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Arxiv.org
by I. K. Yanson; L. F. Rybal'chenko; N. L. Bobrov; V. V. Fisun
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Measurement of the current-voltage characteristics of point contacts makes it possible to study the properties of individual crystallites in a superconducting ceramic. The critical current density in the superconducting regions of the ceramic $\rm La_{1.8}Sr_{0.2}CuO_4$, with a size of the order of several tens of angstroms, is found to attain values of $10^8\ A/cm^2$, which are of the same order of magnitude as the pair-breaking current density, as evaluated from the formulas of the standard...
Topics: Condensed Matter, Superconductivity
Source: http://arxiv.org/abs/1703.08708
Arxiv.org
by I. K. Yanson; N. L. Bobrov; C. V. Tomy; D. McK. Paul
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The electron-quasiparticle interaction (EQI) spectral function has been measured for $\rm DyNi_2B_2C$ in the normal state at low temperatures by means of point-contact spectroscopy (PCS). A low-frequency peak is found around $eV\sim 5\ meV$. It becomes measurable at $T_m^*\simeq 15\ K$ and grows in intensity with constant width as the temperature is lowered. We argue that this peak arises from the strong interaction of conduction electron with coupled crystal-electric-field-phonon excitations...
Topics: Condensed Matter, Superconductivity
Source: http://arxiv.org/abs/1703.04130
Arxiv.org
by I. K. Yanson; N. L. Bobrov; C. V. Tomy; D. McK. Paul
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The superconducting energy gap in $\rm DyNi_2B_2C$ has been investigated using a point-contact technique based on the Andreev reflection from a normal (N)-superconductor (S) boundary, where N is Ag. The observed differential resistance $dV/dI$ is well described by the Blonder-Tinkham-Klapwijk (BTK) theory based on the BSC density of states with zero broadening parameter. Typically, the intensity of the gap structure amounts to several percentage of the normal state resistance, which is an order...
Topics: Condensed Matter, Superconductivity
Source: http://arxiv.org/abs/1702.05785
Arxiv.org
by I. K. Yanson; L. F. Rybal'chenko; V. V. Fisun; N. L. Bobrov; V. V. Demirskii; V. V. Mitkevich
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The point-contact spectra of tetragonal $\rm YBa_2Cu_3O_{7-\delta}$ with $T_c=50-60~K$ are studied at various temperatures. The single-electron energy ($2\Delta_0/kT_c\simeq 17$) and its temperature dependence are determined. The characteristic energies of quasiparticle excitations interacting with conduction electrons in this high-$T_c$. superconductor are found to correlate with the characteristic phonon energies. The possibility of a pair gap, which increases with temperature, is revealed...
Topics: Condensed Matter, Superconductivity
Source: http://arxiv.org/abs/1702.00717
Arxiv.org
by L. F. Rybalchenko; N. L. Bobrov; V. V. Fisun; I. K. Yanson; A. G. M. Jansen; P. Wyder
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The influence of electric felds and currents has been investigated in the high-$T_c$ superconductors $YBaCuO$ and $BiSrCaCuO$ using a point-contact geometry with $Ag$ as the counterelectrode, which reveal switching transitions between states of a different resistance. The origin of this effect in point contacts is associated with electromigration of the oxygen, driven by the electric feld as well as by the currentinduced "electron wind". The switching effect preserves its basic...
Topics: Condensed Matter, Superconductivity
Source: http://arxiv.org/abs/1701.06039
Arxiv.org
by L. F. Rybal'chenko; I. K. Yanson; N. L. Bobrov; V. V. Fisun
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Electron-phonon interaction in superconducting transition metals (Ta, Mo, W) is investigated by the method of point-contact spectroscopy. The spectra obtained are compared with model densities of the phonon states $F(\omega)$ computed from experiments on neutron scattering, and with the tunnel electron-phonon interaction function $g(\omega)$ for Ta. Close agreement between the appropriate spectra is obtained for Ta and Mo, while a significant discrepancy is observed for W, which is the...
Topics: Mesoscale and Nanoscale Physics, Condensed Matter
Source: http://arxiv.org/abs/1702.02916
Arxiv.org
by L. F. Rybal'chenko; V. V. Fisun; N. L. Bobrov; I. K. Yanson; A. V. Bondarenko; M. A. Obolenskii
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A polarity-dependent reversible change in the current-voltage characteristics between states corresponding to different values of the excess current ${{I}_{exc}}$ is observed for bias voltages of several hundred millivolts in $Ag-ReB{{a}_{2}}C{{u}_{3}}{{O}_{7-x}}$ $\left( Re\text{ }=\text{ }Y,\text{ }Ho \right)$ point contacts in the current-carrying state. The observed effect has a high intensity (right up to a complete suppression or recovery of ${{I}_{exc}}$) and is not accompanied by a...
Topics: Condensed Matter, Superconductivity
Source: http://arxiv.org/abs/1703.04132
Arxiv.org
by L. F. Rybal'chenko; V. V. Fisun; N. L. Bobrov; M. B. Kosmyna; A. I. Moshkov; V. P. Seminozhenko; I. K. Yanson
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The maximum value of the energy gap $\Delta\simeq 8\ meV$ and the ratio $2\delta/kT_c\simeq~2.5$ are determined for a high-temperature superconductor $\rm Bi_2Sr_2CaCu_2O_{8+y}$ by using point contacts. It was found that the high-temperature superconductor is transformed under the effect of current injection of quasiparticles to a new modified state with a reduced gap, which is stable in a wide range of injection intensity.
Topics: Condensed Matter, Superconductivity
Source: http://arxiv.org/abs/1701.09124
Arxiv.org
by L. F. Rybal'chenko; I. K. Yanson; V. V. Fisun; N. L. Bobrov; Yu. D. Tret'yakov; A. R. Kaul'; I. E. Graboi
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Electrical characteristics are measured in submicron YBaCuO-normal metal point contacts with a direct conductivity. In a microwave field, such contacts reveal a nonstationary Josephson effect which can occur in the current concentration region not only in the initial weak bonds in YBaCuO but also the weak bonds of a phase-slip center type, formed as a result of a significant current injection (as well as a microwave field). The existence of internal weak bonds in the HTS-electrode contact area...
Topics: Condensed Matter, Superconductivity
Source: http://arxiv.org/abs/1702.01305
Arxiv.org
by I. K. Yanson; L. F. Rybal'chenko; V. V. Fisun; N. L. Bobrov; V. M. Kirzhner; Yu. D. Tret'yakov; A. R. Kaul'; I. E. Graboi
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Point-contacts formed by the high-temperature superconductor $\rm YBa_2Cu_3O_{7-\delta}$ prepared by cryochemical technique, and a noble metal Ag or Cu) are investigated. The maximum value of the energy gap $\Delta\simeq 40~meV$ and the ratio $2\Delta/kT_c\simeq 12$ are obtained. It is found that along certain crystallographic axes of the superconductor under investigation, the electrical resistivity $\lesssim 10^{-5} \Omega\cdot cm$.
Topics: Condensed Matter, Superconductivity
Source: http://arxiv.org/abs/1701.08293
Arxiv.org
by I. K. Yanson; L. F. Rybal'chenko; V. V. Fisun; N. L. Bobrov; M. A. Obolenskii; Yu. D. Tret'yako; A. R. Kaul'; I. E. Graboi
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Electrical characteristics $(I(eV), dV/dI(eV), d^{2}V/dI^{2}(eV))$ are studied comprehensively for pressed submicron point contacts between fresh fractures of LaSrCuO ceramic pellets and a normal metal (Cu). Point contacts (PC) with the direct-type conductivity are investigated, which are characterized by a considerable excess current due to Andreev reflection of quasiparticles at an NS boundary of high transparency. Basic requirements for point contacts suitable for PC measurements are...
Topics: Condensed Matter, Superconductivity
Source: http://arxiv.org/abs/1701.06003
Arxiv.org
by I. K. Yanson; V. V. Fisun; N. L. Bobrov; J. A. Mydosh; J. M. van Ruitenbeek
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The size-effect of Kondo-scattering in nanometer-sized metallic point contacts is measured with the simplified, mechanically-controlled break-junction technique for CuMn alloy of different Mn concentrations: 0.017; 0.035; and 0.18 ($\pm$0.017) at.\%. The results are compared with our previous publication on nominally 0.1 at.\% CuMn alloy \cite{1,2}. The increase of width of the Kondo resonance and enhanced ratio of Kondo-peak intensity to electron-phonon scattering intensity is observed for...
Topics: Mesoscale and Nanoscale Physics, Condensed Matter
Source: http://arxiv.org/abs/1702.03827
Arxiv.org
by L. F. Rybal'chenko; I. K. Yanson; N. L. Bobrov; V. V. Fisun; M. A. Obolenskii; A. V. Bondarenko; Yu. D. Tret'yakov; A. R. Kaul'; I. E. Graboi
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$YBaCuO-Ag$ pressure point contacts with direct conduction are investigated. The excess (relative to the normal state) conductivity mainly caused by fluctuational pairing of electrons above $T_c$ is measured in the temperature interval 100-200~$K$. The superconductivity above 120~$K$ is found to be of the two-dimensional type. The obtained preliminary results indicate the presence of small amount of an unknown phase with $T'_c\gtrsim 200~K$ in $YBaCuO$.
Topics: Condensed Matter, Superconductivity
Source: http://arxiv.org/abs/1701.06035
Arxiv.org
by I. K. Yanson; L. F. Rybal'chenko; V. V. Fisun; N. L. Bobrov; M. A. Obolenskii; N. B. Brandt; V. V. Moshchalkov; Yu. D. Tret'yakov; A. R. Kaul'; I. E. Graboi
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The energy gap has been measured and the characteristic phonon energies determined for the superconducting compound $La_{1.8}Sr_{02}CuO_4$ from the current-voltage characteristics of point contacts with a copper counterelectrode. The temperature dependence of the energy gap was determined. pacs 73.40.Jn, 74.25.Kc, 74.45.+c, 73.40.-c, 74.20.Mn, 74.70.Ad, 74.72.-h, Dn
Topics: Condensed Matter, Superconductivity
Source: http://arxiv.org/abs/1701.01982
Arxiv.org
by B. I. Verkin; B. B. Banduryan; A. S. Barylnik; A. G. Batrak; N. L. Bobrov; I. S. Braude; Yu. L. Gal'chinetskaya; A. L. Gaiduk; A. M. Gurevich; V. V. Demirskii; V. I. Dotsenko; V. I. Eropkin; S. V. Zherlitsyn; A. P. Isakina; I. F. Kislyak; V. A. Konovodchenko; F. F. Lavrent'ev; L. S. Litinskaya; V. A. Mikheev; V. I. Momot; V. D. Natsik; I. N. Nechiporenko; A. S. Panfilov; Yu. A. Pokhil; A. I. Prokhvatilov; E. Ya. Rudavskii; L. F. Rybal'chenko; I. V. Svechkarev; A. M. Stepanenko; M. A....
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The structure and physical properties of superconducting compounds Y(La)-Ba(Sr)-Cu-O are studied, the compounds being prepared by the method of cryogenic dispersion of a charge consisting of premix oxides and carbonates. Electrical conductivity and critical current density of the superconductors are measured over a wide temperature range of 10~$mK$ to 300~$K$. Degradation of the superconductor critical parameters in time and structural characteristics, magnetic susceptibility, heat capacity and...
Topics: Condensed Matter, Superconductivity
Source: http://arxiv.org/abs/1703.08707