Browsing by Author "Klein, Olivier"

Now showing 1 - 5 of 5

Open Access
The electrodynamics of organic superconductors
(1993) Dressel, Martin; Degiorgi, Leonardo; Klein, Olivier; Grüner, George
The electrodynamics of two classes of organic superconductors, based on the molecule BEDT-TTF, and on C60, is discussed. For both groups of materials, in the normal state the frequency dependent conductivity is that of a weakly correlated metal (with an interband transition in the inared region). We find that for representative examples of both groups of organic materials the electrodynamics of the superconducting state is in full agreement with s-wave pairing.
Open Access
Electrodynamics of the organic superconductors κ-(BEDT-TTF)2Cu(NCS)2 and κ-(BEDT-TTF)2Cu[N(CN)2]Br
(1994) Dressel, Martin; Klein, Olivier; Grüner, George; Carlson, K. Douglas; Wang, H. Hau; Williams, Jack M.
We have performed measurements of the surface impedance in the normal and superconducting states of the title compounds in the millimeter wave-frequency range (1–3 cm-1), and have evaluated the complex conductivity for different crystallographic orientations. Above the transition temperature, the materials behave like metals with a scattering rate of approximately 20 cm-1. In the superconducting state the electrodynamics is in good agreement with calculations based on a BCS ground state: while the penetration depth and the coherence length are anisotropic, the superconducting energy gap shows no indications of line nodes.
Open Access
Microwave cavity perturbation technique. Part 1, Principles
(1993) Klein, Olivier; Donavan, Steve; Dressel, Martin; Grüner, George
This report reviews the analysis used to extract the complex conductivity of a compound from a microwave cavity perturbation measurement. We intend to present a generalized treatment valid for any spheroidally shaped sample of arbitrary conductivity which is placed at either the electric or magnetic field antinode of the cavity. To begin with, we establish the relationship between the measured parameters and the conductivity for a spherical sample. Next, we extend these results to the case of spheroids; and for the first time, we cover all different configurations that one can possibly use to study an arbitrary conducting sample inside a cavity: in particular, all possible orientations of the sample with respect to the applied field are solved.
Open Access
Microwave cavity perturbation technique. Part 2, Experimental scheme
(1993) Donavan, Steve; Klein, Olivier; Dressel, Martin; Holczer, Karoly; Grüner, George
In this paper, the second in a three part series, we describe an experimental scheme used to measure the electrodynamical response of a material in the millimeter wave range of frequency. In particular, with this technique we can directly evaluate the complex conductivity from a measurement ofboth the bandwidth and characteristic frequency of a resonator containing the specimen. We will describe in detail all the technical improvements achieved which provide the required accuracy.
Open Access
Microwave cavity perturbation technique. Part 3, Applications
(1993) Dressel, Martin; Klein, Olivier; Donavan, Steve; Grüner, George
The resonant cavity perturbation method as described in the preceding two parts of this series is applied to study the electrodynamical properties of different materials in the microwave and millimeter wave spectral range. We briefly discuss the relevant uncertainties which are asociated with the different measurement techniques and we find that employing the amplitude technique it is possible to measure both the width and frequency to nearly the same precision. We then demonstrate the broad range of applicability of this technique by showing results obtained on several different materials, ranging from an insulator to a superconductor. The performance limitations of this technique are discussed in detail.