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Title: Superconductor-insulator transition and Fermi-Bose crossovers

The direct transition from an insulator to a superconductor (SC) in Fermi systems is a problem of long-standing interest, which necessarily goes beyond the standard BCS paradigm of superconductivity as a Fermi surface instability. We introduce here a simple, translationally invariant lattice fermion model that undergoes a SC-insulator transition (SIT) and elucidate its properties using analytical methods and quantum Monte Carlo simulations. We show that there is a fermionic band insulator to bosonic insulator crossover in the insulating phase and a BCS-to-BEC crossover in the SC. The SIT is always found to be from a bosonic insulator to a BEC-like SC, with an energy gap for fermions that remains finite across the SIT. Hence, the energy scales that go critical at the SIT are the gap to pair excitations in the insulator and the superfluid stiffness in the SC. In addition to giving insight into important questions about the SIT in solid-state systems, our model should be experimentally realizable using ultracold fermions in optical lattices.
 [1] ;  [2] ;  [2] ;  [3] ;  [3]
  1. Univ. of North Dakota, Grand Forks, ND (United States). Dept. of Physics and Astrophysics
  2. Ohio State Univ., Columbus, OH (United States). Dept. of Physics
  3. Univ. of California, Davis, CA (United States). Dept. of Physics
Publication Date:
OSTI Identifier:
Grant/Contract Number:
FG02-07ER46423; AC52-07NA27344; 15-ERD-013
Published Article
Journal Name:
Physical Review. X
Additional Journal Information:
Journal Volume: 6; Journal Issue: 2; Journal ID: ISSN 2160-3308
American Physical Society
Research Org:
The Ohio State Univ., Columbus, OH (United States)
Sponsoring Org:
USDOE; National Science Foundation (NSF); UC Office of the President
Country of Publication:
United States
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; quantum monte-carlo; hubbard-model; einstein condensation; ultracold atoms; mott insulator; lattice; physics; superfluid; excitons; systems