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Shubnikov-de Haas (SdH) and de Haas-van Alphen (dHvA) oscillations spectra of the quasi-two dimensional charge transfer salt β′′-(ET)4(H3O)[ Fe(C2O4)3] .C6H4Cl2 have been investigated in pulsed magnetic fields up to 54 T. The data reveal three basic frequencies Fa, Fb and Fb - a, which can be interpreted on the basis of three compensated closed orbits at low temperature. However a very weak thermal damping of the Fourier component Fb, with the highest amplitude, is evidenced for SdH spectra above about 6 K. As a result, magnetoresistance oscillations are observed at temperatures higher than 30 K. This feature, which is not observed for dHvA oscillations, is in line with quantum interference, pointing to a Fermi surface reconstruction in this compound. [ABSTRACT FROM AUTHOR]

Pressure dependence of the Shubnikov-de Haas (SdH) oscillations spectra of the quasi-two dimensional organic metal (ET)8[ Hg4Cl12(C6H5Br)2] have been studied up to 1.1 GPa in pulsed magnetic fields of up to 54 T. According to band structure calculations, its Fermi surface can be regarded as a network of compensated orbits. The SdH spectra exhibit many Fourier components typical of such a network, most of them being forbidden in the framework of the semiclassical model. Their amplitude remains large in all the pressure range studied which likely rules out chemical potential oscillation as a dominant contribution to their origin, in agreement with recent calculations relevant to compensated Fermi liquids. In addition to a strong decrease of the magnetic breakdown field and effective masses, the latter being likely due to a reduction of the strength of electron correlations, a sizeable increase of the scattering rate is observed as the applied pressure increases. This latter point, which is at variance with data of most charge transfer salts is discussed in connection with pressure-induced features of the temperature dependence of the zero-field interlayer resistance. [ABSTRACT FROM AUTHOR]

The Shubnikov-de Haas (SdH) oscillation spectra of the $\beta''$ -(BEDT-TTF)4(NH4)[ Cr(C2O4)3] .DMF organic metal have been studied in pulsed magnetic fields of up to either 36 T at ambient pressure or 50 T under hydrostatic pressures of up to 1 GPa. The ambient pressure SdH oscillation spectra can be accounted for by up to six fundamental frequencies which points to a rather complex Fermi surface (FS). A noticeable pressure-induced modification of the FS topology is evidenced since the number of frequencies observed in the spectra progressively decreases as the pressure increases. Above 0.8 GPa, only three compensated orbits are observed, as it is the case for several other isostructural salts of the same family at ambient pressure. Contrary to other organic metals, of which the FS can be regarded as a network of orbits, no frequency combinations are observed for the studied salt, likely due to high magnetic breakdown gap values or (and) high disorder level evidenced by Dingle temperatures as large as ≃7 K. [ABSTRACT FROM AUTHOR]

The band structure of a-(Per)2M(mnt)2, leads to a description of these materials as nearly perfectly one dimensional conductors. The conduction is mainly along the stacking direction of the partially oxidized perylene molecules, (Per)1/2+, with virtually no interchain bandwidth. However, recent high magnetic field experiments suggest orbital coupling of the magnetic field to the electronic structure, indicating a finite interchain bandwidth. The details of the band structure and the possible variances, at low energies, from a perfect one dimensional system are examined. In particular, multiple quasi-one dimensional Fermi surface sheets, which would become important at low temperatures, may lead to an explanation for the experimental finding of a magnetic field induced high field charge density wave ground state. Experimental tests to observe the effects of the finite interchain bandwidth are proposed. [ABSTRACT FROM AUTHOR]

The interlayer magnetoresistance of the quasi-2D organic superconductor β″-(ET)4(NH4)[Fe(C2O4)3]·DMF has been investigated in pulsed magnetic fields of up to 55 T. According to band structure calculations, the Fermi surface results from the hybridisation of elliptical tubes yielding two compensated electron and hole orbits. Actually, the Fourier spectrum of the oscillatory magnetoresistance exhibits various frequencies which can be regarded as linear combinations of the two frequencies with the highest amplitude (Fa=(48±2) T and Fb=(241±5) T) corresponding to 1.2% and 6.0% of the first Brillouin zone area, respectively. The oscillatory spectrum can be accounted for by three compensated electron and hole orbits and combination frequencies typical of coupled orbits networks. [Copyright &y& Elsevier]