Magnetotransport in Quasi-Two-Dimensional Organic Conductors Based on BEDT-TTF and its Derivatives

In this short review we discuss the magnetotransport properties of the most popular series of quasi-two-dimensional organic metals and superconductors, namely $\beta$-, $k$- and $\alpha$-salts of BEDT-TTF (shortly, Et) and some compounds based on the ET derivatives, BEDO-TTF and BEDT-TSeF. We concentrate on the results of the Fermi surface studies obtained by means of Shubnikov-de Haas as well as a new very informative angle-dependent semi-classical magnetoresistance oscillations (AMRO) experiments. The results reported here were obtained mainly due to close collaboration of different physical and chemical groups in Chernogolovka (Russia), which have been organized and led by Prof. I.F. Schegolev

Pressure effect on M-I transition and phase diagram of an organic conductor (ET)2Br⋅C2H4(OH)2\mathsf{({\rm ET})_{2}{\rm Br}\cdot {\rm C}_{2}{\rm H}_{4}({\rm OH})_{2}}

The electrical resistance of an organic conductor (ET)$_{2}$Br$\cdot$ C$_{2}$H$_{4}$(OH)$_{2}$ has been measured under pressure. This compound exhibits a metal-insulator transition of the first order. The transition temperature was found to increase with increasing the pressure, with the resistance decrease when passing into the insulator state at pressures higher than 1.8 kbar. The phase diagram is presented

Giant angular magnetoresistance oscillations in (BEDT-TTF)2_{\bf 2} TlHg(SCN)4_{\bf 4} : the warped plane Fermi surface effect

Measurements of magnetoresistance anisotropy in a quasi-two-dimensional conductor (BEDT-TTF)$_2$TlHg(SCN)$_4$ have been performed. Giant angular magnetoresistance oscillations have been found upon rotating the magnetic field in different planes perpendicular to the highly conducting ac-plane. The phenomenon is proposed to be associated with specifics of th electron motion along the open FS sheets under the magnetic field. The analysis of the oscillations reveals some qualitative differences between a calculated high temperature position of the open Fermi surface sheets and that found at low temperatures

Angular magnetoresistance oscillations and the shape of the Fermi surface in β\mathsf{\beta}(ET)2_2IBr2_2

Angular magnetoresistance oscillations have been studied systematically for $\beta$-(ET)$_2$ IBr$_2$ in the magnetic field rotating in a series of planes perpendicular to the conducting (a, b)-plane. The oscillations have been found in all studied planes. The shape of the Fermi surface transverse cross-section has been reconstructed using the obtained data. Angular dependence of the slow Shubnikov-de Haas oscillations frequency and some fine features of angular magnetoresistance oscillations permit to discuss also the structure of the Fermi surface longitudinal cross-section. The Fermi surface consists most likely of main cylinders with inclined warping planes and small pockets or necks between them

Magnetic Field-Induced Phase Transition in the Quasi Two-Dimensional Organic Superconductor (BEDO-TTF)2\mathsf{_2}ReO4\mathsf{_4} ⋅\cdotH2\mathsf{_2}O

Transverse magnetoresistance of the two-dimensional (2D) organic superconductor (BEDO-TTF)$_2$ReO$_4$ $\cdot$H$_2$O has been measured in pulsed magnetic fields up to 52 T and in the temperature range from 1.7 K to 4.2 K. For magnetic field lower than ~15 T, applied perpendicularly to the conducting planes, the data are in good agreement with previous studies, namely, the two Shubnikov-de Haas oscillation series with frequency $F_1 =(38\pm 2)$ T and $F_2=(74\pm 2)$ T attributed to electron and hole orbits, respectively, are observed. However, as the magnetic field is rotated in the plane perpendicular to the best conductivity direction, the behaviour of the oscillations is not consistent with a perfect 2D picture. In addition, a new oscillation series with frequency about twice $F_2(F_4=(150\pm 10)$ T) rises up at high magnetic field while the amplitude of the oscillations with the $F_2$ frequency decreases. Furthermore, magnetic fields higher than 10 T, applied parallel to the conducting planes, yield negative magnetoresistance. These features are discussed on the basis of the available Fermi surface calculations

Magnetoresistance oscillations up to 32 K in the organic metal β″-(ET)₄(H₃O)[Fe(C₂O₄)₃]⋅C₆H₄Cl₂

Magnetic torque and magnetoresistance of the quasi-two-dimensional charge transfer salt β″-(ET)₄(H₃O)[Fe(C₂O₄)₃]⋅C₆H₄Cl₂ have been investigated in pulsed magnetic fields of up to 55 T. At variance with de Haas–van Alphen oscillations, Shubnikov–de Haas oscillations are observed up to temperatures as high as 32 K at ambient pressure despite a significant thermal damping in the low-temperature range. This feature, observed under applied pressure as well, is interpreted on the basis of the coexistence of a closed orbit and a quantum interference path with the same cross section

Metallic phase stabilization and phase diagram of (ET)3(HSO4)2\mathsf{(ET)_{3}(HSO_{4})_{2}}

A novel way for obtaining (ET)$_{3}$(HSO$_{4}$)$_{2}$ single crystals is reported. The metallic state of (ET)$_{3}$(HSO$_{4}$)$_{2}$ is stabilized at the pressure of 7.5 kbar. The metal-insulator phase transition is found to be of the second order. The phase diagram of (ET)$_{3}$(HSO$_{4}$)$_{2}$ is presented

Magnetoresistance oscillations up to 32 K in the organic metal "-(ET)4(H3O)[Fe(C2O4)3]C6H4Cl2

International audienc

Magnetoresistance oscillations up to 32 K in the organic metal "-(ET)4(H3O)[Fe(C2O4)3]C6H4Cl2

International audienc