Far-infrared induced current in a ballistic channel -- potential barrier structure

We consider electron transport in a ballistic multi-mode channel structure in the presence of a transversely polarized far-infrared (FIR) field. The channel structure consists of a long resonance region connected to an adiabatic widening with a potential barrier at the end. At frequencies that match the mode energy separation in the resonance region we find distinct peaks in the photocurrent, caused by Rabi oscillations in the mode population. For an experimental situation in which the width of the channel is tunable via gates, we propose a method for reconstructing the spectrum of propagating modes, without having to use a tunable FIR source. With this method the change in the spectrum as the gate voltage is varied can be monitored.Comment: Submitted to Phys. Rev.

Coherent quantum transport in narrow constrictions in the presence of a finite-range longitudinally polarized time-dependent field

We have studied the quantum transport in a narrow constriction acted upon by a finite-range longitudinally polarized time-dependent electric field. The electric field induces coherent inelastic scatterings which involve both intra-subband and inter-sideband transitions. Subsequently, the dc conductance G is found to exhibit suppressed features. These features are recognized as the quasi-bound-state (QBS) features which are associated with electrons making transitions to the vicinity of a subband bottom, of which the density of states is singular. Having valley-like instead of dip-like structures, these QBS features are different from the G characteristics for constrictions acted upon by a finite-range time-modulated potential. In addition, the subband bottoms in the time-dependent electric field region are shifted upward by an energy proportional to the square of the electric field and inversely proportional to the square of the frequency. This effective potential barrier is originated from the square of the vector potential and it leads to the interesting field-sensitive QBS features. An experimental set-up is proposed for the observation of these features.Comment: 8 pages, 4 figure

Coherent Far-Infrared Mode Pumping in Ballistic Electron Channels

The influence of a high frequency electromagnetic field on transport properties of ballistic electron channels is investigated theoretically. We are primarily concerned with submicron-width channels formed by split-gate depletion of a two-dimensional electron gas at a GaAs/AlGaAs heterostructure interface. The pronounced quantization in the transverse direction of such channels opens the possibility to manipulate propagating electrons by inducing transitions between transverse modes by means of electromagnetic fields. Our investigations are focused on resonant mode coupling effects in long channels, induced by monochromatic far-infrared (FIR) fields polarized in the transverse direction of the channel. Within a single-particle transmission approach we predict the developing of spatial oscillations in the population of transverse modes, on a length scale much longer than the de Broglie wavelength. These oscillations have their correspondence in Rabi oscillations in atomic and molecular beams and in many other phenomena which exploit the resonant behavior of a two-level system. Different arrangements for detecting and exploiting this non-equilibrium situation are examined. A constriction in the channel leads to a retardation and a possibility for reflection of excited modes, while a widening leads to an acceleration and a possibility for excited modes to pass potential barriers. Such mechanisms affect the transmission probability and therefore lead to a change in the conductance. Also photovoltaic effects are found which eliminates the need for an external power supply. In the long run one can imagine to exploit this pumping mechanism in applications such as tunable narrow-band detectors and frequency demodulators, or even in transistors to which both the power and clock is distributed globally from the FIR field

Coherent Far-Infrared Mode Pumping in Ballistic Electron Channels

The influence of a high frequency electromagnetic field on transport properties of ballistic electron channels is investigated theoretically. We are primarily concerned with submicron-width channels formed by split-gate depletion of a two-dimensional electron gas at a GaAs/AlGaAs heterostructure interface. The pronounced quantization in the transverse direction of such channels opens the possibility to manipulate propagating electrons by inducing transitions between transverse modes by means of electromagnetic fields. Our investigations are focused on resonant mode coupling effects in long channels, induced by monochromatic far-infrared (FIR) fields polarized in the transverse direction of the channel. Within a single-particle transmission approach we predict the developing of spatial oscillations in the population of transverse modes, on a length scale much longer than the de Broglie wavelength. These oscillations have their correspondence in Rabi oscillations in atomic and molecular beams and in many other phenomena which exploit the resonant behavior of a two-level system. Different arrangements for detecting and exploiting this non-equilibrium situation are examined. A constriction in the channel leads to a retardation and a possibility for reflection of excited modes, while a widening leads to an acceleration and a possibility for excited modes to pass potential barriers. Such mechanisms affect the transmission probability and therefore lead to a change in the conductance. Also photovoltaic effects are found which eliminates the need for an external power supply. In the long run one can imagine to exploit this pumping mechanism in applications such as tunable narrow-band detectors and frequency demodulators, or even in transistors to which both the power and clock is distributed globally from the FIR field

Electronically scanning beamformers based on ferroelectric technology

Basic properties and the potential of ferroelectrics for applications in electronically scanned beamformers are discussed. Low drive power consumption, relatively low losses, high speed, and the possibilities of realisation cost effective beamformers are the main advantages offered by ferroelectric technology. A brief review of ferroelectric scanning antennas is also given

Ferroelectric lens

A lens (300, 500) is disclosed for steering the exit direction (Ω) of an incident electromagnetic wave. The lens comprises a main body (210, 510) of a ferroelectric material with a first main surface (207, 507) and a first transformer (220, 222). The electromagnetic wave enters and exits the lens through the transformer, and the lens comprises means (370, 380) for creating a DC-field in a first direction in the main body. The main body (210, 510) of ferroelectric material comprises a plurality (21011-210NN, 51011-510NN) of slabs of the ferroelectric material, each slab also comprising a first (403, 603) and a second electrode of a conducting material. The means for creating a DC-field can create a gradient DC-field in the first direction using the first and second electrodes, so that the dielectric constant in the main body will also be a gradient in the first direction, thus enabling steering of the existing electromagnetic wav

Ferroelectric lens

A lens (300, 500) is disclosed for steering the exit direction (Ω) of an incident electromagnetic wave. The lens comprises a main body (210, 510) of a ferroelectric material with a first main surface (207, 507) and a first transformer (220, 222). The electromagnetic wave enters and exits the lens through the transformer, and the lens comprises means (370, 380) for creating a DC-field in a first direction in the main body. The main body (210, 510) of ferroelectric material comprises a plurality (21011-210NN, 51011-510NN) of slabs of the ferroelectric material, each slab also comprising a first (403, 603) and a second electrode of a conducting material. The means for creating a DC-field can create a gradient DC-field in the first direction using the first and second electrodes, so that the dielectric constant in the main body will also be a gradient in the first direction, thus enabling steering of the existing electromagnetic wav

Ferroelectric lens

A lens (300, 500) is disclosed for steering the exit direction (Ω) of an incident electromagnetic wave. The lens comprises a main body (210, 510) of a ferroelectric material with a first main surface (207, 507) and a first transformer (220, 222). The electromagnetic wave enters and exits the lens through the transformer, and the lens comprises means (370, 380) for creating a DC-field in a first direction in the main body. The main body (210, 510) of ferroelectric material comprises a plurality (21011-210NN, 51011-510NN) of slabs of the ferroelectric material, each slab also comprising a first (403, 603) and a second electrode of a conducting material. The means for creating a DC-field can create a gradient DC-field in the first direction using the first and second electrodes, so that the dielectric constant in the main body will also be a gradient in the first direction, thus enabling steering of the existing electromagnetic wav