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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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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 Item
Copyright Holders: 2007 IOP Publishing Ltd
ISSN: 0953-8984
Project Funding Details:
Funded Project NameProject IDFunding Body
Not SetEP/C518365/1EPSRC (Engineering and Physical Sciences Research Council)
Not SetEP/D07777X/1EPSRC (Engineering and Physical Sciences Research Council)
Extra Information: 27 pp.
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Physical Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Research Group: Physics
Item ID: 12291
Depositing User: James Hague
Date Deposited: 13 May 2009 14:47
Last Modified: 10 Dec 2018 18:45
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