Magnetic oscillations in a two-dimensional network of compensated electron and hole orbits

The FS of (ET)8Hg4Cl12(C6H5Br)2 can be regarded as a 2D network of compensated electron and hole orbits coupled by magnetic breakthrough. Simultaneous measurements of the interlayer magnetoresistance and magnetic torque have been performed up to 28 T. Magnetoresistance and de dHvA oscillations spectra exhibit frequency combinations typical of such a network. Even though some of the observed magnetoresistance oscillations cannot be interpreted on the basis of neither conventional SdH oscillations nor quantum interference, the temperature and magnetic field (both orientation and magnitude) dependence of all the Fourier components of the dHvA spectra can be consistently accounted for by the LK formula. This behaviour is at variance with that currently reported for compounds illustrating the linear chain of coupled orbits model.Comment: accepted for publication in europhysics Letter

Competing types of quantum oscillations in the 2D organic conductor (BEDT-TTF)8Hg4Cl12(C6H5Cl)2

Interlayer magnetoconductance of the quasi-two dimensional organic metal (BEDT-TTF)8Hg4Cl12(C6H5Cl)2 has been investigated in pulsed magnetic fields extending up to 36 T and in the temperature range from 1.6 to 15 K. A complex oscillatory spectrum, built on linear combinations of three basic frequencies only is observed. These basic frequencies arise from the compensated closed hole and electron orbits and from the two orbits located in between. The field and temperature dependencies of the amplitude of the various oscillation series are studied within the framework of the coupled orbits model of Falicov and Stachowiak. This analysis reveals that these series result from the contribution of either conventional Shubnikov-de Haas effect (SdH) or quantum interference (QI), both of them being induced by magnetic breakthrough. Nevertheless, discrepancies between experimental and calculated parameters indicate that these phenomena alone cannot account for all of the data. Due to its low effective mass, one of the QI oscillation series - which corresponds to the whole first Brillouin zone area - is clearly observed up to 13 K.Comment: 8 pages, 8 figures. To be published in Phys. Rev.

High frequency magnetic oscillations of the organic metal θ\theta-(ET)4_4ZnBr4_4(C6_6H4_4Cl2_2) in pulsed magnetic field of up to 81 T

De Haas-van Alphen oscillations of the organic metal $\theta$-(ET)$_4$ZnBr$_4$(C$_6$H$_4$Cl$_2$) are studied in pulsed magnetic fields up to 81 T. The long decay time of the pulse allows determining reliable field-dependent amplitudes of Fourier components with frequencies up to several kiloteslas. The Fourier spectrum is in agreement with the model of a linear chain of coupled orbits. In this model, all the observed frequencies are linear combinations of the frequency linked to the basic orbit $\alpha$ and to the magnetic-breakdown orbit $\beta$.Comment: 6 pages, 4 figure

Quantum oscillations in the linear chain of coupled orbits: the organic metal with two cation layers theta-(ET)(4)CoBr(4)(C(6)H(4)Cl(2))

Analytical formulae for de Haas-van Alphen (dHvA) oscillations in linear chain of coupled two-dimensional (2D) orbits (Pippard's model) are derived systematically taking into account the chemical potential oscillations in magnetic field. Although corrective terms are observed, basic (alpha) and magnetic breakdown-induced (beta and 2beta - alpha) orbits can be accounted for by the Lifshits-Kosevich (LK) and Falicov-Stachowiak semiclassical models in the explored field and temperature ranges. In contrast, the 'forbidden orbit' beta - alpha amplitude is described by a non-LK equation involving a product of two classical orbit amplitudes. Furthermore, strongly non-monotonic field and temperature dependence may be observed for the second harmonics of basic frequencies such as 2alpha and the magnetic breakdown orbit beta + alpha, depending on the value of the spin damping factors. These features are in agreement with the dHvA oscillation spectra of the strongly 2D organic metal theta- theta-(ET)(4)CoBr(4)(C(6)H(4)Cl(2)).Comment: to be published in Europhysics Letters (2012

Optical properties of organic conductor (ET)4_4Hg3_3I8_8 : alternative type of electron-vibrational interaction

The reflectivity spectra of single crystals of (ET)$_4$Hg$_3$I$_8$ and (d$_8$-ET)$_4$Hg$_3$I$_8$ were studied. In contrant with earlier studied clorine- and brominemercurate compounds of the series (ET)$_4$Hg$_{3 - \delta}$ - X$_8$ (X = Cl, Br, I), the spectra of iodinemercurate compounds exhibit low reflectivity without well-defined plasma edge and without electron-vibrational bands in the region 1 000 - 1 400 cm$^{-1}$. The latter fact may be due to electron-vibrational interaction with non-totally symmetric modes which may originate from peculiarities of crystal structure of iodinemercurate compounds. A phase transition of the first type is observed both for (ET)$_4$Hg$_3$I$_8$ and (d$_8$-ET)$_4$Hg$_3$I$_8$. At the transition temperature a jump in conductivity and reflectivity is observed

Anisotropy of Magnetoresistance and Shubnikov-de Haas Oscillations in Organic Metal (ET)3\text{}_{3}CuCl4\text{}_{4} • H2\text{}_{2}O

Behavior of the magnetoresistance has been studied in organic quasi two-dimensional metal (ET)$\text{}_{3}$CuCl$\text{}_{4}$•H$\text{}_{2}$O. Shubnikov-de Haas oscillations have been observed at the magnetic field directions near H ∥ c*. The oscillations frequency at H ∥ c* equals 45 T that corresponds approximately to 1% of the first Brillouin zone cross-section. The angle dependence of the oscillations frequency allows one to imagine at least the part of Fermi surface in the form of cylinder with an axis along c*

Crossover from the weak to strong-field behavior of the longitudinal interlayer magnetoresistance in quasi-two-dimensional conductors

We investigate the monotonic growth of longitudinal interlayer magnetoresistance $\bar{R}_{zz}(B_z)$, analytically and numerically in the self-consistent Born approximation. We show that in a weak magnetic field the monotonic part of $\bar{R}_{zz}(B_z)$ is almost constant and starts to grow only above the crossover field $B_{c}$, when the Landau levels (LL) become isolated, i.e. when the LL separation becomes greater than the LL broadening. In higher field $B_{z}>>B_{c}$, $\bar{R}_{zz}(B_{z}) \propto B_{z}^{1/2}$ in agreement with previous works.Comment: 5 pages, 3 figure