38 research outputs found
Comment on "Magnetic quantum oscillations of the conductivity in layered conductors"
We discuss the recent theory of Gvozdikov [Phys. Rev. B 70, 085113 (2004)]
which aims at explaining the Shubnikov-de Haas oscillations of the longitudinal
resistivity \rho_zz observed in the quasi-two-dimensional organic compound
\beta''-(BEDT-TTF)_2SF_5CH_2CF_2SO_3.
We point out that the self-consistent equations of the theory yielding the
longitudinal resistivity and the magnetic field dependence of the chemical
potential have been incorrectly solved. We show that the consideration of the
self-consistent Born approximation (which determines the relaxation rate in
Gvozdikov's paper) leads in fact to the complete absence of the longitudinal
conductivity \sigma_{zz} at leading order in high magnetic fields.Comment: 4 pages, no figur
Comment on ``London Theory for Superconducting Phase Transitions in External Magnetic Fields: Application to ''
The authors of the Letter PRL 89, 017004 (2002) predict nontrivial flux
lattice structures in UPt3 in vicinity of the superconducting transition
between the A and B phases for low magnetic fields, an important conclusion for
motivating future experiments. We show that the approach and the conclusions of
this Letter are wrong. The transitions between the different superconducting
phases in the mixed state are pointed out to be rather crossovers than real
second-order phase transitions within the most popular theoretical models of a
two-component superconducting order parameter for UPt3.Comment: 2 pages, submitted to Phys. Rev. Lett. (December 2002
De Haas-van Alphen effect in two- and quasi two-dimensional metals and superconductors
An analytical form of the quantum magnetization oscillations (de Haas-van
Alphen effect) is derived for two- and quasi two-dimensional metals in normal
and superconducting mixed states. The theory is developed under condition that
the chemical potential is much greater than the cyclotron frequency, which is
proved to be valid for using grand canonical ensemble in the systems of low
dimensionality. Effects of impurity, temperature, spin-splitting and vortex
lattice - in the case of superconductors of type II -, are taken into account.
Contrary to the three dimensional case, the oscillations in sufficiently pure
systems of low dimensionality and at sufficiently low temperatures are
characterized by a saw-tooth wave form, which smoothened with temperature and
concentration of impurities growth. In the normal quasi two-dimensional
systems, the expression for the magnetization oscillations includes an extra
factor expressed through the transfer integral between the layers. The
additional damping effect due to the vortex lattice is found. The criterion of
proximity to the upper critical field for the observation of de Haas-van Alphen
effect in the superconducting mixed state is established.Comment: 18 pages, Latex, revised versio
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.
Transport of Dirac quasiparticles in graphene: Hall and optical conductivities
The analytical expressions for both diagonal and off-diagonal ac and dc
conductivities of graphene placed in an external magnetic field are derived.
These conductivities exhibit rather unusual behavior as functions of frequency,
chemical potential and applied field which is caused by the fact that the
quasiparticle excitations in graphene are Dirac-like. One of the most striking
effects observed in graphene is the odd integer quantum Hall effect. We argue
that it is caused by the anomalous properties of the Dirac quasiparticles from
the lowest Landau level. Other quantities such as Hall angle and Nernst signal
also exhibit rather unusual behavior, in particular when there is an excitonic
gap in the spectrum of the Dirac quasiparticle excitations.Comment: 25 pages, RevTeX4, 8 EPS figures; final version published in PR
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
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
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
On the theory of superconductivity in ferromagnetic superconductors with triplet pairing
We point out that ferromagnetic superconductors with triplet pairing and
strong spin-orbit coupling are even in the simplest case at least two-band
superconductors. The Gor'kov type formalism for such superconductors is
developed and the Ginzburg-Landau equations are derived. The dependence of the
critical temperature on the concentration of ordinary point-like impurities is
found. Its nonuniversality could serve as a qualitative measure of the two-band
character of ferromagnetic superconductors. The problem of the upper critical
field determination is also discussed.Comment: 8 pages, no figure; important changes with respect to the previous
versions due to the correction of a mistake: in this new version, a more
general form is considered for the order parameter (the two-components of the
order parameter were considered before as equal, which is in general not
true) ; submitted to Physical Review