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On the electron pairing mechanism of copper-oxide high temperature superconductivity

Cornell Affiliated Author(s)


S.M. O’Mahony
W. Ren
W. Chen
Y.X. Chong
X. Liu
H. Eisaki
S. Uchida
M.H. Hamidian
J.C.S. Davis


The elementary CuO2 plane sustaining cuprate high-temperature superconductivity occurs typically at the base of a periodic array of edge-sharing CuO5 pyramids. Virtual transitions of electrons between adjacent planar Cu and O atoms, occurring at a rate t/̄h and across the charge-transfer energy gap ℇ, generate “superexchange†spin–spin interactions of energy J ≈ 4t4=ℇ3 in an antiferromagnetic correlated-insulator state. However, hole doping this CuO2 plane converts this into a very-high-temperature superconducting state whose electron pairing is exceptional. A leading proposal for the mechanism of this intense electron pairing is that, while hole doping destroys magnetic order, it preserves pair-forming superexchange interactions governed by the charge-transfer energy scale ℇ. To explore this hypothesis directly at atomic scale, we combine single-electron and electron-pair (Josephson) scanning tunneling microscopy to visualize the interplay of ℇ and the electron-pair density nP in Bi2Sr2CaCu2O8+x. The responses of both ℇ and nP to alterations in the distance δ between planar Cu and apical O atoms are then determined. These data reveal the empirical crux of strongly correlated superconductivity in CuO2, the response of the electron-pair condensate to varying the charge-transfer energy. Concurrence of predictions from strong-correlation theory for hole-doped charge-transfer insulators with these observations indicates that charge-transfer superexchange is the electron-pairing mechanism of superconductive Bi2Sr2CaCu2O8+x. © 2022 the Author(s). Published by PNAS.

Date Published


Proceedings of the National Academy of Sciences of the United States of America








Group (Lab)

J.C. Seamus Davis Group

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