Two-Copper-Atom Units Induce a Pseudo Jahn–Teller Polaron in Hole-Doped Cuprate Superconductors

Multiconfiguration molecular orbital cluster calculation results combined with experimental observations suggest that the local electronic state unit for a doped hole contains at least two Cu atoms in contrast to the Zhang–Rice singlet state that includes only one Cu atom. The cluster calculation shows that a doped hole in a two copper containing cluster induces a pseudo Jahn–Teller instability with stabilization energy that agrees with a peak in the photoinduced conductivity measurement, and the Cu–O bond length fluctuations that explain the EXAFS experiment; the charge-transfer energy gap observed in the optical conductivity measurement, and an excitation energy that corresponds to a peak in the energy loss function are also obtained from the calculation including two Cu atoms.

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