Adir M. Luiz

Radiofrequency generation using a SNS microbridge

The feasibility of a sinusoidal oscillator is demonstrated using a SNS microbridge linked with a series RLC tank circuit, supplied by a constant DC current, and operated at the negative differential resistance range of its I-V characteristic curve. The frequency of this sinusoidal generator is equal to the resonant frequency of the tank RLC circuit. This type of generator can be operated for a wide range of frequencies, from audio frequencies up to the limit of microwaves. Other possible electronic applications based on the appropriate use of the negative resistance region of the I-V characteristic curve of the SNS microbridge are suggested.

Microwave Generation using a SNS Junction

It has been shown recently that the current-voltage characteristic of a metallic (non-tunneling) Josephson junction could exhibit a negative differential resistance at low voltages, as a predictable and reproducible effect. This letter shows an alternative procedure to generate non-Josephson microwaves (in the cm and mm range) taking advantage of this effect. It is shown that, instead of obtaining harmonic oscillations with the AC Josephson effect, it is possible to generate microwaves using the averaged IVC (current-voltage characteristics) of a SNS junction (a Josephson junction which exhibits no tunneling and has no hysteresis in the IVC).

Heterodyne mixer using superconductor-normal metal-superconductor junction

Abstract We propose a design for a millimeter-wave-radio-astronomy heterodyne mixer using a superconductor-normal metal-superconductor junction device as the mixer. We simulate its current-voltage characteristics as a function of its relevant physical parameters, we use its non-linearity for mixing frequencies and its negative derivative to calculate the conversion gain. As the radiofrequency sensor is a SQUID, the whole system should be operated at low temperature, below the superconducting transition at Tc, avoiding any thermal interface.

Superconducting negative resistance switches

A new type of superconducting switch using the negative differential resistance of the CVC (current-voltage characteristic) curve of a nontunneling Josephson junction is suggested. With the proper choice of the load resistor monostable or bistable switching circuits may be designed. The power consumption, the switching speed and other relevant characteristic features of the proposed superconducting switches are analyzed.

Superconductor-normal metal-superconductor junctions for signal amplification and harmonic multiplication

We report signal amplification and harmonic multiplication processes based on the nonlinear current-voltage characteristics (CVC) displayed by superconductor-normal metal-superconductor (SNS) junctions. Such junctions may exhibit a negative differential resistance at low voltages, the so called low-voltage-negative-differential-resistance (LVNDR) effect. This effect is due to the quantum mechanical multiple Andreev reflection mechanism in very clean systems and is stable against a bias voltage. Therefore, it is in principle possible to use these junctions as an active element in a variety of circuit applications such as oscillators, amplifiers or mixers, in the microwave and millimeter-wave range.

A proposal to introduce a topic of contemporary physics into high-school teaching

This article presents an approach to integrate contemporary physics into high-school teaching. We present a simple way to understand mass spectroscopy using basic physics concepts, so that high-school students may have contact with recent topics of modern research. The main features of a time-of-flight (TOF) mass spectrometer using secondary school physics concepts are discussed. The use of home-made apparatus is described. Some results obtained with CsI samples showing the dependence between mass and TOF are presented.

Fitting experimental current-voltage data using a simplified model for SNS junctions

Abstract We used a microscopic theory for superconductor-normal metal-superconductor junction (SNS) junction in a simplified model and experimental data from the literature for calculating the current-voltage characteristics (CVC) of some junctions. The comparison with experimental curves shows that this simple model may be successfully used to fit the experimental CVC of SNS junctions of either low Tc or high Tc superconductors.

Microbridges and point contacts as negative differential resistance devices in the conventional generation of microwaves, up to the sub-millimeter range

Abstract A recent theory on superconductor-normal metal-superconductor systems has shown that the superconducting microbridges and point contacts may have negative differential resistance in their current-voltage characteristics. These microbridges and point contacts can act as negative resistance devices for generating harmonic oscillations in conventional circuitry, up to the sub-millimeter limit. The expected power output is of the order of a microwatt.

A simple model to estimate the optimal doping of p - Type oxide superconductors

Oxygen doping of superconductors is discussed. Doping high-Tc superconductors with oxygen seems to be more efficient than other doping procedures. Using the assumption of double valence fluctuations, we present a simple model to estimate the optimal doping of p-type oxide superconductors. The experimental values of oxygen content for optimal doping of the most important p-type oxide superconductors can be accounted for adequately using this simple model. We expect that our simple model will encourage further experimental and theoretical researches in superconducting materials.

Hysteretic behavior of signal amplification using SNS junctions

Abstract A superconductor–normal metal–superconductor junction (SNS junction) has a nonlinear current–voltage characteristic (CVC) that may exhibit the low-voltage negative differential resistance (LVNDR) effect. Taking advantage of this remarkable effect it may be possible to associate a SNS junction to conventional electronic circuits in order to design devices such as oscillators, amplifiers and mixers. This work simulates the output signal of an amplifier device, which is essentially a SNS junction connected with an adjustable DC voltage supplier, and an AC signal source, which could be a SNS junction as well. Sometimes the LVNDR effect is hidden under a low-voltage hysteresis on the CVC because the experiment has been performed in a current-bias measuring setup. We focus on the question of this hysteretic behavior and discuss the performance of the proposed device with and without hysteresis.