Superconductivity in repulsively interacting fermions on a diamond chain: Flat-band-induced pairing

Keita Kobayashi, Masahiko Okumura, Susumu Yamada, Masahiko Machida, and Hideo Aoki
Phys. Rev. B 94, 214501 – Published 1 December 2016

Abstract

To explore whether a flat-band system can accommodate superconductivity, we consider repulsively interacting fermions on the diamond chain, a simplest possible quasi-one-dimensional system that contains a flat band. Exact diagonalization and the density-matrix renormalization group are used to show that we have a significant binding energy of a Cooper pair with a long-tailed pair-pair correlation in real space when the total band filling is slightly below 1/3, where a filled dispersive band interacts with the flat band that is empty but close to EF. Pairs selectively formed across the outer sites of the diamond chain are responsible for the pairing correlation. At exactly 1/3-filling an insulating phase emerges, where the entanglement spectrum indicates the particles on the outer sites are highly entangled and topological. These come from a peculiarity of the flat band in which “Wannier orbits” are not orthogonalizable.

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  • Received 12 August 2016
  • Revised 23 October 2016

DOI:https://doi.org/10.1103/PhysRevB.94.214501

©2016 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Keita Kobayashi1, Masahiko Okumura1, Susumu Yamada1,2, Masahiko Machida1, and Hideo Aoki3,4

  • 1CCSE, Japan Atomic Energy Agency, Kashiwa, Chiba 277-0871, Japan
  • 2Computational Materials Science Research Team, RIKEN AICS, Kobe, Hyogo 650-0047, Japan
  • 3Department of Physics, University of Tokyo, Hongo, Tokyo 113-0033, Japan
  • 4Electronics and Photonics Research Institute, Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan

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Issue

Vol. 94, Iss. 21 — 1 December 2016

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