127 research outputs found
Effect of electronic band dispersion curvature on de Haas-van Alphen oscillations
The effect of electronic band curvature, i.e. the deviation from parabolicity
of electronic dispersion, on de Haas-van Alphen oscillations spectra is
studied. Although the oscillations amplitude remain unaffected, it is
demonstrated that non-quadratic terms of the Landau bands dispersion, which is
particularly relevant in the case of Dirac fermions, induces a field- and
temperature-dependent Onsager phase. As a result, a temperature-dependent shift
of the de Haas-van Alphen oscillations frequency is predicted.Comment: 16 pages, 2 figure
de Haas-van Alphen oscillations with non-parabolic dispersions
de Haas-van Alphen oscillation spectrum of two-dimensional systems is studied
for general power law energy dispersion, yielding a Fermi surface area of the
form for a given energy . The case stands
for the parabolic energy dispersion. It is demonstrated that the periodicity of
the magnetic oscillations in inverse field can depend notably on the
temperature. We evaluated analytically the Fourier spectrum of these
oscillations to evidence the frequency shift and smearing of the main peak
structure as the temperature increases.Comment: 14 pages, 2 figures, to appear in Eur. Phys. J.
Random walks and magnetic oscillations in compensated metals
The field- and temperature-dependent de Haas-van Alphen oscillations spectrum
is studied for an ideal two-dimensional compensated metal whose Fermi surface
is made of a linear chain of successive orbits with electron and hole
character, coupled by magnetic breakdown. We show that the first harmonics
amplitude can be accurately evaluated on the basis of the Lifshits-Kosevich
(LK) formula by considering a set of random walks on the orbit network, in
agreement with the numerical resolution of semi-classical equations.
Oppositely, the second harmonics amplitude does not follow the LK behavior and
vanishes at a critical value of the field-to-temperature ratio which depends
explicitly on the relative value between the hole and electron effective
masses.Comment: 9 pages, 10 figures. Submitted to Physical Review
Quantum oscillations and upper critical magnetic field of the iron-based superconductor FeSe
Shubnikov-de Haas (SdH) oscillations and upper critical magnetic field
() of the iron-based superconductor FeSe ( = 8.6 K) have been
studied by tunnel diode oscillator-based measurements in magnetic fields of up
to 55 T and temperatures down to 1.6 K. Several Fourier components enter the
SdH oscillations spectrum with frequencies definitely smaller than predicted by
band structure calculations indicating band renormalization and reconstruction
of the Fermi surface at low temperature, in line with previous ARPES data. The
Werthamer-Helfand-Hohenberg model accounts for the temperature dependence of
for magnetic field applied both parallel (\textbf{H} ) and
perpendicular (\textbf{H} ) to the iron conducting plane, suggesting
that one band mainly controls the superconducting properties in magnetic fields
despite the multiband nature of the Fermi surface. Whereas Pauli pair breaking
is negligible for \textbf{H} , a Pauli paramagnetic contribution is
evidenced for \textbf{H} with Maki parameter = 2.1,
corresponding to Pauli field = 36.5
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
De Haas-van Alphen oscillations in the compensated organic metal alpha-'pseudo-kappa'-(ET)4H3O[Fe(C2O4)3].(C6H4Br2)
Field-, temperature- and angle-dependent Fourier amplitude of de Haas-van
Alphen (dHvA) oscillations are calculated for compensated two-dimensional (2D)
metals with textbook Fermi surface (FS) composed of one hole and two electron
orbits connected by magnetic breakdown. It is demonstrated that, taking into
account the opposite sign of electron and hole orbits, a given Fourier
component involves combination of several orbits, the contribution of which
must be included in the calculations. Such FS is observed in the strongly 2D
organic metal alpha-'pseudo-kappa'-(ET)4H3O[Fe(C2O4)3].(C6H4Br2), dHvA
oscillations of which have been studied up to 55 T for various directions of
the magnetic field with respect to the conducting plane. Calculations are in
good quantitative agreement with the data.Comment: European Physical Journal B (2014
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)
Pressure dependence of the magnetoresistance oscillations spectrum of beta''-(BEDT-TTF)4(NH4)[Fe(C2O4)3].DMF
The pressure dependence of the interlayer magnetoresistance of the quasi-two
dimensional organic metal beta''-(BEDT-TTF)4(NH4)[Fe(C2O4)3].DMF has been
investigated up to 1 GPa in pulsed magnetic fields up to 55 T. The Shubnikov-de
Haas oscillations spectra can be interpreted on the basis of three compensated
orbits in all the pressure range studied, suggesting that the Fermi surface
topology remains qualitatively the same as the applied pressure varies. In
addition, all the observed frequencies, normalized to their value at ambient
pressure, exhibit the same sizeable pressure dependence. Despite this behavior,
which is at variance with that of numerous charge transfer salts based on the
BEDT-TTF molecule, non-monotonous pressure-induced variations of parameters
such as the scattering rate linked to the various detected orbits are observed.Comment: accepted for publication in Phys. Rev.
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
Analytical treatment of the dHvA frequency combinations due to chemical potential oscillations in an idealized two-band Fermi liquid
de Haas-van Alphen oscillation spectrum is studied for an idealized
two-dimensional Fermi liquid with two parabolic bands in the case of canonical
(fixed number of quasiparticles) and grand canonical (fixed chemical potential)
ensembles. As already reported in the literature, oscillations of the chemical
potential in magnetic field yield frequency combinations that are forbidden in
the framework of the semiclassical theory. Exact analytical calculation of the
Fourier components is derived at zero temperature and an asymptotic expansion
is given for the high temperature and low magnetic field range. A good
agreement is obtained between analytical formulae and numerical computations.Comment: 10 pages, 4 figure
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