atom gases.
abstract: We propose a new method of detecting the onset of superfluidity in a two-component ultracold fermionic gas of atoms governed by an attractive short-range interaction. By studying the two-body correlation functions we find that a measurement of the momentum distribution of the density and spin-response functions allows one to access separately the normal and anomalous densities. The change in sign at low momentum transfer of the normal-ordered part of the density response function signals the transition between a BEC and a BCS regime, characterized by small and large pairs, respectively. This change in sign of the density response function represents an unambiguous signature of the BEC-to-BCS crossover. Spin rotational symmetry breaking due to the magnetic field, if observed, can be used to validate the one-channel model.
authors.affiliation: Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
authors.forename: Bogdan
authors.initials: B
authors.lastname: Mihaila
authors.forename: Sergio
authors.initials: S
authors.lastname: Gaudio
authors.forename: Krastan B
authors.initials: KB
authors.lastname: Blagoev
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Balatsky
authors.forename: Peter B
authors.initials: PB
authors.lastname: Littlewood
authors.forename: Darryl L
authors.initials: DL
authors.lastname: Smith