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Title: Pairing and non-Fermi liquid behavior in partially flat-band systems: Beyond nesting physics

Journal Article · · Physical Review B
ORCiD logo [1];  [2];  [3];  [4];  [5];  [6]; ORCiD logo [7]
  1. Univ. of Tokyo (Japan); Univ. of Grenoble (France)
  2. Stanford Univ., CA (United States). Dept. of Physics; SLAC National Accelerator Lab., Menlo Park, CA (United States)
  3. Vienna Univ. of Technology (Austria)
  4. Pasargad Inst. for Advanced Innovative Solutions (PIAIS), Tehran (Iran); Washington Univ., St. Louis, MO (United States)
  5. Washington Univ., St. Louis, MO (United States)
  6. Stanford Univ., CA (United States). Dept. of Physics; Sharif Univ. of Technology, Tehran (Iran)
  7. National Inst. of Advanced Industrial Science and Technology (AIST), Tsukuba (Japan); Univ. of Tokyo (Japan)

While many-body effects in flat-band systems are receiving renewed hot interest in condensed-matter physics for superconducting and topological properties as well as for magnetism, studies have primarily been restricted to multiband systems (with coexisting flat and dispersive bands). Here we focus on one-band systems where a band is “partially flat,” comprising flat and dispersive portions in k space to reveal whether intriguing correlation effects can already arise on the simplest possible one-band level. For that, the two-dimensional repulsive Hubbard model is studied for two models having different flat areas in an intermediate-coupling regime with the dynamical mean-field theory combined with the fluctuation exchange approximation. We have a crossover from ferromagnetic to antiferromagnetic spin fluctuations as the band filling is varied and this triggers, for the model with a wider flat portion, a triplet-pair superconductivity favored over an unusually wide filling region, which is taken over by a sharply growing singlet pairing. For the model with a narrower flat portion, TC against filling exhibits an unusual double-peaked TC dome, associated with different numbers of nodes in the gap function having remarkably extended pairs in real space. We identify these as a manifestation of the physics outside the conventional nesting physics where only the pair scattering across the Fermi surface in designated (hot) spots is relevant. Another correlation effect arising from the flattened band is found in a non-Fermi-liquid behavior as detected in the momentum distribution function, frequency dependence of the self-energy, and spectral function. These indicate that unusual correlation physics can indeed occur in flat-band systems.

Research Organization:
SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC)
Grant/Contract Number:
AC02-76SF00515
OSTI ID:
1605016
Journal Information:
Physical Review B, Journal Name: Physical Review B Journal Issue: 1 Vol. 101; ISSN 2469-9950; ISSN PRBMDO
Publisher:
American Physical Society (APS)Copyright Statement
Country of Publication:
United States
Language:
English

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