KAROL I. WYSOKIŃSKI

M. Curie-Sklodowska University
Institute of Physics, Lublin, Poland
e-mail: karol@tytan.umcs.lublin.pl

QUANTUM HALL EFFECT: THE FUNDAMENTALS

The basic understanding of the physics behind and the reasons for very high precision of the resistivity ρ_xy quantisation in integer quantum Hall effect (IQHE) and the application of the effect in metrology to define a quantum resistance standard will be briefly discussed. We also mention some recent proposals concerning the application of the quantum Hall device as an efficient qubit for future quantum computers and end up with few remarks about the contribution of single electron devices to the realisation of standards and quantum metrology which seeks the ways to beat the accuracy of classic measurements.

Keywords: quantum Hall effect, resistance standard, quantum metrology, precision measurements

Full paper (228kB): M&MS_2006_113.pdf

JAN STANKOWSKI

Polish Academy of Sciences
Institute of Molecular Physics, Poznan, Poland
e-mail: Jan.Stankowski@ifmpan.poznan.pl

MICROWAVE ABSORPTION (MMMA) - A CONTACLESS METHOD TO STUDY SUPERCONDUCTORS AND MAGNETIC NANOSTRUCTURES

Magnetically Modulated Microwave Absorption (MMMA) is a sensitive differential method to study magnetoresistence related to the voltage fluctuation in nonhomogeneous superconducting systems with Josephson junctions (JS) and in magnetic systems exhibiting giant magnetoresistence (GMR). The MMMA method has been successfully established after the discovery of polycrystalline high temperature superconductors with high concentration of Josephson junctions. MMMA proved to be the third method besides resistivity and magnetic susceptibility measurements to determine critical temperature T_c. In magnetic nanostructures MMMA enables to determine GMR(H) and magnetization reversal.

Keywords: Josephson junction, microwave absorption, HTC nanostructure

Full paper (424kB): M&MS_2006_125.pdf

J. GUTEK¹, S. WINIARZ¹, I. PIECHOCKA¹, P. PŁOTKA², R. CZAJKA<sup>1

1</sup>Poznań University of Technology
Faculty of Technical Physics, Institute of Physics, Poland
e-mail: czajka@phys.put.poznan.pl
²Institute for Semiconductor Research, Sendai, Japan

INVESTIGATIONS OF THE COULOMB BLOCKADE EFFECT IN DOUBLE TUNNEL JUNCTIONS

The Coulomb Blockade effect (CBE) is observed in double tunnel junctions where a small metallic cluster is precisely located between two outer electrodes. This electrically isolated nanocluster exhibits capacitances of attofarads. Such extremely small capacitance may cause that the charging energy E_C = e²/2C which an individual electron needs to be placed at the cluster may be bigger than the electron's thermal energy k_BT. The Coulomb potential of the electron localized at the cluster keeps the other electrons from flowing through the tunnel junction. Tunnel current increase is possible only after a discrete increase of bias voltage, what is observed as a so called Coulomb staircase in I-V curves. In our investigations, we have created an ultra-thin oxide (barrier) layer on the Si(111) 7×7 surface via controlled oxidation process inside the UHV chamber. One of the tunnel junctions was made by deposition of Ag nanoclusters onto an oxidized Si(111) surface. The other tunnel junction was set up by STM tip and vacuum when the tip was hovering over the Ag cluster. I-V curves measured in above clusters showed a step-like shape. The steps were smeared due to thermal broadening and asymmetry in capacitances and resistances of both tunnel junctions. The junction parameters were estimated by fitting the experimental curve to the theoretical one.

Keywords: Coulomb blockade, Coulomb staircase, clusters, double tunnel junction, STM

Full paper (638kB): M&MS_2006_137.pdf

ALBIN CZUBLA¹, JANUSZ KONOPKA¹, JERZY NAWROCKI<sup>2

1</sup>Central Office of Measures (GUM), Electrical Metrology Division, Time and Frequency Laboratory
Warsaw, Poland, e-mail: timegum@gum.gov.pl
²Astrogeodynamical Observatory at Borowiec (AOS), Time and Frequency Laboratory
Kórnik/k Poznania, Poland, e-mail: j.nawrocki@cbk.poznan.pl

REALIZATION OF ATOMIC SI SECOND DEFINITION IN THE CONTEXT OF UTC(PL) AND TA(PL)

In this paper, the problem of practical realization of atomic SI second definition is discussed from the metrological point of view. Special attention is devoted to the maintenance of UTC(PL) - Polish local physical realization of UTC, and to the determination of TA(PL) - the Polish independent atomic timescale. The role of such timescales , as well as local and international cooperation in time and frequency metrology is also considered. We share some Polish experience in this field.

Keywords: time and frequency metrology, timescale, UTC(PL), TA(PL), second unit

Full paper (228kB): M&MS_2006_149.pdf

MACIEJ WAWRZYNIAK

Poznan University of Technology
Institute of Electronics and Telecommunications, Poland
e-mail: mwawrz@et.put.poznan.pl

ANALOG-TO-DIGITAL CONVERTER DIFFERENTIAL NONLINEARITY ERROR CORRECTION IN BUILDING CONDUCTANCE HISTOGRAMS

In nanowire electrical conductance quantization studies, conductance histograms are built from a large number of conductance curves of conductance stepwise variations in time. The conductance curves are obtained by means of a digital oscilloscope; as each digital oscilloscope has an analog-to-digital converter (ADC) whose differential nonlinearity (DNL) error strongly affects the obtained conductance histograms. The effect of the DNL error can be corrected through the procedure described in this paper. Moreover, measurement results of the DNL error for three digital oscilloscope models and the long-term DNL error variations for one oscilloscope model are presented.

Keywords: differential nonlinearity, analog digital conversion, electrical conductance, quantized conductance, nanowires

Full paper (367kB): M&MS_2006_161.pdf

WALDEMAR NAWROCKI

Poznan University of Technology
Institute of Electronics and Telecommunications, Poland
e-mail: nawrocki@et.put.poznan.pl

REVISING THE SI: THE JOULE TO REPLACE THE KELVIN AS A BASE UNIT

The joule is proposed to replace the kelvin in the set of SI base units. Arguments in favour of such replacement are presented, including improved standard accuracy and unit system coherence. The joule is also proposed to be added to the quantum metrological triangle (which couples the volt, the ampere and the hertz) to transform it into a system called quantum metrological pyramid, that would couple four units rather than three, and allow comparison of the respective standards.

Keywords: International System of Units, quantum standards, quantum metrological pyramid

Full paper (728kB): M&MS_2006_171.pdf

B. SUSŁA¹, M. WAWRZYNIAK², J. BARNAŚ^3,4, W. NAWROCKI<sup>2

1</sup>Poznań University of Technology, Institute of Physics, Poland, e-mail: Susla@phys.put.poznan.pl
²Poznań University of Technology, Institute of Electronics and Telecommunications, Poland
³Adam Mickiewicz University, Department of Physics, Poznań, Poland
⁴Polish Academy of Sciences, Institute of Molecular Physics, Poznań, Poland

CONDUCTANCE QUANTIZATION IN FERROMAGNETIC CO NANOWIRES

Room temperature electronic transport properties of ferromagnetic quantum wires have not been yet fully understood, and the role of electronic structure of magnetic atoms in the conductance quantization is still under discussion. We present experimental results on conductance quantization in point contacts between ferromagnetic (Co) or nonmagnetic (Au) wires and semiconductor (Ge) samples. The main features of the conductance histograms are consistent with the conductance quantization in the units of quantum conductance G₀ for the nonmagnetic wires and nG₀ for the ferromagnetic Co nanowires. Such behavior of the conductance of ferromagnetic wires is a consequence of the complex electronic structure of magnetic 3d transition-metal atoms. A description of the quantization phenomena is presented in terms of the Landauer formalism.

Keywords: quantized conductance, magnetic nanowires, ballistic electron transport, quantum point contacts

Full paper (550kB): M&MS_2006_183.pdf

KRZYSZTOF LANGE

Poznan University of Technology
Institute of Electronics and Telecommunications, Poland
e-mail: lange@et.put.poznan.pl

THERMAL PROPERTIES OF RUBIDIUM FREQUENCY STANDARD

The principle of rubidium standard operation is presented in the paper, with special attention to the influence of temperature on the components of the standard. Next, measurement results of the frequency of the output signal at different, variable temperatures in the environment of the standard itself are presented.

Keywords: Rubidium standards, Hold-Over, synchronization

Full paper (396kB): M&MS_2006_195.pdf

E. STACHOWSKA, G. SZAWIOŁA, A. BUCZEK, W. KOCZOROWSKI, B. FURMANN, D. STEFAŃSKA, A. WALASZYK, J. DEMBCZYŃSKI

Poznań University of Technology
Chair of Quantum Engineering and Metrology, Poland
e-mail: Gustaw.Szawiola@put.poznan.pl

THE APPLICATION OF LASER-MICROWAVE RESONANCE IN TRAPPED RARE-EARTH IONS TO MAGNETOMETRY

The paper describes an application in magnetometry of an experimental set-up for measurement of hyperfine splittings, constructed in the Chair of Quantum Engineering and Metrology, Poznań University of Technology. A method of determination of magnetic flux density on the basis of the measurement of Zeeman splittings of the hyperfine sublevels of atomic (or ionic) electronic levels is discussed. The experimental setup based on a hyperboloidal Paul trap is presented. A review of the current progress of the work and the results hitherto obtained is given.

Keywords: Paul trap, optical-microwave double resonance, magnetometer, atomic clock, frequency standard

Full paper (303kB): M&MS_2006_207.pdf