Matthew J. Holcomb

Raman spectra of YBa2Cu3Ox superconductors with different oxygen content

The Raman spectra of high-purity samples of YBa/sub 2/Cu/sub 3/O/sub x/ were studied as a function of oxygen content 6

Thermal difference spectroscopy

We have developed a simple method of collecting the thermal derivative spectra of solids. In this method, a sample’s reflectance is measured at two specific temperatures and the thermal difference of the material’s reflectance is calculated. By digitally averaging these differences, we obtain spectra equivalent to thermal modulation spectra. Since this is not a modulation technique we have named it thermal difference spectroscopy. Using the thermal difference spectrometer we have achieved a base line noise level in the normalized thermal difference reflectance spectrum (ΔR/R) of approximately 5×10−5. To demonstrate the technique’s utility as a truly noncontact derivative spectroscopy we have collected thermal difference spectra of both thin‐film and bulk samples.

New phenomena in proximity effect tunneling of high Tc superconducting cuprates

Abstract A new type of geometric oscillation in the differential resistance of proximity effect junctions has been observed. The oscillations have been seen in Ag-High-T c -Tl(2223) cuprate sandwiches using a new tunneling technique-distributed point contact tunneling. The oscillations are similar to Tomasch-Rowell oscillations but exhibit no thermal broadening. They arise from multiple-reflection interference of the center-of-mass pair wave function across the Ag-film. The sandwiches exhibit a proximity effect at 80K which extends over a distance more than fifty times the Pippard coherence length. We explain the phenomenon using a BCS-type pairing model.

Thermal difference reflectance spectroscopy of high-Tc superconductors

The temperature dependent thermal difference reflectance (TDR) spectra of thin film samples of Tl2Ba2Ca2Cu3O10, (BiPb)2Sr2Ca2Cu3O10, Tl2Ba2CaCu2O8 and YBa2Cu3O7 have been measured for photon energies between 0.3 and 4.5 eV at temperatures above and below each materials superconducting critical temperature. The amplitude of the characteristic optical structure near the screened plasma frequency of each sample in the normal state TDR spectrum varies approximately linearly with temperature, T, indicating that the temperature dependent optical scattering rate in these materials scales with temperature as T2. From the TDR spectra collected above and below the critical temperature of each sample, the superconducting to normal state reflectance ratio, Rs/RN, has been obtained. In these materials, a feature exists in the experimental Rs/RN spectrum at energies between 1.5 and 2.0 eV which can be accounted for by treating the superconductivity in an Eliashberg model with a coupling function that includes both an electron-phonon interaction and a high energy electron-boson interaction located between 1.6 and 2.1 eV. Good agreement is obtained between theory and experiment based upon this description of the superconducting state.

Uncovering the gap, Δ(ω): Measurement of the Re(σS/σN) in superconducting Tl2Ba2CaCu2O8

Abstract We report measurements of both the normal-state reflectance and the superconducting- to normal-state reflectance ratio of a thin film sample of Tl 2 Ba 2 CaCu 2 O 8 at near-normal incidence for photon energies between 0.09 and 4.5 eV. From these data we have obtained the real part of the superconducting- to normal-state optical conductivity ratio, Re(σ S /σ N ). This quantity can be related directly to structure in Δ(ω) without the need to invoke Eliashberg theory. We find structure in Δ(ω) for superconducting Tl 2 Ba 2 CaCu 2 O 8 at low-energy, presumably due to electron-phonon coupling, and additional structure at approximately 1.2 eV and 1.7eV which we attribute to an electronic component of the pairing interaction in this material.

Thermal modulation spectroscopy of the high transition temperature superconductors

Abstract Thermal modulation spectroscopy is a powerful technique for the determination of the properties of the normal state of metals and semiconductors, giving as it does, evidence of interband transitions, phonon singularities and plasma frequencies. We will report progress on experimental work using this technique to determine the plasma frequency of the high T c superconductor, Y 1 Ba 2 Cu 3 O 7−x .

Raman spectra of YBa/sub 2/Cu/sub 3/O/sub x/ superconductors with different oxygen content

The Raman spectra of high-purity samples of YBa/sub 2/Cu/sub 3/O/sub x/ were studied as a function of oxygen content 6

Raman spectra ofYBa2Cu3Oxsuperconductors with different oxygen content

The Raman spectra of high-purity samples of YBa/sub 2/Cu/sub 3/O/sub x/ were studied as a function of oxygen content 6