Large-shift Raman scattering in insulating cuprate materials

This thesis describes the use of large-shift ordinary Raman techniques to probe features near the charge-transfer gap in insulating cuprate materials, including the T' phase materials (R2Cu04, R=Gd, Eu, Sm, Nd, Pr), T phase La2Cu04, and 123 phase PrBa2Cu3Cu06 and YBa2Cu3Cu06+x· For all of these materials, several features are observed near 12000 cm-1 (-1.5 eV) with A2g, B1g, and A1g symmetry. At low temperatures, the largest feature with A2g symmetry splits in all the insulating cuprates into three distinct peaks: a strong main peak, and two weaker side-bands offset approximately 600 and 1500 cm-1 higher in energy respectively. A B1g feature coinciding in position with the optical conductivity peak is observed in all the T' phase materials, but not in the other insulators. An A1g peak is observed in Gd2Cu04 and Eu2Cu04 40-50 cm-1 lower in energy than the main A2g peak, and in YBa2Cu3Cu06 around 2400 cm-1 above the main A2g peak. All of these features have unusual, temperature-dependent resonance behavior with the incident photon energy, and they seem to weaken in YBa2Cu3Cu06+x as x moves through the metal-insulator transition. Some residual A2g scattering may remain in superconducting phases. We propose an explanation for many of the above observations involving a copper d xy to d x2_Y2 orbital transitions. In this picture, the main A2g peak is the d-d transition energy, the first side-band results from coupled phonon scattering, and the second sideband results from unusual coupled two-magnon scattering.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Year dc:date

2012

Author dc:creator

• Salamon, David Vigdor

Contributors dc:contributor

• Klein, Miles V.

• raman scattering
• cuprate materials

Statement dc:rights

• ©1994 Salamon

Language dc:language

en

Identifier

3779838

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/29974