Nondegenerate Electron System Research Articles

Thermoelectric Transport in a Correlated Electron System on the Surface of Liquid Helium.

We report on the direct observation of the thermoelectric transport in a nondegenerate electron system trapped on the surface of liquid helium. The microwave-induced excitation of the vertical transitions of electrons between the surface-bound states results in their lateral flow, which we were able to detect by employing a segmented electrode configuration. We show that this flow of electrons arises due to the Seebeck effect. Our experimental results are in good agreement with the theoretical calculations based on kinetic equations. This demonstrates the importance of the fast electron-electron collisions, which, in particular, leads to the violation of the Wiedemann-Franz law in this system.

Weak localization effects in a quasi-one-dimensional electron system over liquid helium

Magnetoresistance ρxx measurements are performed for a quasi-one-dimensional electron system over liquid helium in the gas-scattering region (the temperature range 1.3–2.0 K). The measurements show that, as the magnetic field increases, the magnetoresistance ρxx first decreases and then passes through a minimum and increases according to the law ρxx∼B2. It is suggested that the negative magnetoresistance observed in the experiment is caused by the weak localization effects. The results of the experiment are in qualitative agreement with the theoretical model describing the weak localization effects in a one-dimensional nondegenerate electron system.

Plasmon excitations in nondegenerate quasi-one-dimensional electron systems

The many-body dielectric formalism is applied for the laterally confined nondegenerate electron system over the liquid helium surface. The density-density response function dependent on the wave number and frequency for the multisubband quasi-one-dimensional (Q1D) system is evaluated within the random-phase approximation for arbitrary values of wave number and subband index. The spectra of both intrasubband and intersubband plasmons are obtained in the limit of small wave numbers and low temperatures. The intrasubband plasmon dispersion is almost soundlike and similar to that of intrasubband plasmons in degenerate Q1D systems and in the Q1D electron chain. The intersubband mode is optical-like with frequency close to the one-electron frequency related to the lateral parabolic confinement. Intra- and intersubband magnetoplasmon frequencies are also derived. Our results are compared with recent spectroscopic experiment.

Internal forces in nondegenerate two-dimensional electron systems

We use Monte Carlo ~MC! simulations to study the Coulomb forces that drive individual electrons in a two-dimensional normal electron fluid and a Wigner crystal. These forces have been previously shown to determine many-electron magnetoconductivity and cyclotron resonance of nondegenerate electron systems; they are also known to provide an important characteristic of the dynamics of particles that form a fluid. We have calculated the moments of the force distribution that are relevant for electron transport, which will permit a quantitative comparison of the many-electron transport theory with experiment. We have investigated the shape of the force distribution. Far tails of the distribution were analyzed by combining the method of optimal fluctuation with MC calculations, and the results were compared with direct MC results. @S0163-1829~97!05424-6#

Quantum theory of thermal noises for steady-state hot-electron transport under a strong electric field.

Current fluctuation and thermal noises of an electron system biased at finite electric field E and steady current I are studied. Owing to the separability of the motion of the center of mass of electrons from the relative motions of electrons for a parabolic band, we have derived and solved a Langevin-type equation for the fluctuating center-of-mass velocity operator \ensuremath{\delta}V^. The formulas for the current fluctuation spectrum ${\ensuremath{\Gamma}}_{\ensuremath{\Delta}I}$(\ensuremath{\omega}), the voltage fluctuation spectrum ${\ensuremath{\Gamma}}_{\ensuremath{\Delta}V}$(\ensuremath{\omega}), the diffusion coefficient ${D}_{s}$(t), and zero-frequency noise temperature ${T}_{n}$ have been derived microscopically. In particular, we obtain a generalized fluctuation-dissipation relation for the fluctuating force operator at a finite electric field and in nonequilibrium steady state. Analytical and numerical calculations of these quantities have been carried out for both degenerate and nondegenerate electron systems. While our results for a degenerate electron system may provide a better understanding of the quantum noise at extremely low lattice temperature, the essential features of our calculated diffusion coefficient and noise temperature for a nondegenerate electron system are in good agreement with those of Monte Carlo simulation.

Space-charge waves in multilayered heterostructures

Space-charge waves in multilayered heterostructures are discussed using coupled Boltzmann equations. Acoustic plasma modes are investigated with practical examples. The formulation includes both degenerate and nondegenerate electron systems; exchange and correlation effects are incorporated using a local density approximation and are shown to affect the acoustic plasma mode significantly; lattice collisions are included using the relaxation time approximation.

Undamped Cooper pairs in a non-degenerate electron system

Following the reaction matrix technique and the Kanamori approximation. a condition is obtained for the occurence of undamped Cooper pairs in a non-degenerate electron system. Its relevance to induced superconductivity in systems with artificially populated (optically pumped) bands is pointed out.