40 research outputs found
Incoherent interlayer electron hopping as a possible reason for enhanced magnetic quantum oscillations in the mixed state of a layered organic superconductor
We present a theory which is able to explain enhanced magnetic quantum-oscillation
amplitudes in the superconducting state of a layered organic metal with incoherent electronic
transport across the layers. The incoherence acts through the deformation of the layer-stacking
factor which becomes complex and decreases the total scattering rate in the mixed state. This novel
mechanism restores the coherence by establishing a long-range order across the layers and can
compensate the usual decrease of the Dingle factor below the upper critical magnetic field caused
by the intralayer scattering
Slow oscillations of magnetoresistance in quasi-two-dimensional metals
Slow oscillations of the interlayer magnetoresistance observed in the layered
organic metal -(BEDT-TTF)IBr are shown to originate from the
slight warping of its Fermi surface rather than from independent small
cyclotron orbits. Unlike the usual Shubnikov-de Haas effect, these oscillations
are not affected by the temperature smearing of the Fermi distribution and can
therefore become dominant at high enough temperatures. We suggest that the slow
oscillations are a general feature of clean quasi-two-dimensional metals and
discuss possible applications of the phenomenon.Comment: 11 pages, 3 figure
Spin-zero anomaly in the magnetic quantum oscillations of a two-dimensional metal
We report on an anomalous behavior of the spin-splitting zeros in the de
Haas-van Alphen (dHvA) signal of a quasi-two-dimensional organic
superconductor. The zeros as well as the angular dependence of the amplitude of
the second harmonic deviate remarkably from the standard Lifshitz-Kosevich (LK)
prediction. In contrast, the angular dependence of the fundamental dHvA
amplitude as well as the spin-splitting zeros of the Shubnikov-de Haas signal
follow the LK theory. We can explain this behavior by small chemical-potential
oscillations and find a very good agreement between theory and experiment. A
detailed wave-shape analysis of the dHvA signal corroborates the existence of
an oscillating chemical potential
De Haas-van Alphen Oscillations in the Quasi-Two-Dimensional Organic Conductor κ-(ET)2Cu(NCS)2: The Magnetic Breakdown Approach
We present both experimental data and an analytic theory for the de Haas–van Alphen ~dHvA! effect in the two-dimensional organic single-crystal conductor k -(ET)2Cu(NCS)2. We show that the magnetization oscillation pattern and the fast Fourier transform (FFT) spectrum of our measurements are well described theoretically within the coherent magnetic breakdown (MB) model for a two-dimensional Fermi surface consisting of two open sheets and closed pockets connected by magnetic breakdown centers. The spectrum of Landau quantized energy levels changes substantially due to the MB. Landau bands develop whose bandwidth and relative distance between them oscillate in inverse magnetic field. These oscillations explain the observed fine structure of the magnetization pattern at fields above the MB field with the occurrence of ‘‘forbidden’’ frequencies in the FFT spectrum
On the de Haas - van Alphen oscillations in quasi-two-dimensional metals: effect of the Fermi surface curvature
Here, we present the results of theoretical analysis of the de Haas-van
Alphen oscillations in quasi-two-dimensional normal metals. We had been
studying effects of the Fermi surface (FS) shape on these oscillations. It was
shown that the effects could be revealed and well pronounced when the FS
curvature becomes zero at cross-sections with extremal cross-sectional areas.
In this case both shape and amplitude of the oscillations could be
significantly changed. Also, we analyze the effect of the FS local geometry on
the angular dependencies of the oscillation amplitudes when the magnetic field
is tilted away from the FS symmetry axis by the angle We show that a
peak appears at whose height could be of the same order as
the maximum at the Yamaji angle. This peak emerges when the FS includes zero
curvature cross-sections of extremal areas. Such maximum was observed in
experiments on the The obtained results could be
applied to organic metals and other quasi-two-dimensional compounds.Comment: 9 pages, 4 figures, text added, references adde
Theory of the Shubnikov-de Haas effect in quasi-two-dimensional metals
The Shubnikov - de Haas effect in quasi-two-dimensional normal metals is
studied. The interlayer conductivity is calculated using the Kubo formula. The
electron scattering on short-range is considered in the self-consistent Born
approximation. The result obtained differs from that derived from the Boltzmann
transport equation. This difference is shown to be a general feature of
conductivity in magnetic field. A detailed description of the two new
qualitative effects -- the field-dependent phase shift of beats and of the slow
oscillations of conductivity is provided. The results obtained are applicable
to strongly anisotropic organic metals and to other quasi-two-dimensional
compounds.Comment: 10 page
Monotonic growth of interlayer magnetoresistance in strong magnetic field in very anisotropic layered metals
It is shown, that the monotonic part of interlayer electronic conductivity
strongly decreases in high magnetic field perpendicular to the conducting
layers. We consider only the coherent interlayer tunnelling, and the obtained
result strongly contradicts the standard theory. This effect appears in very
anisotropic layered quasi-two-dimensional metals, when the interlayer transfer
integral is less than the Landau level separation.Comment: 4 pages, no figure
Theory of de Haas-van Alphen Effect in Type-II Superconductors
Theory of quasiparticle spectra and the de Haas-van Alphen (dHvA) oscillation
in type-II superconductors are developed based on the Bogoliubov-de Gennes
equations for vortex-lattice states. As the pair potential grows through the
superconducting transition, each degenerate Landau level in the normal state
splits into quasiparticle bands in the magnetic Brillouin zone. This brings
Landau-level broadening, which in turn leads to the extra dHvA oscillation
damping in the vortex state. We perform extensive numerical calculations for
three-dimensional systems with various gap structures. It is thereby shown that
(i) this Landau-level broadening is directly connected with the average gap at
H=0 along each Fermi-surface orbit perpendicular to the field H; (ii) the extra
dHvA oscillation attenuation is caused by the broadening around each extremal
orbit. These results imply that the dHvA experiment can be a unique probe to
detect band- and/or angle-dependent gap amplitudes. We derive an analytic
expression for the extra damping based on the second-order perturbation with
respect to the pair potential for the Luttinger-Ward thermodynamic potential.
This formula reproduces all our numerical results excellently, and is used to
estimate band-specific gap amplitudes from available data on NbSe_2, Nb_3Sn,
and YNi_2B_2C. The obtained value for YNi_2B_2C is fairly different from the
one through a specific-heat measurement, indicating presence of gap anisotropy
in this material. C programs to solve the two-dimensional Bogoliubov-de Gennes
equations are available at http://phys.sci.hokudai.ac.jp/~kita/index-e.html .Comment: 16 pages, 11 figure
Magnetic Quantum Oscillations of the Longitudinal Conductivity in Quasi two-dimensional Metals
We derive an analytical expression for the longitudinal magnetoconductivity
in layered conductors in presence of a quantizing magnetic field
perpendicular to the layers and for short-range in-plane impurity scattering in
frame of the quantum transport theory. Our derivation points out quite unusual
temperature and magnetic field dependences for Shubnikov-de Haas oscillations
in the two-dimensional limit, i.e. , where is
the interlayer hopping integral for electrons, and the cyclotron
frequency. In particular, when and (here is the value of the
imaginary part of the impurity self-energy at the chemical potential ), a
pseudo-gap centered on integer values of appears in the
zero-temperature magnetoconductivity function
. At low temperatures, this high-field regime
is characterized by a thermally activated behavior of the conductivity minima
(when chemical potential lies between Landau levels) in correspondence
with the recent observation in the organic conductor
.Comment: 16 pages, 4 figures, to be published in Phys. Rev.