40 research outputs found
Quantum Oscillations of Elastic Moduli and Softening of Phonon Modes in Metals
In this paper we present a theoretical analysis of the effect of
magnetostriction on quantum oscillations of elastic constants in metals under
strong magnetic fields.
It is shown that at low temperatures a significant softening of some acoustic
modes could occur near peaks of quantum oscillations of the electron density of
states (DOS) at the Fermi surface (FS). This effect is caused by a magnetic
instability of a special kind, and it can give rise to a lattice instability.
We also show that the most favorable conditions for this instability to be
revealed occur in metals whose Fermi surfaces include nearly cylindrical
segments.Comment: 5 pages, 1 figur
Fermi-liquid theory of the surface impedance of a metal in a normal magnetic field
In this paper we present detailed theoretical analysis of the frequency
and/or magnetic field dependence of the surface impedance of a metal at the
anomalous skin effect. We calculate the surface impedance in the presence of a
magnetic field directed along the normal to the metal surface. The effects of
the Fermi-liquid interactions on the surface impedance are studied. It is shown
that the cyclotron resonance in a normal magnetic field may be revealed {\it
only and exclusively} in such metals whose Fermi surfaces include segments
where its Gaussian curvature turns zero. The results could be applied to
extract extra informations concerning local anomalies in the Fermi surface
curvature in conventional and quasi-two-dimensional metals.Comment: 10 pages, 1 figure, text added and rearranged, computational details
are moved into Appendice
Deformed Fermi Surface Theory of Magneto-Acoustic Anomaly in Modulated Quantum Hall Systems Near
We introduce a new generic model of a deformed Composite Fermion-Fermi
Surface (CF-FS) for the Fractional Quantum Hall Effect near in the
presence of a periodic density modulation. Our model permits us to explain
recent Surface Acoustic Wave observations of anisotropic anomalies [1,2] in
sound velocity and attenuation- appearance of peaks and anisotropy - which
originate from contributions to the conductivity tensor due to regions of the
CF-FS which are flattened by the applied modulation. The calculated magnetic
field and wave vector dependence of the CF conductivity,velocity shift and
attenuation agree with experiments.Comment: Revised manuscript (cond-mat/9807044) 23 September 1998; 10 page
Inelastic electron transport in polymer nanofibers
In this paper we present theoretical analysis of the electron transport in
conducting polymers. We concentrate on the study of the effects of temperature
on characteristics of the transport. We treat a conducting polymers in a metal
state as a network of metallic-like grains connected by electron quantum
tunneling via intermediate state localized on a polymer chain between the
grains. To analyze the effects of temperature on this kind of electron
intergrain transport we represent the thermal environment as a phonon bath
coupled to the intermediate state. The electron transmission is computed using
the Buttiker model within the scattering matrix formalism. This approach is
further developed, and the dephasing parameter is expessed in terms of relevant
energies including the thermal energy. It is shown that temperature
dependencies of both current and conductance associated with the above
transport mechanism differ from those typical for other conduction mechanisms
in conducting polymers. This could be useful to separate out the contribution
from the intergrain electron tunneling to the net electric current in transport
experiments on various polymer nanofibers. The proposed model could be used to
analyze inelastic electron transport through molecular junctions.Comment: 8 pages, 5 pictures; text added, figures adde
Fermi-liquid and Fermi surface geometry effects in propagation of low frequency electromagnetic waves through thin metal films
In the present work we theoretically analyze the contribution from a
transverse Fermi-liquid collective mode to the transmission of electromagnetic
waves through a thin film of a clean metal in the presence of a strong external
magnetic field. We show that at the appropriate Fermi surface geometry the
transverse Fermi-liquid wave may appear in conduction electrons liquid at
frequencies significantly smaller than the cyclotron frequency of
charge carriers provided that the mean collision frequency
is smaller than Also, we show that in realistic metals size
oscillations in the transmission coefficient associated with the Firmi-liquid
mode may be observable in experiments. Under certain conditions these
oscillations may predominate over the remaining size effects in the
transmission coefficient.Comment: 9 pages, 5 figures, text adde
Local Geometry of the Fermi Surface and Magnetoacoustic Responce of Two-Dimensional Electron Systems in Strong Magnetic Fields
A semiclassical theory for magnetotrasport in a quantum Hall system near
filling factor based on the Composite Fermions physical picture is
used to analyze the effect of local flattening of the Composite Fermion Fermi
surface (CF-FS) upon magnetoacoustic oscllations. We report on calculations of
the velocity shift and attenuation of a surface acoustic wave (SAW) which
travels above the two-dimensional electron system, and we show that local
geometry of the CF-FS could give rise to noticeable changes in the magnitude
and phase of the oscillations. We predict these changes to be revealed in
experiments, and to be used in further studies of the shape and symmetries of
the CF-FS. Main conclusions reported here could be applied to analyze
magnetotransport in quantum Hall systems at higher filling factors provided the Fermi-liquid-like state of the system.Comment: 7 pages, 2 figure
On the Theory of Quantum Oscillations of the Elastic Moduli in Layered Conductors
In this paper we study theoretically how the local geometry of the Fermi
surface (FS) of a layered conductor can affect quantum oscillations in the
thermodynamic observables. We introduce a concrete model of the FS of a layered
conductor. The model permits us to analyze the characteristic features of
quantum oscillatory phenomena in these materials which occure due to local
anomalies of the Gaussian curvature of the FS. Our analysis takes into account
strong interaction among quasiparticles and we study the effect of this
interaction within the framework of Fermi-liquid theory. We show that the
Fermi-liquid interaction strongly affects the density of states of
quasiparticles (DOS) on the FS. As a result DOS can have singularities near the
peaks of its oscillations in a strong magnetic field. These singularities can
be significantly strengthened when the FS of the layered conductor is locally
flattened. This can lead to magnetic and lattice instabilities of a special
kind which are considered in the final part of the work.Comment: 11 pages, 2 figures, minor changes in the title are made, published
versio
Acoustic Cyclotron Resonance and Giant High Frequency Magnetoacoustic Oscillations in Metals with Locally Flattened Fermi Surface
We consider the effect of local flattening on the Fermi surface (FS) of a
metal upon geometric oscillations of the velocity and attenuation of ultrasonic
waves in the neighborhood of the acoustic cyclotron resonance. It is shown that
such peculiarities of the local geometry of the FS can lead to a significant
enhancement of both cyclotron resonance and geometric oscillations.
Characteristic features of the coupling of ultrasound to shortwave cyclotron
waves arising due to the local flattening of the FS are analyzed.
PACS numbers 71.18.+y; 72.15.Gd; 72.15.-vComment: 8 pages, 3 figures, text revise