ISSN:
1572-9605
Keywords:
pairing interaction
;
cuprates
;
phonon mechanism
Source:
Springer Online Journal Archives 1860-2000
Topics:
Electrical Engineering, Measurement and Control Technology
,
Physics
Notes:
Abstract Thermal difference reflectance (TDR) spectra taken on a large number of superconducting cuprates has enabled us to determine the energy dependence and strength of the pairing interaction in each. All show strong contributions from the phonons and a smaller, but significant contribution from an electronic transition near 1.7 eV. Recent improvements in the signal-to-noise ratio have revealed that the electronic excitation is accompanied in all cases by a weaker companion about 0.5 eV lower in energy. No other contributions are found. We identify these transitions as the d z2 to d x2–y2 excitations of the Cu ion in the 3d 9 and 3d 8 states, respectively, and have calculated the coupling strength mediated by each. The calculated values agree in order of magnitude with the observed strengths. We find that, in addition to the direct electronic coupling that corresponds to an electron–phonon-like term, the overlap between the oxygen and the copper orbitals leads to an exchange term. The direct term couples only to an s-wave gap, as for phonons, while the exchange term couples s-wave to d-wave, and vice versa. We discuss the consequences of this result.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1007893526924
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