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Superlight small bipolarons

Hague, J. P.; Kornilovitch, P. E.; Samson, J. H. and Alexandrov, A. S. (2007). Superlight small bipolarons. Journal of Physics: Condensed Matter, 19(25), article no. 255214.

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DOI (Digital Object Identifier) Link: http://dx.doi.org/10.1088/0953-8984/19/25/255214
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Abstract

Recent angle-resolved photoemission spectroscopy (ARPES) has identified that a finite-range Fröhlich electron–phonon interaction (EPI) with c-axis polarized optical phonons is important in cuprate superconductors, in agreement with an earlier proposal by Alexandrov and Kornilovitch. The estimated unscreened EPI is so strong that it could easily transform doped holes into mobile lattice bipolarons in narrow-band Mott insulators such as cuprates. Applying a continuous-time quantum Monte Carlo algorithm (CTQMC), we compute the total energy, effective mass, pair radius, number of phonons and isotope exponent of lattice bipolarons in the region of parameters where any approximation might fail, taking into account the Coulomb repulsion and the finite-range EPI. The effects of modifying the interaction range and different lattice geometries are discussed with regards to analytical strong-coupling/non-adiabatic results. We demonstrate that bipolarons can be simultaneously small and light, provided suitable conditions on the electron–phonon and electron–electron interactions are satisfied. Such light small bipolarons are a necessary precursor to high-temperature Bose–Einstein condensation in solids. The light bipolaron mass is shown to be universal in systems made of triangular plaquettes, due to a novel crab-like motion. Another surprising result is that the triplet–singlet exchange energy is of the first order in the hopping integral and that triplet bipolarons are much heavier than singlets in certain lattice structures. Finally, we identify a range of lattices where superlight small bipolarons may be formed, and give estimates for their masses in the anti-adiabatic approximation.

Item Type: Journal Article
Copyright Holders: 2007 IOP Publishing Ltd
ISSN: 0953-8984
Project Funding Details:
Funded Project NameProject IDFunding Body
Not SetEP/C518365/1EPSRC
Not SetEP/D07777X/1EPSRC
Extra Information: 27 pp.
Academic Unit/Department: Science > Physical Sciences
Interdisciplinary Research Centre: Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)
Biomedical Research Network (BRN)
Item ID: 12291
Depositing User: James Hague
Date Deposited: 13 May 2009 14:47
Last Modified: 21 Mar 2014 14:06
URI: http://oro.open.ac.uk/id/eprint/12291
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