Coulomb Narrowing of the Quantum Cyclotron Resonance in a Nondegenerate Two-Dimensional Electron Liquid

Abstract

We have observed a narrowing of the linear cyclotron resonance linewidth with an increase in the density of surface electrons on liquid helium in the electron-vapor atom scattering regime. The effect changes sign at densities n s . 1.7 3 10 8 cm 22 . The data are interpreted as a Coulombic effect on the Landau level width produced by a strong fluctuating electric field. [S0031-9007(99) PACS numbers: 73.20. Dx, 73.25. + i, 76.40. + b Cyclotron resonance (CR) studies in two-dimensional (2D) electron systems such as inversion layers on semiconductor surfaces and electrons bound at the free surface of liquid helium have been of great interest for many years [1,2]. Cyclotron resonance serves as a powerful probe for the effects of quantization of both out-of-plane and in-plane (orbital) motions on electron transport phenomena [3,4]. Two-dimensional electrons on a liquid helium surface are usually under extremely strong coupling conditions with respect to mutual Coulomb interaction: e 2 p pn s ͞k B T ¿ 1 (here n s is the electron density). At such conditions a strong influence of electron-electron interaction on the CR linewidth and line shape is expected. In the ultraquantum limit for short-ranged scatterers, according to [1] , the linewidth is determined by the Landau level width itself. Therefore the CR may also serve as a probe for Coulombic effects on the Landau level width.Experimental studies of the Coulomb effect on the static magnetoconductivity of surface electrons (SE) on liquid helium extensively carried out over the years [5,6] were shown to be in agreement with the theoretical concept of a quasiuniform many-electron fluctuating field E f . However, the only direct study of the many-electron effect on the CR of SE [7] showed mysteriously a density dependence of the linewidth that is opposite to the theoretical predictions [8,9], putting in question the applicability of this concept.The intriguing decrease of the CR linewidth with the electron density was predicted nearly two decades ago [8]. This effect caused by the many-electron fluctuating electric field E f is expected to be quite universal: From a theoretical point of view, it does not depend much on a particular scattering mechanism and remains valid for the Wigner solid [9]. The CR data reported by that time [4] showed a slight decrease of the CR linewidth with the increase of the holding electric field E Ќ 2pen s at low temperatures T , 0.8 K, where electrons are scattered by capillary wave quanta (ripplons). Under these conditions the electron-ripplon coupling is also dependent on E Ќ which interferes with the many-electron effect. At T ϳ 1.3 K, where the main scatterers are helium vapor atoms, the opposite behavior was reported: The linewidth increases linearly with E Ќ [4]. Later, a more detailed exploration of the low temperature regime with the electron density n s being varied independently of the holding electric field E Ќ showed no sign of the linewidth narrowing with n s for the Wigner solid phase [7]. Additionally, the onset of the ele...

Novel Radiation-Induced Magnetoresistance Oscillations in a Nondegenerate Two-Dimensional Electron System on Liquid Helium

“…3. Actually, over a range of densities n s , the many-electron effects can even lead to level narrowing, as was observed in cyclotron resonance [13]. The smearing of the oscillations in Fig.…”

“…This was shown by Dykman et al, who presented a theory for both ripplon [11] and vapor atom scattering [12]. Many-electron effects have also been observed in quantum cyclotron resonance [13].Interest in this system also stems from the proposals for quantum computing using electrons on helium [14,15]. These proposals rely on the robust control of electronic quantum states using resonant microwaves.…”

Photoresonance and conductivity of surface electrons on liquid He3

“…The reduction in electron conductivity was attributed to electron-vapor atom scattering, even though this explanation was in contradiction with results of similar quantum CR measurements [6] which display an increase in SE conductivity. Of course, the comparison with quantum CR data could be misleading because in the presence of a strong magnetic field SE conductivity is affected by the many-electron effect which can lead to a substantial narrowing of the CR [8,9].…”

Low-frequency conductivity of a nondegenerate two-dimensional electron liquid in strong magnetic fields

“…15 These results were qualitatively and quantitatively confirmed by the experiment. 16,17 The question of observing the actual dynamics or electron scattering in the electron liquid has not been addressed previously. From analogy with single-electron scattering one may expect that an insight into this dynamics can be gained from the frequency dependence of xx ().…”