R. W. van der Heijden

Cyclotron resonance from the far-infrared transmission and the photoconductivity of a two-dimensional electron gas in a GaAs/AlGaAs heterojunction

Cyclotron resonance is investigated in far-infrared transmission and in photoconductivity measurements on a two-dimensional electron gas in an AlGaAs/GaAs heterojunction. The photoresistivity signal, divided by the temperature coefficient of the resistivity, displayed as a function of magnetic field, reproduces quite well the cyclotron resonance line observed in transmission. There is a slight difference in line width, which may be due to a shorter scattering time for localized as compared to non-localized electrons.

A new mechanism for high‐frequency rectification at low temperatures in point contacts between identical metals

Experimental results are reported of high‐frequency (∼ THz) radiation detection by metal‐metal point contacts at low temperatures as a function of bias voltage. The dominant detection mechanism can be attributed to rectification due to electron‐phonon‐scattering‐induced nonlinearity of the I‐V characteristics, a process not observed before.

Tunable narrow‐linewidth oscillations and current‐voltage characteristics of a resistive dc SQUID

The output voltage of a dc superconducting quantum interference device (SQUID) containing a resistive section Rs oscillates at a frequency νq =Vs/ φ0 (φ0=flux quantum) when a current controlled voltage Vs is maintained across Rs. These oscillations have been observed from ∼10−1 to 1011 Hz, using Rs values ranging from ∼10−10 to ∼10−3 Ω in low inductance (∼10−10 H) point contact SQUID loops. At high frequencies, they manifest themselves in the dc current‐voltage characteristics by inducing extra current steps.

Experimental investigation of ghostlines in Fourier spectroscopy in the far-infrared

Abstract In this work we have investigated the intensity of ghostlines which occur in the spectrum obtained with a two-beam Fourier interferometer when the travel of its moving mirror is periodically distorted. This intensity has been compared quantitatively with the amplitude of the periodic travel distortion as measured directly with a dilatometer, enabling the determination of travel distortions as small as 0.2 μm. It is concluded that the amplitude of the periodic distortion as calculated from the measured intensity of the ghostlines is in fair agreement with the distortion as obtained from a direct measurement.

Contribution of the spreading resistance to high‐frequency rectification in metal‐metal point contacts

High‐frequency radiation detection by metal‐metal point contacts is investigated as a function of bias voltage at far‐infrared frequencies. Detection occurs through rectification due to a nonlinearity of the current‐voltage characteristic. The relative contribution to the rectification due to an electron phonon scattering mechanism occurring in the bulk material (‘‘spreading resistance’’) is compared with other mechanisms. The spreading resistance nonlinearity was identified by measurements at liquid helium temperatures. For low contact resistances (≲50 Ω) this nonlinearity was generally dominant, for higher resistances it may occur in addition to and independently of the other mechanisms.

Photon assisted tunneling in superconductor-normal metal point contacts at far-infrared frequencies

Abstract The response of normal metal-superconductor point contacts to radiation at frequencies up to 2.5 THz is studied experimentally. The results can be analyzed in terms of the so called Photon Assisted Tunneling (PAT) effect and are in excellent agreement with recent theoretical predictions.

Far-infrared investigations of magnetoplasma effects in Bi in quantizing magnetic fields

Abstract A comprehensive experimental study is made of the magneto-optic absorption of Bi in the Voigt configuration in quantizing magnetic fields at frequencies covering the far-infrared range. At these frequencies, the typical magnetoplasma absorption features (cyclotron resonances, hybrid resonances and dielectric anomalies) gradually change character due to the strong quantization of the charge carrier system and because the experimental- and cyclotron frequency become comparable to - and finally exceed - the plasma frequency. The fundamental quantum cyclotron resonance lineshape becomes strongly affected by transitions with k B ≠ 0 ( k B momentum along magnetic field), due to the nonparabolic band structure. Effects of carrier redistribution over different carrier pockets in the quantizing field region are strongly reflected in the hybrid resonance and dielectric anomaly lineshapes. In order to analyze the data, the absorption spectra are calculated in the limit of local electrodynamics, using either a convensional classical method or more appropriate quantum-mechanical model. The latter model accounts qualitatively well for all major effects observed experimentally, taking into account the proper expression for the velocity matrix element for a nonparabolic band of the two-band model, over the entire frequency range. Nonlocal effects, clearly seen in the experimental data, are discussed qualitatively; these effects are illustrated by some additional experimental results obtained for Sb where nonlocal effects are very pronounced and strong.

Hall‐effect determination of the N‐trap bound state in GaAs1−xPx

Hall‐effect measurements as a function of temperature on nitrogen‐containing GaAs1−xPx have shown that the nitrogen isoelectronic trap in these materials can be best described by a bound state in the band gap, occupied by electrons according to the equilibrium thermal distribution. It is shown that the presence of nitrogen can have a pronounced effect on the free‐carrier density. Our results are in excellent agreement with recent optical data.

Differential heterodyne frequency conversion at 0.4 mm wavelength

A Josephson‐effect differential heterodyne receiver converts a variable signal frequency fS, near a fixed local oscillator fL, to a fixed intermediate frequency fI=fS−fL−fQ, by mixing between fD=fS−fL and a voltage‐tunable variable quantum oscillation fQ=2eV/h provided by a double‐junction resistive interferometer. At fL−0.7 THz provided by a far infrared formic acid laser, with fS=fL+fD provided by a Doppler shift, power conversion efficienciesηQ from fDγfI up to 0.2 were observed. Linewidths of the quantum oscillation δfQ∠ (2kBT/πL)1/2 (2eR/h) down to ∠0.5 Hz were observed for R=3.3×10−9Ω interferometer resistance, and L∠10−9 H interferometer inductance, demonstrating an intrinsic frequency resolution of 1 in 1012 at high conversion efficiency for the technique.

Direct heterodyne detection of 245‐GHz radiation using the internal narrowband oscillations of a resistive dc SQUID

A current controlled voltage across a resistive section in a double Josephson junction interferometer (dc resistive superconducting quantum interference device) maintains a difference voltage between the junctions to generate a narrowband oscillatory signal at the beat frequency νq of the individual junction frequencies. This internal oscillation was used to directly down‐convert a signal at 246 GHz to a very low (<1 MHz) intermediate frequency.