D.A. Bonn

Far-infrared properties of ab -plane oriented YBa 2 Cu 3 O 7 − δ

Polycrystalline samples of YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ with a variety of surface treatments show differences in absolute reflectance and width of phonon lines. Samples that are not polished and are measured immediately after annealing have largely grains with the c axis normal to the surface. Such oriented samples show a gaplike depression of conductivity in the far infrared that sets in below the superconducting transition temperature but no true gap. Phonon lines at 195 cm/sup -1/ and at 155 cm/sup -1/ narrow in the superconducting state, in analogy with the effect of the electron-phonon interaction in Bardeen-Cooper-Schrieffer superconductors. In the normal state the background conductivity is Drudelike with a plasma frequency of 0.75 eV and a relaxation rate of 200 cm/sup -1/. The extrapolated far-infrared conductivity agrees with the measured dc conductivity.

Infrared properties of YBa2Cu3O7-δ

Abstract We review recent experimental data on the infrared properties of YBa 2 Cu 3 O 7-δ ceramics and single crystals. Kramers-Kronig analysis shows that the normal state far-infrared optical conductivity is dominated by a Drude response from free carriers with a plasma frequency of the order of 1.0 eV and a relaxation rate of 0.37 eV (300 cm -1 at 100 K. A strong mid-infrared band centered between 0.2 and 0.5 eV is seen in all the samples. Below the superconducting transition temperatures the far-infrared conductivity is depressed below 400 cm -1 but this is not a true energy gap since there remains, even in the best oriented crystal samples, a residual absorption.

FAR INFRARED OPTICAL-PROPERTIES OF HEAVY FERMION SUPERCONDUCTORS - UBE13 AND URU2SI2

Abstract We present far infrared reflectance measurements of UBe 13 and URu 2 Si 2 down to a temperature of 2 K. At low temperatures the optical conductivity of both materials may be described in terms of free charge carriers with frequency and temperature dependent scattering rates and mass enhancements. The ‘coherent regime’ occurs at too low a temperature in UBe 13 to be observed in our measurements, but it can be observed in URu 2 Si 2 . In addition to the behaviour of the charge carriers URu 2 Si 2 exhibits two strong phonon lines at 109 cm −1 and 378 cm −1 and below the magnetic transition temperature there is an additional absorbtion feature near 50 cm −1 .

Far-infrared ab plane reflectance and transmission of Bi2Sr2CaCu2O8

Abstract We review recent experimental data on the infrared thin film transmission and single crystal reflection spectra of Bi 2 Sr 2 CaCu 2 O 8 (T c ∼ 85 K). Both show that the low frequency response can be described by a Drude absorption with a relaxation rate for the carriers of the order of 100 cm −1 . This places the materials in the clean limit and no superconducting gap structure is evident. A temperature independent midinfrared absorption is present with a sharp onset at 300 cm −1 .

Infrared studies of textured ceramic high-Tc superconductors

The surfaces of ceramic samples of high-temperature superconductors can have a high degree of crystalline orientation, depending of the way in which they are prepared. (In particular it is essential that the sample not be polished in an attempt to “improve” the optical quality.) The surfaces of these textured ceramic samples consist of small crystallites, with about 80% orientation of the crystallographic c axis normal to the surface. The infrared and optical properties of these samples have been measured. We observe that the frequency-dependent conductivity can be decomposed into the sum of a far-infrared Drude part (which at zero frequency equals the ordinary dc conductivity) and a broad, temperature-independent mid-infrared band. The mid-infrared band has about four times the oscillator strength of the low-frequency Drude part.

Far-infrared properties ofab-plane orientedYBa2Cu3O7−δ

Polycrystalline samples of YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ with a variety of surface treatments show differences in absolute reflectance and width of phonon lines. Samples that are not polished and are measured immediately after annealing have largely grains with the c axis normal to the surface. Such oriented samples show a gaplike depression of conductivity in the far infrared that sets in below the superconducting transition temperature but no true gap. Phonon lines at 195 cm/sup -1/ and at 155 cm/sup -1/ narrow in the superconducting state, in analogy with the effect of the electron-phonon interaction in Bardeen-Cooper-Schrieffer superconductors. In the normal state the background conductivity is Drudelike with a plasma frequency of 0.75 eV and a relaxation rate of 200 cm/sup -1/. The extrapolated far-infrared conductivity agrees with the measured dc conductivity.

Far-infrared properties of ab-plane oriented YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/

Polycrystalline samples of YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ with a variety of surface treatments show differences in absolute reflectance and width of phonon lines. Samples that are not polished and are measured immediately after annealing have largely grains with the c axis normal to the surface. Such oriented samples show a gaplike depression of conductivity in the far infrared that sets in below the superconducting transition temperature but no true gap. Phonon lines at 195 cm/sup -1/ and at 155 cm/sup -1/ narrow in the superconducting state, in analogy with the effect of the electron-phonon interaction in Bardeen-Cooper-Schrieffer superconductors. In the normal state the background conductivity is Drudelike with a plasma frequency of 0.75 eV and a relaxation rate of 200 cm/sup -1/. The extrapolated far-infrared conductivity agrees with the measured dc conductivity.