BCS–BEC crossover in cold atomic and in nuclear systems

Low-dimensional fluctuations and pseudogap in Gaudin-Yang Fermi gases

“…In this paper, we elucidate pairing fluctuation effects in 1D Gaudin-Yang Fermi gas at finite temperature within the diagrammatic approach, which has successfully been applied to higher-dimensional systems [6,9,11,12,14]. Our numerical results of the number density show an excellent agreement with the recent QMC results [66].…”

“…3(c2) since the low-energy pole in (q, iν ) becomes close to q = 0 and gives a strong particle-hole coupling, one can clearly see the pseudogap accompanying with particlehole branches. Intuitively, this pseudogap structure can be understood from the so-called static approximation where [12,14]. Here, 2 pg = −T q,iν (q, iν ) is called the pseudogap parameter which characterizes its size in A(p, ω) as well as ρ(ω).…”

“…The pseudogapped dispersion of fermions yields that the elementary excitation is now replaced by the bosonic two-particle excitations [94]. We note that, in this paper, we do not specify the crossover boundary between the pseudogap regime and the bound molecular regime since its definition involves ambiguity [11,12,14]. We also compare the dispersion ξ eff p,σ obtained from the imaginary-time Green's function G σ (p, τ ) as…”

“…A pseudogap phenomenon, which is the suppression of the density of states (DOS) around a Fermi level, has been a central issue in strongly correlated quantum many-body systems such as high-T c superconductors [1][2][3][4][5], ultracold atoms [6][7][8][9][10][11][12][13][14], and nuclear and quark matter [15][16][17][18][19][20]. Although the origin of the pseudogap strongly depends on the properties of each system, it is believed that the pseudogap is induced by fluctuation effects dominating nontrivial characters of the systems.…”

Hidden Pseudogap and Excitation Spectra in a Strongly Coupled Two-Band Superfluid/Superconductor

“…One of the exciting topics in the two-band BCS-BEC crossover is the existence of pseudogaps in the single-particle excitation in the normal state (for reviews discussing the pseudogap, see [27][28][29]). While several experiments for FeSe report signals of pseudogaps and preformed Cooper pairs [30][31][32][33], a recent scanning tunneling spectroscopy (STS) measurement did not observe a pseudogap behavior even in the crossover regime of the BCS-BEC crossover [34].…”