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1
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Properties of Normal and Superconducting States of Differently Doped REBa_{2}Cu_{3}O_{7-x}

100%
Sułkowski C.
Acta Physica Polonica A
|
1995
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vol. 88
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issue 2
375-380
EN
Temperature dependence of resitivity, ρ(T), thermopower, S_{300}, superconducting transition temperature, T_{c}, and lower critical field, Η_{c1}(0), of differently doped REBa_{2}Cu_{3}O_{7-x} ceramics have been measured. The hole doping of the CuO_{2} plane is determined by the T_{c}, the oxygen concentration and/or the value of the thermopower. The temperature dependence of the resistivity above 200 K and the values of the lower critical field H_{c1}(0) show clear dependence on the hole concentration. Below 200 K, in contrast to simple metals, the resitivity of all samples decreases faster than linearly with the decreasing temperature. Classical electron-phonon scattering mechanism is not appropriate to describe the ρ(T) curves of REBa_{2}Cu_{3}O_{7-x} compounds. Some observed features of the ρ(T) dependence are predicted by mean field phase diagram for the CuO_{2} plane.
2
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Compression Changes in Electrical Resistance and Critical Temperature of Nb_{1-x}Se_2Sn_x Single Crystals

100%
Obolenskiy M., Zavgorodniy A., Vovk R., Nazyrov Z., Goulatis I., Januszczyk M., Latosińska J.
Acta Physica Polonica A
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2012
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vol. 122
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issue 1
159-161
EN
In this work we investigate the influence of hydrostatic pressure (up to 12 kbar) on the critical parameters of Nb_{1-x}Se_2Sn_x (x=0.1 and x=0.15) single crystals. It is shown that a change in the density of states at the Fermi level brings the main contribution to the increase in T_{c} under pressure. Under the effect of hydrostatic pressure, the phonon spectrum is shifted to higher frequencies (narrowed). The estimated Debye temperature is consistent with those obtained from the heat capacity measurements in NbSe_2 single crystals. It is shown that upon increasing hydrostatic pressure the mean free path increases and Nb_{1-x}Se_2Sn_x should be considered as the pure limit in the Ginzburg-Landau theory.
3
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Magnetoresistance and Intrinsic Pinning of Vortices in the Untwinned YBa_2Cu_3O_{7 - δ} Single Crystals with Optimal Oxygen Content and a Small Deviation from the Oxygen Stoichiometry

100%
Vovk R., Gvozdikov V., Obolenskii M., Nazyrov Z., Kruglyak V.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1191-1194
EN
We study the temperature dependence of the in-plane magnetoresistance ρ_{ab}(T) in untwinned YBa_2Cu_3O_{7 - δ} single crystals with the optimal oxygen content and with a small deficit of oxygen atoms at different angles between the external magnetic field 15 kOe and the ab-planes α. We found that at high temperatures in the pseudogap region external magnetic field does not affect the ρ_{ab}(T) but it broadens transitional region T_{c} - T_{c0} from 0.3 K at zero field and α = 0 to approximately 6 K at α = 60° in the field. In case of optimal doping the function ρ_{ab}(T) display a 3D to 2D dimensional crossover when temperature decreases from T_{c} to T_{c0} and scaling near the T_{c0} which we relate to the flux-flow and vortex-lattice melting. In the underdoped sample the vortices are effectively pinned by the random oxygen vacancies and the function ρ_{ab}(T) in transitional region has smooth tails without any traces of crossover and scaling.
4
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Phase-Slip Processes in Superconducting Films: AC Josephson Effect and New Phase Transition

80%
Dmitriev V., Zolochevskii I., Bezuglyi E., Kondrashev D.
Acta Physica Polonica A
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2008
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vol. 114
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issue 1
257-261
EN
The resistive direct current state in wide thin superconducting films as the phase transition from superconducting to normal state is investigated in the absence of external magnetic field. We showed that the states of a wide film with increasing transport current appear in the following order: the superconducting state; the resistive vortex state; the critical state; the new vortex-free resistive state with phase-slip lines; the normal state. We detected the Shapiro current steps on the current-voltage characteristic of the wide film, which arise due to interaction of intrinsic Josephson radiation of phase-slip lines with external microwave irradiation.
5
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Influence of the Granularity on the Transversal Resistance in Y_{0.55}Pr_{0.45}Ba_2Cu_3O_{7-δ} Superconductor

80%
da Luz M., dos Santos C., Machado A.
Acta Physica Polonica A
|
2013
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vol. 124
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issue 4
702-705
EN
This work reports longitudinal (R_{XX}) and transverse (R_{XY}) resistance as a function of temperature measured at low magnetic fields for Y_{0.55}Pr_{0.45}Ba_2Cu_3O_{7-δ} polycrystalline sample. It is observed non-zero transverse resistance at zero applied magnetic field below superconducting transition. The comparison between R_{XX} (T) and R_{XY} (T) curves demonstrate unambiguously that the transverse resistance is related to the double resistive superconducting transition in granular superconductors. I-V curves indicate that the transport properties of the investigated sample are in agreement with the predictions of the two-fluid model.
6
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Influence of Ferromagnetic Layer on Critical Current of a Superconducting Wire

80%
Gömöry F., Vojenčiak M., Šouc J., Seiler E.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
605-608
EN
We investigated how a 10-50 μm layer from soft ferromagnetic material, incorporated in the architecture of a composite superconducting tape, could influence the capability of the tape to transport electrical current. Numerical procedure was developed to calculate the local distribution of magnetic field and current in the condition when all the superconductor is carrying its critical current density. It was found that the concentration of magnetic flux in ferromagnetic layers allows to reduce the local value of magnetic flux density felt by the superconductor. In this way, the critical current of the tape in low applied magnetic fields can be improved. This theoretical prediction is confirmed by experimental observation.
7
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Defect Sensitivity of Magnetic Dot Arrays Influenced by Thermal Activation and Intradot Anisotropy

80%
Baláž P., Horváth D., Gmitra M.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
583-586
EN
The influence of non-magnetic central node defect on magnetic hysteresis of regular square-shaped segment of magnetic dot array with perpendicular uniaxial anisotropy under the thermal activation was investigated via computer simulations based on stochastic Landau-Lifshitz-Gilbert equation. The aim of this study is to point out the simultaneous effect of anisotropy and thermal activation to the dynamical properties of magnetic dot arrays.
8
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Study of Excimer Laser Irradiation Effects on Properties of Crystalline YBaCuO Thin Films

80%
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.
9
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Van Hove Singularity and Superconductivity in Disordered Sr_{2}RuO_{4}

80%
Litak G., Annett J., Györffy B.
Acta Physica Polonica A
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2000
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vol. 97
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issue 1
249-252
EN
On the basis of a simple model we analyse the influence of disorder on critical temperature T_{c} in p-wave superconductors. The disorder is treated by means of the coherent potential approximation and we focus our attention on the effect of a van Hove singularity near Fermi energy E_{F}. For the appropriate values of its parameters our model reproduces the experimentally found behaviour of Sr_{2} RuO_{4}.
10
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DC Characterization of the Coaxial Superconducting Cable

80%
Šouc J., Gömöry F., Vojenčiak M., Frolek L., Isfort D., Ehrenberg J., Bock J.
Acta Physica Polonica A
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2008
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vol. 113
|
issue 1
375-378
EN
Coaxial cable model with superconducting core and superconducting shield conductor was constructed and tested in DC regime. While the core was already examined in our previous works, in this contribution the detailed study of the superconducting shield conductor in DC conditions is presented. It consists of 16 ReBCO coated tapes with critical current 35 A each connected in parallel. Using shunts with known values placed in series the currents in individual tapes were possible to measure. Distribution of the total cable current into the individual tapes was monitored and its influence on critical current of the cable is discussed.
11
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Influence of DC Magnetic Field on AC Loss of YBCO Coated Conductor with Ferromagnetic Substrate

80%
Vojenčiak M., Šouc J., Gömöry F., Seiler E.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
359-362
EN
Most of YBCO tape conductors are prepared on a ferromagnetic substrate. The ferromagnetic material is then exposed to the self magnetic field of the superconductor and also to external magnetic field. In AC magnetic field hysteretic and eddy current losses are generated in the substrate. In this work the AC transport loss of an YBCO coated conductor on a ferromagnetic substrate was measured using electromagnetic method. There are two contributions to total loss - a loss in the superconductor and a loss in the substrate. To suppress the hysteretic loss in the substrate, it is possible to saturate it using DC magnetic field. In this regime significant decrease in total loss was observed.
12
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Dynamics of Hotspot Formation in Nanostructured Superconducting Stripes Excited with Single Photons

80%
Jukna A., Kitaygorsky J., Pan D., Cross A., Perlman A., Komissarov I., Sobolewski R., Okunev O., Smirnov K., Korneev A., Chulkova G., Milostnaya I., Voronov B., Gol'tsman G.
Acta Physica Polonica A
|
2008
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vol. 113
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issue 3
955-958
EN
Dynamics of a resistive hotspot formation by near-infrared-wavelength single photons in nanowire-type superconducting NbN stripes was investigated. Numerical simulations of ultrafast thermalization of photon-excited nonequilibrium quasiparticles, their multiplication and out-diffusion from a site of the photon absorption demonstrate that 1.55 μm wavelength photons create in an ultrathin, two-dimensional superconducting film a resistive hotspot with the diameter which depends on the photon energy, and the nanowire temperature and biasing conditions. Our hotspot model indicates that under the subcritical current bias of the 2D stripe, the electric field penetrates the superconductor at the hotspot boundary, leading to suppression of the stripe superconducting properties and accelerated development of a voltage transient across the stripe.
13
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Content available

Negative Magnetoresistance in the Variable-Range-Hopping Transport of Strongly Underdoped La_{2-x}Sr_xCuO_4

80%
Malinowski A., Cieplak M., Berkowski M., Guha S.
Acta Physica Polonica A
|
2006
|
vol. 109
|
issue 4-5
611-615
EN
The in-plane transport of strongly underdoped La_{2-x}Sr_xCuO_4 films was examined in the magnetic fields up to 14 T and in temperatures down to 1.6 K. While at high temperatures the samples display metallic-like resistivity, the low-T transport is governed by variable-range-hopping mechanism. Careful analysis shows that the temperature dependence of pre-exponential factor in Mott's variable-range-hopping law may not be neglected and that the density of states at the Fermi level can be effectively expressed as g(E-E_F)=N_0 (E-E_F)^p, with a small exponent p of the order of 0.1. In the magnetic field parallel to CuO_2 planes one of the variable-range-hopping parameter,ρ_0, increases by about 20-25%, while the other one, T_0, decreases by about 10-15%, resulting in the decrease in total resistivity. This effect may be related to the decrease of the tunneling barrier between different antiferromagnetic clusters in the presence of magnetic field.
14
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Content available

Asymmetric Tunneling Conductance in Doped Antiferromagnets

80%
Maciąg A., Wróbel P.
|
EN
We calculate the tunneling conductance in the framework of the spin polaron model, which is an effective model for the t-J model, in the limit where at least short-range antiferromagnetic correlations exist. We show that both in the normal state and in the superconducting state the asymmetry of tunneling conductance is present. This fact is the implication of the particle-hole asymmetry of the spin polaron Hamiltonian in the limit of low density of spin polarons which are quasiparticles emerging in a hole doped antiferromagnet. Experimental evidence of analogous asymmetric tunneling conductance was found in the tunneling spectroscopy measurements of high T_c superconductors.
15
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Metal-Insulator Transition in Zinc-Doped LaSrCuO

80%
Malinowski A., Cieplak M., Berkowski M., Plesiewicz W., Skośkiewicz T.
Acta Physica Polonica A
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2006
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vol. 109
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issue 4-5
617-621
EN
The magnetotransport in the vicinity of the metal-insulator transition in La_{1.85}Sr_{0.15}Cu_xZn_{1-x}O_4 is studied in the mK temperature range. Both longitudinal and transverse magnetoresistance are negative indicating the importance of spin effects. The magnitude of transverse magnetoresistance is larger than the magnitude of longitudinal magnetoresistance, indicating the absence of positive orbital magnetoresistance, in sharp contrast to strongly underdoped La_{2-x}Sr_xCuO_4. Both transverse and longitudinal magnetoresistance are proportional to the relative change of zero-field conductivity. This suggests that low-temperature localization of carriers may originate in the spin-disorder scattering on the spin droplets around Zn-impurities.
16
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Thermoelectric Power of MgB_2 Single Crystals Doped with Holes and Electrons

80%
Oganisian K., Rogacki K., Sulkowski C., Zhigadlo N., Katrych S., Karpinski J.
Acta Physica Polonica A
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2008
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vol. 114
|
issue 1
191-195
EN
The thermoelectric power of MgB_2 single crystals, non-substituted, single-substituted with C, and co-substituted with C and Li, was investigated in the temperature range from 10 to 300 K. Both the in-plane (S_ab) and the out-of-plane (S_c) thermoelectric powers are positive for non-substituted crystals and both S_ab and S_c change a sign for crystals doped with electrons when C is substituted for B in the amount larger than 6 at.%. The substitution of C, which supplies electrons mainly into the σ band, reduces the thermoelectric power anisotropy, most likely by increasing the interband scattering. When Li is additionally co-substituted for Mg, S_ab remains unchanged but S_c increases substantially. The Li substitution donates holes into the π band rather than into the σ band and in this way modifies the π band properties, including the possible increase in the intraband scattering.
17
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Effects of Europium-Barium Nonstoichiometry in EBCO123 Systems on Transition and Magnetization Properties

80%
Cigáň A., Maňka J., Kopčok M., Polovková J., Jurdák P., Koňakovský A.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
219-222
EN
We studied the effects of Eu-Ba nonstoichiometry in two series of Eu_{1+x}Ba_{2-x}Cu_3O_{7-δ} and Eu_{1-x}Ba_{2+x}Cu_3O_{7-δ} samples on transition, structural, and magnetic properties. The samples with the nominal composition of 0≤x≤0.07 were synthesized by the solid-state reaction method from Eu_2O_3, BaCO_3, and CuO precursors and sintered at 1050°C for 72 h in flowing oxygen. All the samples show the values of critical temperature T_c, volume density ρ, and maximum volume magnetization M_{max} higher than 90 K, 6.3 g cm^{-3} and 10^4 Am^{-1}, respectively, except for x = 0.07 samples. The Eu-Ba nonstoichiometry in the two series shows different effects on transport, magnetization hystereses, and intergrain properties of the samples.
18
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Strain Relaxation in Thin Films of La_{1.85}Sr_{0.15}CuO_4 Grown by Pulsed Laser Deposition

70%
Zaytseva I., Cieplak M., Abal'oshev A., Berkowski M., Domukhovski V., Paszkowicz W., Shalimov A.
Acta Physica Polonica A
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2007
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vol. 111
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issue 1
185-188
EN
X-ray diffraction, resistivity, and susceptibility measurements are used to examine the effects of film thickness d (from 17 to 250 nm) on the structural and superconducting properties of La_{1.85}Sr_{0.15}CuO_4 films grown by pulsed laser deposition on SrLaAlO_4 substrates. For each d the film sgrow with a variable strain, ranging from a large compressive strain in the thinnest films to a negligible or tensile strain in thick films. Our results indicate that the tensile strain is not caused by the off-stoichiometric layer at the substrate-film interface. Instead, it may be caused by the extreme oxygen deficiency in some of the films.
19
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Universal Relations in the Attractive Hubbard Model with Next-Nearest Neighbor Hopping

70%
Bak M.
Acta Physica Polonica A
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2006
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vol. 109
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issue 4-5
565-568
EN
Recently a new universal relation between superfluid densityρ_s andσ_{dc}T_c, where σ_{dc} is direct current conductivity and T_c - superconducting critical temperature, was found by Homes et al. (Nature 430, 539 (2004)). The theoretical derivation of the relation based on BCS theory is correct only qualitatively. In the present paper this relation is calculated theoretically, using Hartree-Fock approximation and second-order perturbation theory. It is found that although correct qualitatively, quantitatively the results are too small. Inclusion of the second neighbor hopping improves the results.
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