Far-IR excitations in Cd2Re2O7 in the normal and superconducting states

Cd(2)Re(2)O(7) is a pyrochlore superconductor with a transition temperature T(c) near 1 K. We report on the far-infrared optical properties of Cd(2)Re(2)O(7) at temperatures above and below T(c) with a particular emphasis on changes in the spectrum below T(c). Seventeen phonon modes are observed in the normal state optical conductivity spectrum of Cd(2)Re(2)O(7) at low temperatures in good agreement with a factor group analysis. In the superconducting state, a softening (~1 cm(-1)) of the phonon modes at 35 and 61 cm(-1) occurs and thermal reflectance spectra show the development of two additional strong absorption features, near 9.6 and 19.3 cm(-1). The dominant presence of lattice vibrational modes in the optical spectrum suggests that electron-phonon interaction plays an important role in the normal and superconducting state properties of Cd(2)Re(2)O(7).

Kramers-Kronig-constrained variational dielectric fitting and the reflectance of a thin film on a substrate

A test was made of the ability of Kramers-Kronig-constrained variational dielectric fitting to extract the optical conductivity of a thin film from reflectance data containing structure due to both thin film and substrate. The reflectance of a series of well-characterized thin films of SrRu(x)Mg(1-x)O(3) and SrRu(x)O(3) with a variety of thicknesses (approximately 56-300 nm) and dc resistivities (approximately 250-2200 micro Omega cm) was measured. The low frequency values of the extracted optical conductivities agree with the dc measurements, however, removal of features due to the substrate improves with increasing film thickness.

Emergence of coherent transport in UBe13: an optical investigation in both the normal and superconducting states

The far-infrared reflectance of heavy-fermion superconductor UBe13 has been measured from 0.5 K in the superconducting state, to 300 K. Coherent transport, characterized by an optical conductivity that exhibits a renormalized Drude peak at low frequencies, emerges between 45 and 85 K although the dc resistivity of UBe13 continues to increase with decreasing temperature down to approximately 2.5 K. In the superconducting state, the low frequency scattering rate falls abruptly, implying that the formation of the condensate alters dramatically the interaction between the heavy electrons.

Far-infrared resonance in Sr(2)RuO(4)

The far-infrared c-axis reflectance of Sr(2)RuO(4) has been measured above and below the 2.5 K superconducting transition temperature of the sample. A plasma edge develops near 70 cm(-1) as the temperature is lowered, which corresponds to a Drude peak in the real optical conductivity associated with the onset of the coherent motion of the carriers. A gaplike suppression of the frequency-dependent scattering rate at low temperatures indicates that the coherent transport is related to a loss of scattering below 60 cm(-1). A strong resonance near 9 meV is responsible for the scattering that destroys coherence.

Technique for measuring the reflectance of irregular, submillimeter-sized samples

Details are given of a technique for measuring the reflectance at near-normal incidence of small, irregular, submillimeter-sized samples from the far IR (40 cm(-1)) to the visible (40000 cm(-1)) between 10 and 300 K by using a modified Michelson interferometer or grating spectrometer. The sample and a reference mirror are mounted on nonreflecting cones. At the focus the size of the beam is larger than either the sample or the reference, so that the entire area of the sample is utilized. The positions are interchanged by a 90° rotation by using preset mechanical stops. The scattering caused by geometrical effects is corrected for by the in situ evaporation of gold or aluminum onto the sample. The effect of diffraction is estimated from Mie theory by assuming the sample and reference to be spheres. For frequencies above ≈ 40 cm(-1) and sample diameters of ≈ 1 mm with a detector field of view of 30°, the calculations show that the ratio of the backscattered intensities gives a good approximation of the specular reflectance.

A locus for X-linked congenital stationary night blindness is located on the proximal portion of the short arm of the X chromosome

Linkage between X-linked congenital stationary night blindness (CSNB1) and seven markers on the X chromosome was investigated in a large four-generation Albertan kindred. We detected significant linkage between the CSNB1 locus and the locus DXS255 (maximum lod score = 6.73 at a recombination fraction of 6%; confidence interval of 1% to 18%), which anchors the CSNB1 locus to the proximal region near p11.22 on the short arm of the X chromosome.

Variable expressivity in X-linked congenital stationary night blindness

X-linked congenital stationary night blindness (CSNB) is a well-documented disorder in which the most striking clinical features are impaired night vision, nystagmus and myopia. Recent reports have highlighted differing features between families, and it has been suggested that these discrepancies may be the result of two loci on the X chromosome or of two mutant alleles. We outline the clinical and visual function findings in 42 affected members from 10 families and 1 adopted person. There was a relative unawareness of the disorder in clinical practice. At least one of the main features of CSNB was absent in 75% of the patients. The visual function values varied widely, both between and within families (visual acuity 20/30 to 20/400, refractive error +1.50 to -22.50 and rod segment elevation 1.5 to 3.0 log units). The findings are consistent with a single allele exhibiting a wide variation in clinical expression.