2014/09/30 by Madhuparna Karmakar, Pinaki Majumdar
Physics and Astronomy · #Advanced Condensed Matter Physics #BCS theory #Cold Atom Physics and Bose-Einstein Condensates #Condensed matter physics #Fermion #Gapless playback #Hubbard model #Lattice (music) #Momentum (technical analysis) #Optical lattice #Pairing #Physics #Physics of Superconductivity and Magnetism #Population #Quantum mechanics #Superconductivity #Superfluidity #cond-mat.quant-gas #cond-mat.str-el #cond-mat.supr-con
paper · pdf · doi:10.1103/physreva.93.053609
published as Phys. Rev. A 93, 053609 (2016) · 10 pages, 10 figures. This version and arXiv:1508.00393 are published as a combined text
openalex publication_date 2016/05/10 · arxiv created 2016/05/25 · arxiv updated 2016/05/26 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We study s-wave superconductivity in the two-dimensional attractive Hubbard model in an applied magnetic field, assume the extreme Pauli limit, and examine the role of spatial fluctuations in the coupling regime corresponding to BCS-BEC crossover. We use a decomposition of the interaction in terms of an auxiliary pairing field, retain the static mode, and sample the pairing field via a Monte Carlo approach. The method requires iterative solution of the Bogoliubov--de-Gennes equations for amplitude- and phase-fluctuating configurations of the pairing field. We establish the full thermal phase diagram of this strong-coupling problem. At low field we observe the magnetized but homogeneous ``breached pair'' superfluid phase. It reveals that Tc scales an order of magnitude below the mean-field estimate, spontaneous inhomogeneity in the field-induced magnetization, and a strong nonmonotonicity in the temperature dependence of the low-energy density of states. We compare our results to the experimental phase diagram of the imbalanced Fermi gas at unitarity. At higher field we obtain the modulated Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phases. The thermal transition from the FFLO phases to the normal state is strongly first order. We track the fermionic momentum distribution, the density of states, and the pairing structure factor deep into the normal state. The pairing structure factor retains weak signature of finite momentum pairing to a high temperature despite the low Tc itself, while the spin-resolved density of states changes from the ``pseudogapped'' FFLO character to gapless and pseudogapped again with increasing temperature.