title: Condensed fraction of an atomic Bose gas induced by critical correlations.
abstract: We study the condensed fraction of a harmonically trapped atomic Bose gas at the critical point predicted by mean-field theory. The nonzero condensed fraction f(0) is induced by critical correlations which increase the transition temperature T(c) above T(c) (MF). Unlike the T(c) shift in a trapped gas, f(0) is sensitive only to the critical behavior in the quasiuniform part of the cloud near the trap center. To leading order in the interaction parameter a/λ(0), where a is the s-wave scattering length and λ(0) the thermal wavelength, we expect a universal scaling f(0) proportionally (a/λ(0))(4). We experimentally verify this scaling using a Feshbach resonance to tune a/λ(0). Further, using the local density approximation, we compare our measurements with the universal result obtained from Monte Carlo simulations for a uniform system, and find excellent quantitative agreement.
authors.affiliation: Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
authors.forename: Robert P
authors.initials: RP
authors.lastname: Smith
authors.forename: Naaman
authors.initials: N
authors.lastname: Tammuz
authors.forename: Robert L D
authors.initials: RL
authors.lastname: Campbell
authors.forename: Markus
authors.initials: M
authors.lastname: Holzmann
authors.forename: Zoran
authors.initials: Z
authors.lastname: Hadzibabic