Pkh Sommerfeld

Single wire configuration of electrons on a suspended helium film

A new technique to create and measure a single wire arrangement of electrons on helium is presented. Experimental results are reported for a 300 μm wide, 12 mm long channel.

Mobile electrons on a helium film supported by capillary action

A thick film of liquid 4He is suspended by the effect of capillary action on an array of small discs. A two-dimensional electron system (2DES) has been realized on this film. Using standard low-frequency impedance measurements it could be established that the electrons remain mobile when passing from the regime of a bulk liquid to a suspended film. Using these techniques allows the investigation of a new class of low-dimensional electron systems.

The effect of confining electric fields on new magnetoplasma excitations in a 2D electron system

The effects of spatially varying electrostatic holding fields on several new types of edge excitations in a magnetic field are investigated for the 2DES on liquid helium. They clearly show that (a) the modes are localized near inhomogeneity boundaries of the sample and (b) different, independent edge modes exist.

Interedge magnetoplasmons as a probe for the Wigner crystal

Linewidth measurements of Interedge Magnetoplasmon resonances in a 2-dimensional electron system on liquid helium atB=1 T are reported. They exhibit a fairly abrupt linewidth broadening near the crystallization temperature.

Low-frequency edge magnetoplasmons in a ring-shaped two-dimensional electron gas on liquid helium

Abstract A ring-shaped two-dimensional electron gas on the surface of liquid helium is created by electrostatic confinement. The very low-frequency response to a capacitively coupled driving field is investigated in strong magnetic fields. It is found that an edge magnetoplasmon exists both at the outside edge and at the inside edge of the ring. The two modes propagate in opposite directions.

Observation of harmonic, high-field, low-frequency edge-magnetoplasma resonances for electrons on helium

Abstract Results are reported of experiments on resonant edge-magnetoplasma modes in a two-dimensional electron fluid on liquid helium in the temperature range 0.1K T B -2 (τ is the zero-field scattering time). Preliminary measurements suggest a minimum in the resonant linewidth as a function of temperature.

Hall magnetocapacitance in two-dimensional electron systems

The magnetocapacitance of a two-dimensional electron system (2DES) is investigated experimentally, both under the and away from quantum Hall conditions, at frequencies between 1 kHz and 100 MHz. The nature of the capacitive signal in a bounded 2DES is determined by a resistive cutoff frequency 1/t?sxx, the longitudinal magnetoconductivity. A new response mechanism is reported for angular frequencies ?>1/t, which is controlled by the transverse or Hall conductivity sxy and the boundaries of the sample. The mechanism is also found at frequencies far below those of the edge magnetoplasma resonances and away from the quantum Hall regime.

The carrier mobility in a quasi-one-dimensional electron system over liquid helium

The mobility of carriers in a quasi-one-dimensional electron system over liquid helium has been measured at temperatures of 0.5–1.5 K in pressing electric fields up to 2.5 kV/cm. The system is realized with using the optical diffraction grating situated at heightH over liquid helium level. It is shown that electron mobility is dependent on the valueH and significantly lower than that of over bulk helium. The mobility increases under lowering temperature and then decreases passing maximum. The behavior of the mobility is attributed with the localization of electrons in a quasi-one-dimensional system.

Collective Excitations in High Magnetic Fields

The properties of a two-dimensional electron system (2DES) are drastically modified by a magnetic field applied perpendicular to the plane of the 2DES. The effects may be classified into those that affect the single-electron properties of the system, i.e. magnetoconductivity, and those affecting the collective excitations, i.e. the magnetoplasma oscillations. The experimental work on magnetoconductivity is presented in the chapter by Lea, while the theoretical aspects are treated in the chapters by Dykman and by Monarkha. The present chapter deals with collective excitations.

Magnetic field dependence of the high-frequency capacitive response of a 2-dimensional electron gas in the quantum hall regime

The rf-transmission between two antennas coupling capacitively to a 2-dimensional electron gas at a GaAs-AlGaAs heterojunction is investigated as a function of magnetic field <6 T and frequency <600 MHz at a temperatureT∼1.5 K. It is found that the coupling between the antennas terminates at the frequency of an edge magnetoplasma resonance, both on and outside the Quantum Hall plateaus.