Effects of Ni doping on the optical conductivity of YBa2Cu3O6.95

Christopher C. Homes; Q. Song; B. P. Clayman; D. A. Bonn; Ruixing Liang; Walter N. Hardy

doi:10.1117/12.241795

10 June 1996 Effects of Ni doping on the optical conductivity of YBa₂(Cu_1-xNi_x)₃O_6.95

Christopher C. Homes, Q. Song, B. P. Clayman, D. A. Bonn, Ruixing Liang, Walter N. Hardy

Proceedings Volume 2696, Spectroscopic Studies of Superconductors; (1996) https://doi.org/10.1117/12.241795
Event: Photonics West '96, 1996, San Jose, CA, United States

Abstract

The optical conductivity ((sigma) ₁) of twinned and untwinned single crystals of YBa₂(Cu_1-xNi_x)₃O_6.95 has been studied using infrared reflectance spectroscopy for x equals 0, 0.75 and 1.4% ('pure,' 'light' and 'heavily' doped). The optical properties have been calculated from a Kramers-Kronig analysis of the reflectance. Nickel acts as a point defect scatterer in the planes, but has only a small effect on T_c. (At the heaviest Ni doping, T_c is only suppressed by approximately equal to 4 K). In the pure, twinned samples for T very much less than T_c, there is a narrow, 'Drude'-like band at low frequency; the conductivity is observed to drop to a minimum of approximately equal to 1000 (Omega) ^-1 cm^-1 at approximately equal to 500 cm^-1 before gradually rising to join a temperature-independent midinfrared band. In the heavily- doped sample, there is a large amount of low-frequency residual conductivity; at 6 K some of the residual conductivity has been suppressed and a shoulder in (sigma) ₁ is visible at approximately equal to 300 cm^-1. In the lightly-doped sample, the approximately equal to 300 cm^-1 shoulder is visible already at 12 K. However, in the same detwinned sample, the shoulder in (sigma) ₁ is observed only for E (parallel) b, and is present in the normal state indicating that this feature is associated with the chains, and is not related to the superconductivity in these materials. The origin of this feature is discussed, and it is proposed that the shoulder at approximately equal to 300 cm^-1 may be related to the pseudogap observed along the c axis in the oxygen-underdoped materials.

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Christopher C. Homes, Q. Song, B. P. Clayman, D. A. Bonn, Ruixing Liang, and Walter N. Hardy "Effects of Ni doping on the optical conductivity of YBa₂(Cu_1-xNi_x)₃O_6.95", Proc. SPIE 2696, Spectroscopic Studies of Superconductors, (10 June 1996); https://doi.org/10.1117/12.241795

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