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SUMMARY:Calculation of the critical temperature for Fermi superfluid throu
ghout the BCS-BEC crossover.
DTSTART;VALUE=DATE-TIME:20171123T133000Z
DTEND;VALUE=DATE-TIME:20171123T160000Z
DTSTAMP;VALUE=DATE-TIME:20200602T190430Z
UID:indico-event-14354@agenda.infn.it
DESCRIPTION:\n\nThe problem of the theoretical description of the critical
temperature Tc of a Fermi superfluid dates back to the work of Gor'kov an
d Melik-Barkhudarov (GMB)\, who addressed it for a weakly-coupled (dilute)
superfluid in what would today be referred to as the (extreme) BCS (weak-
coupling) limit of the BCS-BEC crossover. The point made in this context b
y GMB was that particle-particle (pairing) excitations\, which are respons
ible for superfluidity to occur below Tc\, and particle-hole excitations\,
which give rise to screening also in a normal system\, get e ectively dis
entangled from each other in the BCS limit\, thus yielding a reduction by
a factor 2:2 of the value of Tc obtained when neglecting screening e ects.
Subsequent work on this topic\, that was aimed at extending the original
GMB argument away from the BCS limit\, has tout court kept this disentangl
ing between pairing and screening throughout the BCS-BEC crossover\, witho
ut realising that the conditions for it to be valid are soon violated away
from the BCS limit. Here\, we reconsider this problem from a more general
perspective and argue that pairing and screening are intrinsically entang
led with each other along the whole BCS-BEC crossover but for the BCS limi
t considered by GMB\, with the particle-hole excitations soon transmuting
into particle-particle excitations away from this limit. We substantiate o
ur argument by performing a detailed numerical calculation of the GMB diag
rammatic contribution suitably extended to the whole BCS-BEC crossover\, w
here the full wave-vector and frequency dependence occurring in the repeat
ed two-particle in medium scattering is duly taken into account. Our numer
ical calculations are tested against analytic results available in both th
e BCS and BEC limits\, and the contribution of the GMB approach to the sca
ttering length of composite bosons in the BEC limit is highlighted. We cal
culate Tc throughout the BCS-BEC crossover and find that it agrees quite w
ell with available Monte Carlo calculations in the unitarity regime.\n\n\n
\n\n\n\n\nhttps://agenda.infn.it/event/14354/
LOCATION:LNF INFN Aula Seminari
URL:https://agenda.infn.it/event/14354/
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