D. H. Rapkine

Variations in the far-infrared reflectivity of Ba2YCu3Ox

We present an empirical summary of the far-infrared reflectivity of 18 samples of Ba2YCu3Ox, with emphasis on 10 microtwinned crystals with x nominally near 7. The results vary among samples, indicating that further oriented, necessary to identify the intrinsic behavior to our satisfaction. At this stage the general behavior allows work will be a constant relaxation rate for charge carriers and to make only general remarks concerning the us to rule out superconducting energy gap.

Scaling of an infrared absorption with Tc in a cuprate superconductor

We have studied the complex optical conductivity of Ba 2 YCu 3 O 6+x crystals for 0 c in two related respects: 1) its spectral weight increases, and 2) it shifts to lower frequency.

Properties of optical features in YBa 2 Cu 3 O 7 − δ

Characteristic optical features in the far-infrared conductivity of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} crystals have been studied as a function of doping. We focus particularly on a reflectivity edge near 435 cm{sup {minus}1} which we find to be both insensitive to carrier concentration (i.e., {ital T}{sub {ital c}}), and present in the normal state of some samples. These results place tight constraints on possible interpretations of this feature.

THE ENERGY GAP AND TWO-COMPONENT ABSORPTION IN A HIGH Tc SUPERCONDUCTOR

ABSTRACT Evidence is discussed favoring an energy gap of conventional size and a frequency dependent conductivity with two components.

Cu-0 Superconductors: Through a Lens, but Darkly

The shock of superconducting transition temperatures (Tc’s) greater than 25 K in Cu-O based compounds1 has loosed a tidal wave of research. We have involved ourselves in a study of the optical properties of these materials, with particular emphasis on La2-xSrxCuO4 compounds. Recently we reported 2 reflectivity, R, spectra of La2-xSrxCuO4 for x = 0 and 0.175, and of Ba2YCu3O9-δ (δ~2.1) over a broad range of photon energy. The most striking observation was the profound deviation from the expected Drude-like R in the metallic compounds. Fitting R required that ∈ (ω) be dominated by a transition at energy 0.45 eV in La1.825Sr175CuO4 and 0.65 eV in Ba2YCu3O9-δ. From our fit we determined that the integrated oscillator strength in the 0.45 eV feature in La1.825Sr0.175CuO4 corresponded to a value of Neff m/m* of 2.5xl021cm-3. This density agrees well with the density of positive carriers (assuming one hole per Sr atom) of 1.9x 1021cm-3. Similar conclusions for La1.825Sr0.175CuO4 were reached by Herr et al.3 based upon Kramers-Kronig (KK) analysis of their R data.