Eur. Phys. J. B 8, 47-56 (1999)
https://doi.org/10.1007/s100510050667

Optical study of an untwinned (Bi_1.57Pb_0.43)Sr₂CaCu₂O₈₊₈ single crystal: ab-plane anisotropy

¹ Department of Physics, University of Florida, Gainesville, FL 32611, USA
² Institut de Physique Appliquée, École Polytechnique Fédérale de Lausanne, PHB Ecublens, 1015 Lausanne, Switzerland

Received: 16 July 1998
Published online: 15 March 1999

Abstract

We report on the ab-plane polarized reflectance of an untwinned single crystal over the frequency range from 80 to (10 meV-4 eV) at temperatures between 10 and 300 K. We find a clear anisotropy in the ab-plane optical conductivity above and below T_c, which is very similar to that formerly published data of (M.A. Quijada et al., Z. Phys. B 94, 255 (1994)). We employ both the one-component and two-component analyses to the optical data, which suggest that the normal-state infrared anisotropy of originates not only from the mass anisotropy, but also from the scattering rate anisotropy. Our results provide evidence that the electronic structures within the plane are anisotropic. In the superconducting state, there is a definite ab-plane anisotropy to the far-infrared absorption. This anisotropy could be due either to anisotropy of the superconducting gap or to anisotropy of the mid-infrared component to the conductivity. We also observe the superconducting condensate is anisotropic: The value of the superconducting penetration depth in the a-direction is slightly smaller than that along the b-axis.