Cyclotron effective masses in layered metals

Many layered metals such as quasi-two-dimensional organic molecular crystals show properties consistent with a Fermi liquid description at low temperatures. The effective masses extracted from the temperature dependence of the magnetic oscillations observed in these materials are in the range, m^*_c/m_e \sim 1-7, suggesting that these systems are strongly correlated. However, the ratio m^*_c/m_e contains both the renormalization due to the electron-electron interaction and the periodic potential of the lattice. We show that for any quasi-two-dimensional band structure, the cyclotron mass is proportional to the density of states at the Fermi energy. Due to Luttinger's theorem, this result is also valid in the presence of interactions. We then evaluate m_c for several model band structures for the \beta, \kappa, and \theta families of (BEDT-TTF)_2X, where BEDT-TTF is bis-(ethylenedithia-tetrathiafulvalene) and X is an anion. We find that for \kappa-(BEDT-TTF)_2X, the cyclotron mass of the \beta-orbit, m^{*\beta}_c, is close to 2 m^{*\alpha}_c, where m^{*\alpha}_c is the effective mass of the \alpha- orbit. This result is fairly insensitive to the band structure details. For a wide range of materials we compare values of the cyclotron mass deduced from band structure calculations to values deduced from measurements of magnetic oscillations and the specific heat coefficient.Comment: 12 pages, 3 eps figure

Shubnikov-de Haas Oscillations in New Organic Conductors (ET)8\mathsf{_8}[ Hg4\mathsf{_4}Cl12\mathsf{_{12}}(C6\mathsf{_6}H5\mathsf{_5}Cl)2\mathsf{_2}] and (ET)8\mathsf{_8}[ Hg4\mathsf{_4}Cl12\mathsf{_{12}}(C6\mathsf{_6}H5\mathsf{_5}Br)2\mathsf{_2}]

The results of the investigations of Shubnikov-de Haas oscillations in the quasi-two-dimensional organic complexes (ET)${_8}$[ Hg$_4$Cl$_{12}$(C$_6$H$_5$Cl)$_2$] , where X = CI, Br in the magnetic fields up to 40 T were reported. These results allow one to obtain some information about Fermi surface in the mentioned complexes. Shubnikov-de Haas oscillations in the compound with X = Cl correspond at least to two different cylindrical sheets of Fermi surface with the cross-section in (bc)-plane of 13% and 20% Brillouin zone cross-section. Shubnikov-de Haas oscillations in the complex with X = Br correspond to one cylindrical sheet with the cross-section in (bc)-plane of 13% of Brillouin zone cross-section. The experimental results for the complex with X = Br more agree with the theoretical calculations of Fermi surface than for the complex with X = Cl.

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

Quantum and semiclassical oscillations in the organic metal, (BEDO-TTF)(2)Cl-x(H2O)(y)

Contains fulltext : 112512.pdf (publisher's version ) (Open Access

New ambient pressure organic superconductor with T-c=8.1 K based on unsymmetrical donor molecule, ethylenedithiotetrathiafulvalene: (EDT-TTF)(4)Hg3-delta I8, delta similar to 0.1-0.2

Contains fulltext : 58779.pdf (publisher's version ) (Closed access)The new ambient pressure organic superconductor based on unsymmetrical donor, ethylenedithiotetrathiafulvalene, and the iodomercurate anion. (EDT-TTF)(4)Hg3-deltaI8, delta similar to 0.1-0.2, with T-c = 8.1 K has been synthesized. Transport and magnetic properties have been investigated. Upper critical fields have been studied under parallel and perpendicular magnetic fields up to 17 T in the temperature region down to 1.3 K. The data show that upper critical fields are within the paramagnetic limit in all directions. The coherence lengths indicate that (EDT-TTT)(4)Hg3-deltaI8, delta similar to 0.1-0.2, is a quasi-two-dimensional organic superconductor. (C) 2003 Elsevier B.V. All rights reserved

New ambient pressure organic superconductor with Tc = 8.1 K: (EDT-TTF)4Hg3-3II

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Characterization of the Fermi surface of (BEDO-TTF)(5)- CsHg(SCN)(4) (2) by magnetoresistance measurements and tight-binding band structure calculations

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BETS4\mathsf{_4}CU2\mathsf{_2}Cl6\mathsf{_6} and BETS2\mathsf{_2}Fe0.75\mathsf{_{0.75}}Ga0.25\mathsf{_{0.25}}Cl4\mathsf{_4}, New Organic Metals of the BETS Family: Synthesis, Structure, and Properties

BETS salts (where BETS is bis(ethylenedithio)tetraselenafulvalene) with the CuCl$_3$, Cu$_2$Cl$_6$, (CuCl$_4$)$_n$ and Fe$_{0.75}$Ga$_{0.25}$Cl$_4$ anions have been synthesized. The physical properties of $\theta$-BETS$_4$Cu$_2$Cl$_6$ and $\kappa$-BETS$_2$(Fe$_{0.75}$Ga$_{0.25}$Cl$_4$) salts and crystal structures of $\theta$-BETS$_4$Cu$_2$Cl$_6$ have been studied. Both compounds have been found to exhibit Shubnikov-de Haas and angle-dependent magnetoresistance oscillations.