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1
Content available remote

Superconductivity in ThIr₂Si₂

100%
Domieracki K., Kaczorowski D.
Acta Physica Polonica A
|
2016
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vol. 130
|
issue 2
593-596
EN
The compound ThIr₂Si₂ crystallizes with a tetragonal crystal structure of the CaBe₂Ge₂-type (space group P4/nmm). Its low-temperature physical properties were investigated by means of magnetization, electrical resistivity, and heat capacity measurements, performed down to 0.35 K. The experiments revealed bulk superconductivity below T_{c} = 2 K. The obtained data indicate that ThIr₂Si₂ is a weakly-coupled type-II BCS superconductor.
2
Content available remote

Magnetic Anisotropy of Fe Films in MgO/Cu(t_{Cu})/Fe/Cu Systems

80%
Baszyński J., Toliński T.
Acta Physica Polonica A
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1997
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vol. 91
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issue 2
245-248
EN
Ferromagnetic resonance was employed to study the magnetic anisotropy of the Fe thin film in the MgO/Cu(t_{Cu})/Fe/Cu system. The Fe film showed strong fourfold cubic anisotropy (H_{K_{1}} = 2K_{1}/M = 46.15 kA/m) for t_{Fe} = 23 nm and t_{Cu} = 0. The spread of the crystallographic axes Δβ = 0.5° was evaluated from the angular dependence of the resonance line width ΔH_{pp} (4.4 < ΔH_{pp} < 6.4 kA/m). Such a small mosaicity confirmed the epitaxial growth of the Fe film. The Cu buffer layer destroys this growth of the Fe film which showed only a weak anisotropy.
3
Content available remote

Universal Critical Quantum Properties of Cuprate Superconductors

80%
Schneider T.
Acta Physica Polonica A
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1997
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vol. 91
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issue 1
203-212
EN
Using the scaling theory of quantum critical phenomena we explore the occurrence of universal critical behavior at the insulator-to-superconductor and superconductor-to-normal state transitions at zero temperature. Experimentally, these phase transitions are driven by doping and correspond to critical end points of the phase transition line in the temperature-hole concentration plane. Provided that the order parameter is a complex scalar in two dimensions, and that the London relation between superfluid number density and magnetic penetration depth holds, the scaling theory predicts universal behavior close to the insulator-to-superconductor transition. In particular, transition temperature and zero temperature penetration depth are universally related and the sheet resistance adopts a universal value. These predictions agree remarkably well with available experimental data and provide useful constraints for a microscopic theory.
4
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Non-Fermi Liquid States of a General Model of Copper-Oxide Metals

80%
Varma C. M.
Acta Physica Polonica A
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1997
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vol. 91
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issue 1
191-201
EN
A summary is given of the minimum requirements posed by experimental results on a theory of copper-oxide metals and of the recent solution of a model of copper-oxygen bonding and anti-bonding bands with the most general two-body interactions allowable by symmetry which satisfies these requirements. Several experiments were proposed to test the theory.
5
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Ultrathin Niobium in the Si/Nb/Si Trilayers

80%
Zaytseva I., Abal'oshev O., Dłużewski P., Minikayev R., Cieplak M., Zhu L., Chien C.
|
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vol. 126
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issue 4a
A-140-A-144
EN
We study magnetotransport properties of the Si/Nb/Si trilayers, in which the thickness of niobium, d, changes from 1.1 nm to 50 nm, while the thickness of Si is fixed at 10 nm. The niobium films are amorphous for d < 4 nm, while in thicker films the alligned polycrystalline grains are formed. We observe that the Hall coefficient changes sign into negative in the films with d < 1.6 nm. We also find that in the ultrathin films the magnetic field induces a transition from the superconducting into a metallic phase with the resistance smaller than the normal-state resistance.
6
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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.
7
Content available remote

Coherence Lengths for Superconductivity in the Two-Orbital Negative-U Hubbard Model

80%
Litak G., Örd T., Rägo K., Vargunin A.
Acta Physica Polonica A
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2012
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vol. 121
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issue 4
747-751
EN
We study the peculiarities of coherency in the superconductivity of two-orbital system. The superconducting phase transition is caused here by the on-site intra-orbital attractions (negative-U Hubbard model) and inter-orbital pair-transfer interaction. The dependencies of critical and non-critical correlation lengths on interaction channels and band fillings are analyzed.
8
Content available remote

On the Current Flow in Superconductors: Universal Trends and Holographic Analysis

80%
Rogatko M., Wysokiński K.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
376-379
EN
The superconducting state can be destroyed by the increase of temperature, magnetic field or current flow beyond their critical values. The critical current I_{c} is of special interest as most of the practical applications of superconductors crucially depend on its limiting value. Recent analysis of experimental data in many families of type I and type II superconductors have discovered an interesting universal relation between critical current density j_{c}, the critical magnetic field H_{c} and the penetration depth λ. For type II superconductors the role of the thermodynamic critical field H_{c} is played by the lower critical field H_{c1} and ratio between the relevant dimension of the system d with respect to the penetration depth matters. Thus the effective dimensionality of the system is important and rules the system behaviour. It turns out that the holographic analogy provides an interesting justification of the above findings. We have calculated the temperature dependence of the critical current in the strongly coupled holographic superconductors with the current flow. It has been found that, independently of the symmetry of the order parameter, the critical current depends on temperature in 2d systems as I_{c} ∝ (T_{c}-T)^{3/2} and agrees with that observed in thin films (d < λ). Similar calculations for 3d systems (d > λ) reveal linear T-dependence I_{c} ∝ (T_{c}-T).
9
Content available remote

Changes in YBCO Single Grain Bulk Superconductor Exposed to Air Moisture

80%
Piovarči S., Antal V., Kaňuchová M., Radušovská M., Diko P.
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vol. 126
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issue 1
364-365
EN
Changes in bulk single grain YBCO superconductor at exposition to air were studied. The increase of the sample weight caused by reaction with air moisture was observed by weighing the samples over two months period. Thermal analyses and mass spectrometry of the exposed samples has shown evolution of water and oxygen during sample heating. Observation with scanning electron microscope confirmed the formation of some nanosize phases at the inner sample surfaces. XPS spectra done on the freshly cleaved and on the air exposed (001) surfaces confirmed changes in Ba and Cu bonds. Observed structural changes did not caused systematic changes in measured trapped field.
10
Content available remote

The Pseudogap Phenomenon in High-T_{c} Superconductors

80%
Ranninger J., Romano A.
Acta Physica Polonica A
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2000
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vol. 97
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issue 1
157-164
EN
We review the possible mechanisms leading up to the phenomenon of a pseudogap which characterizes the normal-state properties of high-T_{c} superconductors. We suggest that this pseudogap is not due to superconducting phase fluctuations and hence is not related to a crossover between a BCS state of Cooper pairs and a Bose-Einstein condensation of local pairs. We rather argue that it is due to uncorrelated pairing which is already manifest in the local electronic structure and accessible by photoemission and tunneling experiments.
11
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Raman Scattering Study of (Sr,Ca)_{10}Cu_{17}O_{29} Single Crystals

80%
Strzeszewski J., Szymczak H., Leonyuk L., Szymczak R.
Acta Physica Polonica A
|
2000
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vol. 98
|
issue 4
429-439
EN
Polarized Raman spectra of high temperature superconducting single crystals of A_{10}Cu_{17}O_{29} (A_{10}=Ca_{4.7}Sr_{4.1}Bi_{0.3}) were studied in various scattering configurations in the range of 40-700cm^{-1}. In very distinctive spectra there were found over 20 peaks. It was observed that the flat continuum of electronic excitations in the normal state was redistributed below the critical temperature. The frequency dependent redistribution is consistent with the value of energy gap estimated using tunnelling spectroscopy techniques.
12
Content available remote

Fano Resonance in a Coupled Electron-Phonon System

80%
Falkovsky L. A., Klama S.
Acta Physica Polonica A
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1997
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vol. 91
|
issue 2
347-350
EN
Raman light scattering with excitation of electron-hole continuum and a phonon is investigated theoretically. The effect of a surface and screening of the electron-photon coupling and of the deformation potential as a result of the Coulomb interaction of the electrons is taken into account. The parameters of the 340 cm^{-1} resonance line in superconducting YBaCuO are estimated by comparing with experimental data.
13
Content available remote

Superconductivity in Lu_xZr_{1-x}B_{12} Dodecaborides with Cage-Glass Crystal Structure

80%
Sluchanko N., Azarevich A., Bogach A., Gavrilkin S., Glushkov V., Demishev S., Mitsen K., Shitsevalova N., Filippov V., Gabani S., Flachbart K.
Acta Physica Polonica A
|
2017
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vol. 131
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issue 4
1036-1038
EN
We probed the evolution of the superconducting transition temperature T_c and the normal state parameters of Lu_xZr_{1-x}B_{12} solid solutions employing resistivity, heat capacity and magnetization measurements. In these studies of high-quality single crystals it was found that there are two types of samples with different magnetic characteristics. An unusually strong suppression of superconductivity in Lu_xZr_{1-x}B_{12} with a rate dT_c/dx=0.21 K/at.% of Lu was observed previously on the first "magnetic" set of crystals, and it was argued to be caused by the emergence of static spin polarization in the vicinity of non-magnetic lutetium ions. On the contrary, the second (current) set of "nonmagnetic" crystals demonstrates a conventional T_c(x) dependence with a rate dT_c/dx=0.12 K/at.% of Lu which is typical for BCS-type superconductors doped by nonmagnetic impurities. The reason for this difference is yet unclear. Moreover, the H-T phase diagram of the superconducting state of Lu_xZr_{1-x}B_{12} (0 ≤ x ≤ 1) solid solutions has been deduced from magnetization measurements.
14
Content available remote

Superconductivity in Anderson Lattice Model

80%
Romano A., Noce C., Micnas R.
Acta Physica Polonica A
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1997
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vol. 91
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issue 2
381-385
EN
We study the superconducting instabilities generated by the inclusion in the Anderson lattice model of a density-density attractive potential between correlated electrons on nearest-neighbouring sites. Using a description of the normal phase based on a perturbative expansion around the atomic limit, we treat the attractive potential in the broken-symmetry Hartree-Fock scheme and analyze which of the possible symmetries of the superconducting order parameter leads to the highest possible transition temperature in the case of a two-dimensional square lattice. For values of the on-site f-repulsion large compared to the hopping amplitude, a suppression of any possible superconducting phase occurs, regardless of the symmetry of the order parameter.
15
Content available remote

Superconducting states of the cylinder with a single vortex in magnetic field according to the Ginzburg-Landau theory

70%
Zharkov G.
Open Physics
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2005
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vol. 3
|
issue 1
77-103
EN
Self-consistent solutions of the nonlinear Ginzburg-Landau (GL) equations are investigated numerically for a superconducting (SC) cylinder, placed in an axial magnetic field, with a single vortex on the axis (m=1). Two modes, which show the original state of the cylinder, SC or normal (s 0 andn 0), are studied. The field increase (FI) and the field decrease (FD) regimes are studied. The critical fields destroying the SC state withm=1 are found in both regimes. It is shown that in a cylinder of radiusR and GL-parameter ϰ, there exist a number of solutions depending only on the radial co-ordinater corresponding to different states such as M,e, d, p,i, n, $$\bar n$$ ,n *, and the state diagram on the plane of the variables (ϰ,R) is described. The critical fields corresponding to intrastate transitions and the onset of hysteresis are obtained. The critical fieldH 0(R) dividing the paramagnetic and diamagnetic states of the cylinder withm=1 is determined. The limiting fields of supercooling or superheating of the normal state at which the restoration of the SC state occurs are established. It is shown, that (in both casesm=1,0) there exist two critical parameters, $$\kappa _0 = {1 \mathord{\left/ {\vphantom {1 {\sqrt 2 = 0.707}}} \right. \kern-\nulldelimiterspace} {\sqrt 2 = 0.707}}$$ and $$\kappa _0 = 0.93$$ , which divide bulk SC into three groups (with $$\kappa< \kappa _0 ,\kappa _0 \leqslant \kappa \leqslant \kappa _c $$ and $$\kappa > \kappa _c $$ ), in accordance with the behavior in a magnetic field. The parameters $$\kappa _0 $$ and $$\kappa _c $$ mark the boundary for the existence of a supercooled normal $$\bar n$$ -state in FD-regime and a superheated SC M-state in FI-regime respectively. It is shown, that the value $$\kappa _* = 0.417$$ , which was claimed in a number of papers as related to type-I superconductors, is illusory.
16
Content available remote

Critical fields of a superconducting cylinder

70%
Zharkov G.
Open Physics
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2004
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vol. 2
|
issue 1
220-240
EN
The self-consistent solutions of the nonlinear Ginzburg-Landau equations, which describe the behavior of a superconducting mesoscopic cylinder in an axial magnetic field H (provided there are no vortices inside the cylinder), are studied. Different, vortex-free states (M-, e-, d-, p-), which exist in a superconducting cylinder, are described. The critical fields (H 1, H 2, H p, H i, H r), at which the first or second order phase transitions between different states of the cylinder occur, are found as functions of the cylinder radius R and the GL-parameter $$\kappa $$ . The boundary $$\kappa _c (R)$$ , which divides the regions of the first and second order (s, n)-transitions in the icreasing field, is found. It is found that at R→∞ the critical value, is $$\kappa _c = 0.93$$ . The hysteresis phenomena, which appear when the cylinder passes from the normal to superconducting state in the decreasing field, are described. The connection between the self-consistent results and the linearized theory is discussed. It is shown that in the limiting case $$\kappa \to {1 \mathord{\left/ {\vphantom {1 {\sqrt 2 }}} \right. \kern-\nulldelimiterspace} {\sqrt 2 }}$$ and R ≫ λ (λ is the London penetration length) the self-consistent solution (which correponds to the socalled metastable p-state) coincides with the analitic solution found from the degenerate Bogomolnyi equations. The reason for the existence of two critical GL-parameters $$\kappa _0 = 0.707$$ and $$\kappa _0 = 0.93$$ in, bulk superconductors is discussed.
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