8 research outputs found
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
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
Theory of Magneto--Acoustic Transport in Modulated Quantum Hall Systems Near
Motivated by the experimental results of Willett et al [Phys.Rev. Lett., {\bf
78}, 4478 (1997)] we develop a magneto-transport theory for the response of a
two dimensional electron gas (2DEG) in the Fractional Quantum Hall Regime near
Landau level filling factor to the surface acoustic wave (SAW) in
the presence of an added periodic density modulation. We assume there exists a
Composite Fermion Fermi Surface (CF-FS) at , and we show that the
deformation of the (CF-FS) due to the density modulation can be at the origin
of the observed transport anomalies for the experimental conditions. Our
analysis is carried out particularly for the non-local case which corresponds
to the SAW experiments. We introduce a new model of a deformed CF-FS. The model
permits us to explain anomalous features of the response of the modulated 2DEG
to the SAW near namely the nonlinear wave vector dependence of the
electron conductivity, the appearance of peaks in the SAW velocity shift and
attenuation and the anisotropy of the effect, all of which originate from
contributions to the conductivity tensor due to the regions of the CF-FS which
are flattened by the applied modulation.Comment: 13 pages, 4 figures, the published versio
Dynamical Kohn Anomaly in Surface Acoustic Wave Response in Quantum Hall Systems Near
The dynamical analog of the Kohn Anomaly image of the Fermi Surface is
demonstrated for the response functions to the surface acoustic waves in
Quantum Hall Systems near . Kinks appear in the velocity shift
and attenuation coefficient . The effect is considerably
enhanced under periodic modulation and should be observable.Comment: 5 pages, 2 figures, the published versio