Ronald Meisels

Circular-Polarization-Dependent Study of the Microwave Photoconductivity in a Two-Dimensional Electron System

The polarization dependence of the low field microwave photoconductivity and absorption of a two-dimensional electron system has been investigated in a quasioptical setup in which linear and any circular polarization can be produced in situ. The microwave induced resistance oscillations and the zero resistance regions are notably immune to the sense of circular polarization. This observation is discrepant with a number of proposed theories. Deviations between different polarizations occur only near the cyclotron resonance where an unprecedented large resistance response is observed.

Refraction and rightness in photonic crystals

We present a study on relation between the refraction and rightness effects in photonic crystals applied on a 2D square lattice photonic crystal. The plane wave (the band and equifrequency contour analyses) and FDTD calculations for both TM and TE modes revealed all possible refraction and rightness cases in photonic crystal structures in the first three bands. In particular, we show for the first time, a possibility of the left-handed positive refraction. This means that left-handedness does not necessarily imply negative refraction in photonic crystals.

Open quantum dots—probing the quantum to classical transition

Quantum dots provide a natural system in which to study both quantum and classical features of transport. As a closed testbed, they provide a natural system with a very rich set of eigenstates. When coupled to the environment through a pair of quantum point contacts, each of which passes several modes, the original quantum environment evolves into a set of decoherent and coherent states, which classically would compose a mixed phase space. The manner of this breakup is governed strongly by Zureks decoherence theory, and the remaining coherent states possess all the properties of his pointer states. These states are naturally studied via traditional magnetotransport at low temperatures. More recently, we have used scanning gate (conductance) microscopy to probe the nature of the coherent states, and have shown that families of states exist through the spectrum in a manner consistent with quantum Darwinism. In this review, we discuss the nature of the various states, how they are formed, and the signatures that appear in magnetotransport and general conductance studies.

Determination of the hydrogen concentration of silicon nitride layers by Fourier transform infrared spectroscopy

We report on new accurate FTIR measurements of the hydrogen content of amorphous silicon nitride (SiN) layers by evaluating the corresponding absorption lines with the help of polynomial fits. Our measurements show large differences in the hydrogen concentrations comparing layers which were deposited by plasma-enhanced chemical vapor deposition with layers deposited by thermal low-pressure chemical vapor deposition. The hydrogen content of the layers can be successfully reduced by applying various annealing procedures.

Dynamical Scaling of the Quantum Hall Plateau Transition

Using different experimental techniques, we examine the dynamical scaling of the quantum Hall plateau transition in a frequency range f=0.1-55 GHz. We present a scheme that allows for a simultaneous scaling analysis of these experiments and all other data in literature. We observe a universal scaling function with an exponent kappa=0.5+/-0.1, yielding a dynamical exponent z=0.9+/-0.2.

Negative refraction and flat-lens focusing in a 2D square-lattice photonic crystal at microwave and millimeter wave frequencies

We report on a study of the wave propagation and refraction in a 2D square-lattice photonic crystal for the first two photonic bands as well as the coupling of the external waves and criteria for flat-lens focusing. Microwave experiments and numerical simulations are performed. Main results concern the transition from positive to negative refraction below the first band gap, the flat-lens focusing using a novel criterion, viz. the constancy of the ratio of the tangents of the incident and refracted angle. Focusing results for medium ( approximately 10) and ultra-large dielectric contrast ( approximately 100) are presented. In the latter case focusing with a spot size below one wavelength at distances several wavelengths behind the photonic crystal is achieved.

Physical and materials aspects of photonic crystals for microwaves and millimetre waves

Abstract Experimental and numerical results on photonic crystals are presented for the frequency range 26–60 GHz. The material used is alumina where two techniques have been applied for fabricating the photonic crystals: manual assembly of alumina rods and rapid prototyping. The observed positions of the fundamental and higher photonic band gaps are in excellent agreement with the calculated results. A new type of defect in the 3D woodpile structure, is created by inserting interstitial rods. As a new 2D structure a square parquet lattice is investigated. The concept of a negative index of refraction is adressed including a model calculation and an experimental demonstration by the transmission through a slab of a 2D photonic crystal.

Extraordinary transmission in metal hole array-photonic crystal hybrid structures

In this work we show that structures consisting of a metal hole array (MHA) lying on top of a 2D photonic crystal (PhC) exhibit the extraordinary transmission effect. In contrast to single MHAs, the extraordinary transmission in such hybrid structures is due to the coupling of an incident wave to eigenmodes of the PhC. Thus, the spectral positions of the transmission peaks are defined by the spectral positions of the corresponding PhC eigenmodes. Our results provide a novel powerful tool to manipulate light on a subwavelength scale.

Wide band gaps and low-loss waveguiding in ceramic high dielectric constant photonic crystals

Photonic crystals based on dielectric material with very high dielectric constant e are investigated by transmission experiments in the microwave range and by calculations of the band structure and wave propagation. The material used is a tungsten-bronze-type ceramic (BaO–Nd2O3–4TiO2) with e≈90. Our results demonstrate the superior properties of such a material, including omnidirectional and complete gaps, and improved waveguiding. This type of photonic crystals opens an additional road for basic research and applications regarding electronic devices in the radio frequency and microwave ranges as well as for spectroscopic techniques in the terahertz range.

Magneto-transport in open quantum dot arrays at the transition from low to high magnetic fields: Regularity and chaos

The mixed phase space in an open quantum dot array with a soft confining potential is studied in low and high magnetic fields. Chaos occurs due to the perturbations by the constrictions connecting the dots of the array. Regular orbits and the areas of Kalmogorov-Arnold-Moser islands in phase space become increasingly dominating with increasing magnetic field. The correspondence to the high-field quantum-mechanical picture in a 2D electron system with boundaries is discussed.