Prof Arzhang Ardavan

Abstract:

We report high-field magnetotransport measurements oil beta"-(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 m(eff) approximate to 0.5 - 1.1 m(e) whereas the Dingle temperatures varies between T-D approximate to 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.

Abstract:

We present the results of numerical calculations of the energy levels and eigenfunctions of finite sections of a tight-binding square lattice in the presence of a perpendicular magnetic field. The energy spectrum of such a system, plotted as a function of magnetic field, resembles the Hofstadter butterfly found for the infinite system. In high magnetic fields, each eigenstate carries a persistent current which has a chirality associated with whether the eigenstate exists in the bulk or the edge of the system. We present simulations of electric dipole transitions between the chirally distinguished states for an isotropic lattice. These transitions correspond to harmonics in the cyclotron resonance.

Abstract:

We report millimetre-wave and magnetic measurements on single crystals of the high-spin molecular magnet, Cr-10(OMe)(20)(O2CCMe3)(10). The susceptibility data obtained using a SQUID magnetometer indicate that this molecule has a total spin of S = 15. The temperature dependence of the magnetisation allows us to estimate the intermolecular exchange constant. The EPR spectra were obtained at different frequencies, angles and temperatures. The results are compared with numerical simulations allowing determination of the Hamiltonian parameters.

Abstract:

We report in magnetotransport measurements performed in magnetic fields of up to 33 T and at low temperatures (0.45 K

More details from the publisher