Local geometry of the Fermi surface and magnetoacoustic response of two-dimensional electron systems in strong magnetic fields

Abstract

A semiclassical theory for magnetotrasport in a quantum Hall system near filling factor ν = 1/2 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 ν = 3/2, 5/2 provided the Fermi-liquid-like state of the system.

Local flattening of the Fermi surface and quantum oscillations in the magnetoacoustic response of a metal

“…It is likely that FSs of some metals include locally flattened segments. Even slight distortion of a Fermi sphere due to the effect of crystalline fields results in the FS flattening at some points [4]. There is an experimental evidence that points of flattening exist on the FSs of cadmium, zinc and potassium [5,6,7].…”

Local geometry of the Fermi surface and quantum oscillations in the linear response of metals

“…Likewise, the flattening points at the FS may give rise to some anomalies in the magnetoacoustic response of a two-dimensional electron gas, as shown in the papers [9,10].…”

“…This is typical for all effects arising due to local peculiarities in the FS geometry. For instance, the angular dependence of the amplitudes of magnetoacoustic commensurability oscillations in a two-dimensional electron system was discussed in [10]. In the present work we analyse the angular dependences of quantum oscillation magnitudes for different kinds of local anomalies of the FS curvature.…”

“…This is typical for all effects arising due to local peculiarities in the FS geometry. For instance, angular dependence of the amplitudes of magnetoacoustic commensurability oscillations in a twodimensional electron system was discussed in Ref [10].…”

“…It has been shown that when the FS includes points or lines where at least one of the principal radii of curvature becomes infinitely large, then changes may be observed in the frequency and temperature dependences of sound dispersion and absorption [2][3][4][5][6], and in the frequency dependence of the surface impedance of a conventional metal under the anomalous skin effect [7,8]. Likewise, the flattening points at the FS may give rise to some anomalies in the magnetoacoustic response of a two-dimensional electron gas, as shown in [9,10].…”