Tunneling and fluctuating electron-hole Cooper pairs in double bilayer graphene

Dmitry K. Efimkin, G. William Burg, Emanuel Tutuc, and Allan H. MacDonald
Phys. Rev. B 101, 035413 – Published 15 January 2020

Abstract

A strong low-temperature enhancement of the tunneling conductance between graphene bilayers has been reported recently and interpreted as a signature of equilibrium electron-hole pairing, first predicted in bilayers more than 40 years ago but previously unobserved. Here we provide a detailed theory of conductance enhanced by fluctuating electron-hole Cooper pairs, which are a precursor to equilibrium pairing, that accounts for specific details of the multiband double graphene bilayer system which supports several different pairing channels. Above the equilibrium condensation temperature, pairs have finite temporal coherence and do not support dissipationless tunneling. Instead they strongly boost the tunneling conductivity via a fluctuational internal Josephson effect. Our theory makes predictions for the dependence of the zero bias peak in the differential tunneling conductance on temperature and electron-hole density imbalance that capture important aspects of the experimental observations. In our interpretation of the observations, cleaner samples with longer disorder scattering times would condense at temperatures Tc up to 50K, compared to the record Tc1.5K achieved to date in experiment.

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  • Received 18 March 2019
  • Revised 7 June 2019

DOI:https://doi.org/10.1103/PhysRevB.101.035413

©2020 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Dmitry K. Efimkin*

  • Center for Complex Quantum Systems, University of Texas at Austin, Austin, Texas 78712-1192, USA and School of Physics and Astronomy and ARC Centre of Excellence in Future Low-Energy Electronics Technologies, Monash University, Victoria 3800, Australia

G. William Burg and Emanuel Tutuc

  • Microelectronics Research Center, Department of Electrical and Computer Engineering, University of Texas at Austin, Austin, Texas 78758, USA

Allan H. MacDonald

  • Center for Complex Quantum Systems, University of Texas at Austin, Austin, Texas 78712-1192, USA

  • *dmitry.efimkin@monash.edu

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Issue

Vol. 101, Iss. 3 — 15 January 2020

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