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Negative-U extended Hubbard model for doped barium bismuthates

Taraphder, A and Krishnamurthy, HR and Pandit, Rahul and Ramakrishnan, TV (1995) Negative-U extended Hubbard model for doped barium bismuthates. In: Physical Review B, 52 (2). 1368 -1388.


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We present detailed mean-field and random-phase-approximation studies of the negative-U, extended Hubbard model with a view to understanding the properties of the doped barium bismuthates. In particular, we obtain the phase diagram, the excitation spectrum, and the optical conductivity in the semiconducting phase of the bismuthates. We show by explicit calculations how this model leads to a natural explanation for the two, well-separated transport and optical gaps observed in the semiconducting phases of the bismuthates. We fix the parameters in our model by fitting these experimentally observed gaps; and with these parameter values we compute other properties of these systems. We also show how metallic screening and disorder can decrease the superconducting Tc dramatically. Our theory leads to an exotic charge-transport mechanism, dominated by charge ±2e bosons (cooperons), in the semiconducting phases of these systems.

Item Type: Journal Article
Publication: Physical Review B
Publisher: American Physical Society
Additional Information: Copyright for this article belongs to American Physical Society
Department/Centre: Division of Physical & Mathematical Sciences > Physics
Date Deposited: 27 Jul 2004
Last Modified: 19 Sep 2010 04:14
URI: http://eprints.iisc.ac.in/id/eprint/1166

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