Searcharxiv⌕ Search

arXiv subjects

I. K. Yanson

Publications and source records attributed to I. K. Yanson.

At least 19 recordsLinked to original sources
arXiv2018

Micro(point)contact spectroscopy of dilute magnetic (Kondo) alloys CuMn and CuFe

The method of microcontact spectroscopy is used to study alloys with magnetic impurities CuMn and CuFe in the range of concentrations 0.01-1 at.%. Minima or maxima (so-called zero-bias anomalies) were observed in the microcontact spectra of these alloys at voltages ~ 1 mV. The Lande g-factor for the Mn impurity in a Cu matrix was determined from the splitting of the minimum of the zero-bias anomaly in a magnetic field. The quantitative calculations carried out agree well with theory and permit determining both the important geometric contact parameter i.e., the averaged geometric form factor, and the characteristics of the alloy itself, for example, J/E_F, i.e., the ratio of the magnitude of the exchange interaction energy between an electron and the magnetic impurity to the Fermi energy, from the microcontact spectra.

cond-mat.mes-hall↗
arXiv2017

Influence of nonequilibrium phonons on the amplitude of magnetoquantum oscillations in the point-contact resistance

For metallic point contacts with Be and Al the magnetoquantum oscillations in the contact resistance have been investigated as a function of the applied voltage over the contact. For one set of point contacts the oscillation amplitude is found to vary nonmonotonously with the applied voltage with similarities to the point-contact spectrum of the electron-phonon interaction. The other part of the investigated point contacts shows a decrease of the oscillation amplitude with increasing bias voltage. For the understanding of the voltage dependence of the amplitude of the point-contact magnetoresistance oscillations the influence of nonequilibrium phonons generated by the ballistically injected electrons will be discussed.

cond-mat.mes-hall↗
arXiv2017

Critical current density in the superconducting ceramic $\rm La_{1.8}Sr_{0.2}CuO_4$ in S-c-N point contacts

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 theory of superconductivity.

cond-mat.supr-con↗
arXiv2017

Structure and physical properties of superconducting compounds Y(La)-Ba(Sr)-Cu-O

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 acoustic properties are studied, and current-voltage characteristics are determined.

cond-mat.supr-con↗
arXiv2017

Reversible recovery of excess current in $Y(Ho)-Ba-Cu-O$-normal metal point contacts under high voltages

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 noticeable variation of the energy gap or the critical temperature in the point contact region. It is also established that the states with intermediate values of $I_{exc}$ are stable for zero bias voltages across the point contacts, at least up to $110 \ K$. It is assumed that the variation of ${{I}_{exc}}$ and the corresponding modification of IVC are due to the oxygen migration processes induced by the electric field and current, resulting in a local variation of the superconducting parameters in the point-contact region.

cond-mat.supr-con↗
arXiv2017

Electron-quasiparticle interaction in $\rm DyNi_2B_2C$ measured by point-contact spectroscopy

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 whose branches cross at low energy. The comparison with PC spectra for $\rm HoNi_2B_2C$ suggests that a similar peak also exists for this compound. The magnitude of the point-contact EQI parameter $λ_{PC}$ for $\rm DyNi_2B_2C$ is estimated. $©$2000 Published by Elsevier Science B.V. All rights reserved.

cond-mat.supr-con↗
arXiv2017

Point-contact spectroscopy of superconducting energy gap in $\rm DyNi_2B_2C$

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 of magnitude less than predicted by the theory. For $\rm DyNi_2B_2C$ with $T_c<T_N$ (the Neel temperature), we found gap values satisfying the ratio of $2Δ_0/k_BT_c=3.63\pm 0.05$ similar to other superconducting nickel-borocarbides, both nonmagnetic and magnetic with $T_c\geq T_N$. The superconducting gap nonlinearity is superimposed on the antiferromagnetic structure in $dV/dI(V)$ which is suppressed at the magnetic field of the order of 3T applied nominally in the $ab$-plane and temperature $\geq 11~K$. The observed superconducting properties depend on the exact composition and structure at the surface of the crystal.

cond-mat.supr-con↗
arXiv2017

Size-effect of Kondo scattering in point contacts (revisited)

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 contacts with sizes smaller than 10 $nm$. From the comparison of electron-phonon scattering intensity for the pressure-type contacts, which correspond to the clean orifice model, we conclude that the size effect is observed in \emph{clean} contacts with the shape of a \emph{channel} (nanowire).

cond-mat.mes-hall↗
arXiv2017

Point-contact spectroscopy of tantalum, molybdenum, and tungsten

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 $F(ω)$ computed from experiments on neutron scattering, and with the tunnel electron-phonon interaction function $g(ω)$ 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 appearance of a blurred maximum instead of the two expected separated peaks on the point-contact spectra. The absolute intensities of a number of point-contact spectra $G(eV)$ and electron-phonon coupling constants $λ$ are calculated. For all three metals the values obtained turned out to be considerably below those expected. The possible reasons for this disagreement are discussed.

cond-mat.mes-hall↗
arXiv2017

"Internal" coherent effects in HTS-normal metal point contacts

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 produces a narrow minimum in the differential resistance near zero biases. Moreover, the effect of magnetic flux quantization is observed for separate granules in magnetic fields stronger than the first critical field.

cond-mat.supr-con↗
arXiv2017

Point-contact spectroscopy of superconducting YBaCuO single crystals of tetragonal modification

The point-contact spectra of tetragonal $\rm YBa_2Cu_3O_{7-δ}$ with $T_c=50-60~K$ are studied at various temperatures. The single-electron energy ($2Δ_0/kT_c\simeq 17$) 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 near the critical temperature.

cond-mat.supr-con↗
arXiv2017

Point-contact spectroscopy of the high-temperature superconductor BiSrCaCuO

The maximum value of the energy gap $Δ\simeq 8\ meV$ and the ratio $2δ/kT_c\simeq~2.5$ 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.

cond-mat.supr-con↗
arXiv2017

Point-contact studies of high-temperature superconductor $\rm YBa_2Cu_3O_{7-δ}$

Point-contacts formed by the high-temperature superconductor $\rm YBa_2Cu_3O_{7-δ}$ prepared by cryochemical technique, and a noble metal Ag or Cu) are investigated. The maximum value of the energy gap $Δ\simeq 40~meV$ and the ratio $2Δ/kT_c\simeq 12$ are obtained. It is found that along certain crystallographic axes of the superconductor under investigation, the electrical resistivity $\lesssim 10^{-5} Ω\cdot cm$.

cond-mat.supr-con↗
arXiv2017

Investigation of energy gap and observation of electron-phonon interaction in high-temperature superconductor $La_{1.8}Sr_{0.2}CuO_{4}$ - normal metal point contacts

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 formulated. The models of investigated point contacts permitting the interpretation of the observed characteristics are considered. The results of measurement of the energy gap reveal that LaSrCuO is a superconductor with a strong coupling since the maximum value of the ratio $2Δ/kT\simeq 11$. It is found that superconducting properties may vary appreciably over distances of several tens of angstroms, resulting in some cases in the simultaneous emergence of two gaps corresponding to two critical temperatures. The $dV/dI(eV)$ and $d^{2}V/dI^{2}(eV)$ curves display some high-intensity singularities whose position on the eV-axis is practically independent of temperature and correlates with the phonon spectrum obtained in neutron scattering experiments. This points to a strong electron-phonon interaction in LaSrCuO.

cond-mat.supr-con↗
arXiv2017

Excess conduction of YBaCuO point contacts between 100 and 200 K

$YBaCuO-Ag$ 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 $YBaCuO$.

cond-mat.supr-con↗
arXiv2017

Reversible transitions in high-$T_c$ cuprates based point contacts

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 features at elevated temperatures up to room temperature and in high magnetic felds up to 10 T.

cond-mat.supr-con↗
arXiv2017

Point-contact measurements of the energy gap of lead-chalcogenide-based superconducting superlattices

The energy gap of superconducting $PbTe-PbS$ semiconductor superlattices has been analyzed with the help of point contacts for the first time below the critical temperature, $T_{c}=3.9~K$, and in the fluctuation region $T>T_{c}$. The size of the gap and its dependence on the temperature and field are determined by the position of the point contact inside the superlattice. \pacs{73.40.Jn, 74.25.Kc, 74.45.+c, 74.50.+r., 73.40.-c, 74.78.-w, 74.78.Fk, 74.20.Mn, 74.40.+k.-n, 74.45.+c, 74.62.Dn, 74.70.Ad

cond-mat.supr-con↗