60 research outputs found
Giant Quantum Oscillations of the Longitudinal Magnetoresistance in Quasi two-dimensional Metals
We have investigated in frame of the quantum transport theory the magnetic
quantum oscillations of the longitudinal magnetoresistance in quasi
two-dimensional metals for a magnetic field perpendicular to the layers.
Giant Shubnikov-de Haas oscillations are found when the cyclotron energy
is much larger than the interlayer transfer integral
(the two-dimensional limit). In large magnetic fields and at low temperatures,
the minima of the magnetoconductivity exhibit a
thermally activated behavior in presence of negligibly small chemical potential
oscillations, as observed in the organic layered conductor
\beta''\mathrm{-(BEDT-TTF)}_{2}\mathrm{SF}_{5}\mathrm{CH}_{2}\mathrm{CF}_{2}\m
athrm{SO}_{3}.
The questions concerning the absence of strong chemical potential
oscillations in such compound and the impurity self-energy are discussed.Comment: 4 pages, intended for publication in special issue of Physica B for
RHMF 2003 Conference, Toulous
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
Reply to "Comment on 'Origin of combination frequencies in quantum magnetic oscillations of two-dimensional multiband metals' " by A.S. Alexandrov and A.M. Bratkovsky [cond-mat/0207173]
In their comment on the paper (Phys. Rev. B 65, 153403 (2002);
cond-mat/0110154), Alexandrov and Bratkovsky (cond-mat/0207173) argue that they
correctly took into account the chemical potential oscillations in their
analytical theory of combination frequencies in multiband low-dimensional
metals by expanding the free energy in powers of the chemical potential
oscillations. In this reply, we show that this claim contradicts their original
paper (Phys. Rev. B 63, 033105 (2001)). We demonstrate that the condition given
for the expansion is mathematically incorrect. The correct condition allows to
understand the limits of validity of the analytical theory.Comment: 4 page
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
Nonlocal correlations of the local density of states in disordered quantum Hall systems
Motivated by recent high-resolution scanning tunneling microscopy (STM)
experiments in the quantum Hall regime both on massive two-dimensional electron
gas and on graphene, we consider theoretically the disorder averaged nonlocal
correlations of the local density of states (LDoS) for electrons moving in a
smooth disordered potential in the presence of a high magnetic field. The
intersection of two quantum cyclotron rings around the two different positions
of the STM tip, correlated by the local disorder, provides peaks in the spatial
dispersion of the LDoS-LDoS correlations when the intertip distance matches the
sum of the two quantum Larmor radii. The energy dependence displays also
complex behavior: for the local LDoS-LDoS average (i.e., at coinciding tip
positions), sharp positive correlations are obtained for tip voltages near
Landau level, and weak anticorrelations otherwise.Comment: 11 pages, 8 figures ; v2: 2 references added and small extension of
conclusion, similar to published versio
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