Large-shift Raman scattering features in superconducting YBa2Cu3O6+x

Abstract

We apply the large-shift Raman-scattering technique to explore the metal-insulator transition in YBa2Cu3O6+x. In a doping-dependence study for x∼0 to 1, we find that the previously observed A2g scattering features near 1.5 eV split in energy as doping is increased and have increasingly mixed A1g+A2g symmetry. At the same time, the overall A2g Raman intensity decreases. We use an annealing/quenching technique on a x∼0.4 sample to explore the transition region further, and find that the Raman intensity increases just after quenching but the peaks do not shift in energy. Room-temperature annealing of the quenched sample shows an initial drop in A2g peak intensity over 100 min, a plateau level from 100 to 500 min, and a final slow drop to the original intensity level from 500 to 1100 min. We see the suppressions of A2g Raman intensity from doping and annealing as resulting from increases in the carrier concentration. Peak splitting and mixed-symmetry effects seem to be more closely related to variations in the lattice parameters, probably as a result of changes to the in-plane copper d orbitals. © 1996 The American Physical Society.

Source-reported materials — not catalogue approval

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