Spin Polaron-Bipolaron Scenario of Three Gap-Like Energy Scales in Superconducting Cuprates
P. Wróbela, A. Maciąga, W. Sulejaa, R. Ederb and R. Micnasc
aInstitute for Low Temperature and Structure Research, P.O. Box 1410, 50-950 Wrocław 2, Poland
bForschungszentrum Karlsruhe, Institut für Festkörphysik, P.O. Box 3640, D-76021 Karlsruhe, Germany
cFaculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań, Poland
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We argue that three gaps observed in underdoped cuprates can be attributed to the formation of antiferromagnetic spin polarons and bipolarons. Within the spin polaron scenario the antinodal pseudogap at he high energy scale originates from the change of the Fermi surface topology, induced by antiferromagnetic correlations. That change gives rise to the diminishing of the spectral weight at the antinodal region near the Brillouin zone boundary. We demonstrate that effect by analyzing effective models of doped antiferromagnets. The second type of pseudogap appearing at the intermediate energy scale originates from the phenomena which are precursory to superconductivity and predominantly concern the portion of the Fermi surface near the nodal region. In order to analyze the latter phenomenon we use the negative U Hubbard model, in which many details typical to spin polaron physics are neglected, but which contains the essential ingredient of it, that is the strong short range attraction. The lowest energy scale is related to the true superconducting gap which develops with doping, although both types of pseudogap diminish with doping. This behavior can be explained by the fact that the spin polaron band is empty in the undoped system and therefore the formation of the superconducting state in the system is forbidden. Due to a pedagogical character of this report, we present in the introduction a short overview of mostly recent experimental results which are related to the gap-pseudogap physics.
DOI: 10.12693/APhysPolA.118.292
PACS numbers: 74.20.Mn, 74.72.Kf