Prof Arzhang Ardavan

Abstract:

We report high-field magnetotransport measurements on β″-(BEDT- TTF)4[(H3O)M(C2O4) 3]· solvent, where M=Ga³⁺, Cr³⁺ and Fe³⁺ and solvent=C5H5N. In spite of their differing transition metal-ions, M, the three compounds exhibit similar magnetic quantum oscillation spectra superimposed on a positive magnetoresistance. At least four independent quantum oscillation frequencies have been identified, corresponding to two different hole and electron pockets of the Fermi surface which follow the rules of a compensated metal. Observation of the small pockets could be the result of the Fermi surface reconstruction induced by a possible density wave. The effective masses are very similar for different samples and for different pockets range between meff ≈ 0.5-1.1 me whereas the Dingle temperatures varies between TD ≈ 1.4-4 K. At low temperature, the longitudinal magnetoresistance violates Kohler's rule, suggesting that the interlayer transport in these quasi-2D systems cannot be related to a single scattering time and that the disorder plays an important role. © EDP Sciences.

Abstract:

We report magnetotransport measurements performed in magnetic fields of up to 33 T and at low temperatures (0.45 K4[(H3O)M(C2O4)3]· C6H5NO2, where the 3d metal ion M is either non-magnetic Ga³⁺ or magnetic Cr³⁺, Quantum oscillations suggest that the salt with M = Ga has two two-dimensional Fermi surface pockets (45 T and 230 T) whereas when M = Cr only one pocket (230 T) is observed. Replacing Ga with Cr has the effect of enhancing the effective mass of the 230 T pocket from 1.2 ± 0.2 me to 2.2 ± 0,3 me and reducing the superconducting critical temperature from Tc ≈ 8 K to Tc ≈ 5 K. © EDP Sciences.

Abstract:

An experimental implementation of an oscillating, superluminal polarization current distribution that undergoes centripetal acceleration was constructed and tested. The emission from the experimental machine was found to be tightly beamed in both the azimuthal and polar directions. It was found that the beaming is frequency independent and has a sharply defined and unchanging geometry determined only by the speed and path of the moving distribution pattern. The intensity of the radiation at these angles was observed to decline more slowly with increasing distance from the source than would the emission from a conventional antenna.