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1

Stationary Properties of Superconducting Interferometers

100%

Lewandowski S.

Acta Physica Polonica A

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1991

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vol. 80

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issue 6

841-856

EN

A generalized superconducting interferometer, comprising a parallel arrangement of (lumped) inductances and series (lumped) Josephson junctions is considered. Such a system can be seen as the building block of a simplified model of a high-T_{c} superconductor with its haphazard distribution of Josephson weak links on grain boundaries and lattice defects. It is shown that the system properties can be self-consistently derived from a properly defined potential energy function, taking account of the energies of the system, its current source and external magnetic field. In particular, by solving a stationary problem for this function relative to conditions of constant current bias and constant magnetic flux applied to the system, the critical current of the interferometer can be determined in function of the applied flux. Stationary phase relations and their impact on other system variables are discussed in detail. The theory is applied to the simplest possible system exhibiting all discussed properties, i.e. an interferometer composed of two junctions in series and one junction in parallel.

2

Dynamics of the Josephson Multi-Junction Systems with Junctions Characterized by Non-Sinusoidal Current - Phase Relationship

64%

Abal'osheva I., Lewandowski S.

Acta Physica Polonica A

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2004

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vol. 106

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issue 5

687-691

EN

It is shown that the inclusion of junctions characterized by non-sinusoidal current - phase relationship in the systems composed of multiple Josephson junctions - results in the appearance of additional system phase states. Numerical simulations and stability considerations confirm that these phase states can be realized in practice. Moreover, spontaneous formation of the grain boundary junctions in high-T_c superconductors with non-trivial current-phase relations due to the d-wave symmetry of the order parameter is probable. Switching between the phase states of multiple grain boundary junction systems can lead to additional 1/f noise in high-T_c superconductors.

3

Negative Magnetoresistance of Layered High-t_{c} Compounds

51%

Medvedev Y., Yampolskii S., Lewandowski S.

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vol. 96

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issue 3-4

501-504

EN

Magnetoresistance of layered high-T_{c} systems with quasi-two-dimensional superconductivity in magnetic field H applied parallel to superconducting planes was investigated theoretically. In such configuration an increase in the magnetic field intensity decreases the critical temperature of superconducting regions. It causes both a suppression of the gap parameter Δ and an increase in the tunneling current between the decoupled superconducting planes and, as a consequence, leads to negative magnetoresistance. The dependence of tunneling current on H was calculated for superconducting layer thickness d_{S} smaller than the superconducting correlation length. The results can be used for analysis of current-voltage characteristics of both superconductor-insulator-superconductor and superconductor-insulator normal metal multilayered tunnel structures.

4

X-ray Characterization of Films Formed by Pulsed Laser Deposition on Cold Substrates from YBaCuO Targets

39%

Pełka J., Paszkowicz W., Gierłowski P., Lewandowski S., Zieliński M., Barbanera S., Knapp M.

Acta Physica Polonica A

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2002

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vol. 101

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issue 5

787-794

EN

Grazing-incidence X-ray diffraction supplemented with atomic force microscopy and secondary ion mass spectroscopy were applied to the characterization of films deposited by laser ablation on cold substrates from YBaCuO targets and subsequently irradiated with additional laser pulses of lower energy density. Evolution of X-ray diffraction pattern was observed as a function of irradiation dose. For the as-deposited films the pattern was typical of the amorphized solids. For the films irradiated with doses higher than the threshold, the pattern was enriched with the diffraction peaks, whose general features, like peak positions, widths and relative intensities were almost independent of the dose. The size of the crystallites was deduced from the peak widths to be not smaller than 12-16 nm. Comparison of the pattern with patterns of known phases indicates that, apart of the amorphous component, a structure with an admixture of some new metastable or high temperature phase(s) is formed during the process of pulsed laser annealing. The atomic force microscopy observations revealed that the surface roughness shows a pronounced minimum at low irradiation doses. The secondary ion mass spectroscopy investigation confirms that the strongest chemical changes (increase in concentration of yttrium and copper) due to irradiation with higher doses are observed in the near-surface film material.

5

Study of Excimer Laser Irradiation Effects on Properties of Crystalline YBaCuO Thin Films

39%

Abal'oshev A., Abal'osheva I., Lewandowski S., van der Beek C., Konczykowski M., Rizza G., Barbanera S.

Acta Physica Polonica A

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2004

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vol. 106

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issue 5

681-685

EN

The influence of UV laser irradiation on the physical properties of epitaxial YBa_2Cu_3O_{7-δ} thin (<1μm) films fabricated by laser ablation was studied. The samples were irradiated by pulsed excimer laser beam at different incident energy densities E_{ir}≤130 mJ/cm^2, i.e. 2-3 times below the ablation threshold of YBaCuO. The analysis of the sample cross-section using transmission electron microscope shows that such irradiation forms a disordered layer on the top of the crystalline film. Sample surface amorphization was observed also by atomic force microscope. Due to strong UV irradiation absorption in YBaCuO this surface layer acts like a protective cover for the sample interior. Only a small reduction of superconducting critical temperature T_c was observed. Both transport measurements in normal state and magneto-optical studies in superconducting state indicate that between the disordered layer and the bottom non-modified part of the film there exists a wide transitional region with reduced carrier concentration.

6

Tunneling Conductivity of Manganites with Negative Magnetoresistance

39%

Medvedev Y., Tarenkov V., Svistunov V., Abaloshev A., Abalosheva I., Lewandowski S.

Acta Physica Polonica A

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2000

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vol. 97

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issue 5

827-830

EN

Tunneling investigations of ferromagnetic La_{0.6}Sr_{0.4}MnO_{3} ceramic samples showing negative magnetoresistance effect were carried out in two types of junctions: symmetric "break junctions" and asymmetric ceramics-insulator-metal junctions. The results are consistent with the presence of small ferromagnetic clusters in the insulating barriers of both types of junctions and suggest a two-phase state realized by impurity mechanism of phase separation.

7

Electrical Transport and Magnetic Properties of La_{2/3}Pb_{1/3}MnO_3 Thin Films

33%

Baran M., Berkowski M., Fink-Finowicki J., Lewandowski S., Szymczak H., Szymczak R., Khartchev S., Medvedev Y.

Acta Physica Polonica A

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2004

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vol. 105

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issue 1-2

115-120

EN

The magnetic and transport properties of epitaxial La_{2/3}Pb_{1/3}CuO_3 thin films deposited on SrLaGaO_4 substrate using dc magnetron sputtering technique are reported. The giant magnetoresistance effect (of about 50% at magnetic field of 1 T) was observed near the Curie temperature. Several mechanisms responsible for temperature dependence of resistivity are discussed. The effect of annealing was studied. It shifted the Curie temperature to the lower value, probably, because of the loss of oxygen.

8

Mesoscopic Ordering Effects in Single-Crystalline Thin Films of Lanthanum Manganites

33%

Samoilenko Z., Okunev V., Pushenko E., Abal'oshev A., Baran M., Gierłowski P., Lewandowski S., Szymczak R.

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EN

We have investigated thin films of lanthanum manganites epitaxially grown by pulsed laser deposition on single-crystalline substrates. X-ray diffraction studies show that the characteristic feature of the investigated films is a superposition of fractions with long range atomic order in the basic single-crystalline matrix, and mesoscopic order in the clusterized structure encompassing the Mn-O layers. A detailed analysis of diffusive scattering shows that the size of metallic clusters and their volume concentration in the dielectric matrix varies. In the case of a small size and concentration, the metallic clusters in low temperature behave as quantum dots and their presence leads to a tunneling mechanism of conductivity with characteristic R(T)= const. In the case of large cluster size, the discrete energy levels become smeared. It appears also that the optical, transport, and magnetic properties of the investigated films depend critically on the distribution of Mn^{2+}, Mn^{3+}, and Mn^{4+} ions in the clusters.

9

Atomic Order and the Interaction of Electronic and Magnetic Subsystems in Epitaxial LaSr(Ca)MnO Films

33%

Okunev V., Samoilenko Z., D'yachenko T., Abal'oshev A., Baran M., Gierłowski P., Lewandowski S., Szewczyk A., Szymczak R.

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EN

We have investigated the structure, and electric, optical, and magnetic properties of LaSr(Ca)MnO films containing atomic clusters of various types coherently built into the basic crystallographic matrix. Below the transition to the metallic state, the electrical conductivity of the films is determined by tunneling of charge carriers between metallic clusters. We have found that for each sample there exists a threshold value of magnetic ordering, above which the magnetic subsystem starts to affect actively the film conductivity. The observed increase of conductivity with decreasing temperature is caused by the fact that in the process of magnetic ordering of the samples the cluster size and concentration of metallic phase increase. Experimental results are in agreement with theoretical calculations.

10

Magnetic Properties of FeSeTe Compound Crystallized from Liquid Phase

33%

Lewandowski S., Berkowski M., Tarenkov V., D'yachenko A., Abal'oshev A., Abal'osheva I., Gawryluk D., Domukhovski V., Sidorov S., Boichenko D.

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issue 2

289-291

EN

We report on measurements of samples with nominal composition FeSe_{0.5}Te_{0.5}, crystallized by the Bridgman method. Magnetic and transport properties of the samples were examined. The measurements confirm the coexistence of ferromagnetism and superconductivity below the superconducting transition temperature. The ferromagnetic contribution to magnetization, estimated at 10%, might be caused by the presence of ferrimagnetic Fe_7Se_8, which occupies about 10% of sample volume. From the Andreev spectroscopy we found superconducting energy gap Δ = 2.6 meV at T = 4.2 K, and from magnetization measurements the critical temperature T_c = 15.8 K. The critical current density in magnetic field H = 4 kOe, determined from magnetization measurements, is j_c = (1-2) × 10^4 A/cm^2 and weakly depends on magnetic field intensity.

Refine search results

Stationary Properties of Superconducting Interferometers

Dynamics of the Josephson Multi-Junction Systems with Junctions Characterized by Non-Sinusoidal Current - Phase Relationship

Negative Magnetoresistance of Layered High-t_{c} Compounds

X-ray Characterization of Films Formed by Pulsed Laser Deposition on Cold Substrates from YBaCuO Targets

Study of Excimer Laser Irradiation Effects on Properties of Crystalline YBaCuO Thin Films

Tunneling Conductivity of Manganites with Negative Magnetoresistance

Electrical Transport and Magnetic Properties of La_{2/3}Pb_{1/3}MnO_3 Thin Films

Mesoscopic Ordering Effects in Single-Crystalline Thin Films of Lanthanum Manganites

Atomic Order and the Interaction of Electronic and Magnetic Subsystems in Epitaxial LaSr(Ca)MnO Films

Magnetic Properties of FeSeTe Compound Crystallized from Liquid Phase