15 research outputs found
Shubnikov-de Haas oscillations spectrum of the strongly correlated quasi-2D organic metal (ET)8[Hg4Cl12(C6H5Br)]2 under pressure
Pressure dependence of the Shubnikov-de Haas (SdH) oscillations spectra of
the quasi-two di- mensional 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 resistanceComment: Eur. Phys. J. B, in pres
Onsager phase factor of quantum oscillations in the organic metal theta-(BEDT-TTF)4CoBr4(C6H4Cl2)
De Haas-van Alphen oscillations are studied for Fermi surfaces illustrating
the Pippard's model, commonly observed in multiband organic metals. Field- and
temperature-dependent amplitude of the various Fourier components, linked to
frequency combinations arising from magnetic breakdown between different bands,
are considered. Emphasis is put on the Onsager phase factor of these
components. It is demonstrated that, in addition to the usual Maslov index,
field-dependent phase factors must be considered to precisely account for the
data at high magnetic field. We present compelling evidence of the existence of
such contributions for the organic metal theta-(BEDT-TTF)4CoBr4(C6H4Cl2)
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.
Temperature- and pressure-dependent metallic states in (BEDT-TTF)8[Hg4Br12(C6H5Br)2]
Temperature-driven metal-insulator and pressure-driven insulator-metal
transitions observed in(BEDT-TTF)8[Hg4X12(C6H5Y)2]] with X = Y = Br are studied
through band structure calculations based on X-ray crystal structure
determination and Shubnikov-de Haas (SdH) oscillations spectra, respectively.
In connection with chemical pressure effect, the transition, which is not
observed for X = Cl, is due to gap opening linked to structural changes as the
temperature decreases. Even though many body interactions can be inferred from
the pressure dependence of the SdH oscillations spectra, all the data can be
described within a Fermi liquid picture
Crystal structure, Fermi surface calculations and Shubnikov-de Haas oscillations spectrum of the organic metal -(BETS)HgBr(CHCl) at low temperature
The organic metal \theta_4_4_6_5$Cl) is known to
undergo a phase transition as the temperature is lowered down to about 240 K.
X-ray data obtained at 200 K indicate a corresponding modification of the
crystal structure, the symmetry of which is lowered from quadratic to
monoclinic. In addition, two different types of cation layers are observed in
the unit cell. The Fermi surface (FS), which can be regarded as a network of
compensated electron and hole orbits according to band structure calculations
at room temperature, turns to a set of two alternating linear chains of orbits
at low temperature. The field and temperature dependence of the Shubnikov-de
Haas oscillations spectrum have been studied up to 54 T. Eight frequencies are
observed which, in any case, points to a FS much more complex than predicted by
band structure calculations at room temperature, even though some of the
observed Fourier components might be ascribed to magnetic breakdown or
frequency mixing. The obtained spectrum could result from either an interaction
between the FS's linked to each of the two cation layers or to an eventual
additional phase transition in the temperature range below 200 K.Comment: accepted for publication in Solid State Science
Effect of External Pressure on the MetalâInsulator Transition of the Organic Quasi-Two-Dimensional Metal K-(BEDT-TTF)2Hg(SCN)2Br
The metalâinsulator transition in the organic quasi-two-dimensional metal Îș-(BEDT-TTF)2Hg(SCN)2Br at TMI â 90 K has been investigated. The crystal structure changes during this transition from monoclinic above TMI to triclinic below TMI. A theoretical study suggested that this phase transition should be of the metal-to-metal type and brings about a substantial change of the Fermi surface. Apparently, the electronic system in the triclinic phase is unstable toward a Mott insulating state, leading to the growth of the resistance when the temperature drops below TMI â 90 K. The application of external pressure suppresses the Mott transition and restores the metallic electronic structure of the triclinic phase. The observed quantum oscillations of the magnetoresistance are in good agreement with the calculated Fermi surface for the triclinic phase, providing a plausible explanation for the puzzling behavior of Îș-(BEDT-TTF)2Hg(SCN)2Br as a function of temperature and pressure around 100 K. The present study points out interesting differences in the structural and physical behaviors of the two room temperature isostructural salts of Îș-(BEDT-TTF)2Hg(SCN)2X with X = Br, Cl.The work at the Federal Research Center of Problems of Chemical Physics and Medicinal
Chemistry was carried out within the project of state assignment number AAAA-A19-119092390079-8.
V.N.Z. acknowledges the support of the Russian Foundation for Basic Research No. 21-52-12027.
The work in Spain was supported by the MICIU (Grant PGC2018-096955-B-C44) and Generalitat de
Catalunya (2017SGR1506). E.C. acknowledges the support of the Spanish MICIU through the Severo
Ochoa FUNFUTURE (CEX2019-000917-S) Excellence Center distinction.With funding from the Spanish government through the âSevero Ochoa Centre of Excellenceâ accreditation (CEX2019-000917-S).Peer reviewe