Critical current of SFIFS tunnel junctions: Spin-orbit scattering effects

The proximity effect of a bulk superconductor (S) and a thin normal ferromagnetic metal layer (F) containing spin-orbit scattering centers is studied. The weak and strong limits of the proximity effect in the SF bilayer are considered analytically in the framework of the microscopic model of the superconducting state of dirty metals. The critical current of an SFIFS tunnel junction (I stands for an insulating layer) whose sides are made of proximity-coupled SF layers is calculated. Effects of spin-orbit scattering in the F layers on tunneling current are studied for parallel and antiparallel magnetization vectors of the F layers. It is shown that there is a complex relation between the magnitude of the superconducting current flowing through the SFIFS junction and scattering: spin-orbit scattering suppresses the exchange field effect in a nonlinear way and, at a fixed concentration of scattering centers, depends on the SF boundary resistance and the strength of the proximity effect.     

Critical current in SFIFS junctions

A quantitative theory of the Josephson effect in SFIFS junctions (S denotes bulk superconductor, F is metallic ferromagnet, and I is insulating barrier) is presented in the dirty limit. A fully self-consistent numerical procedure is employed to solve the Usadel equations for arbitrary values of the F-layer thicknesses, magnetizations, and interface parameters. In the case of antiparallel ferromagnet magnetizations, the effect of critical current I _c enhancement by the exchange energy H is observed, while in the case of parallel magnetizations the junction exhibits a transition to the π state. In the limit of thin F layers, we study these peculiarities of the critical current analytically and explain them qualitatively; the scenario of the 0-πtransition in our case differs from those studied before. The effect of switching between 0 and π states by changing the mutual orientation of F layers is demonstrated.     

Topological quantization of current in quantum tunnel contacts

It is shown that an account of the Berry phase (a topological ϑ-term), together with a dissipative term in the effective action S[ϕ] of the tunnel contacts, induces a strong quantization of the tunnel current at low temperatures. This phenomenon, as the Coulomb blockade, reflects a discrete charge structure of the quantum shot noise and can ensure a quantization of the tunnel current without a capacitive charging energy E _C when the latter is strongly suppressed by quantum fluctuations. Since the value of the ϑ parameter is determined by the gate voltage, this effect allows us to control the current through the contact. A possible physical application of this effect is proposed. The text was submitted by the author in English.     

Reversal of sign of the Hall coefficient in n-InSb in the magnetic freeze out regime

Change in sign of the Hall coefficient has been observed in n-InSb with carrier concentrations ranging from 2 × 10¹⁴ cm^?3 to 6 × 10¹⁴ cm^?3, which occurs at liquid helium temperatures and magnetic fields above 30 kG. The influence of the compensation ratio, temperature, and geometry has been investigated.     

Metal point contacts and metal-oxide tunnel barriers fabricated with an AFM

We report the fabrication of atomic point contacts and lateral tunnel junctions by using anodic oxidation of thin metal films with an atomic force microscope.In situelectrical measurements were used as feedback to control the fabrication of metal nanowires that were subsequently anodized through their cross section to form point contacts and tunnel junctions. When the conductance of an Al device is reduced below 5×10⁻⁴S it starts to decrease in discrete steps of 2e²/h. In some devices we are able to stabilize the conductance at a value near 2e²/hwhich corresponds to a single, atomic-sized conducting channel. Similar experiments on Ti devices result in a continuous decrease of the conductance and the formation of stable tunnel junctions. This continuous behavior is a result of the large series resistance and the small oxide barrier height of the Ti/TiO_xsystem.     

Database of amino acid-nucleotide contacts in contacts in DNA-homeodomain protein

The analysis of amino acid-nucleotide contacts in interfaces of the protein-DNA complexes, intended to find consistencies in the protein-DNA recognition, is a complex problem that requires an analysis of the physicochemical characteristics of these contacts and the positions of the participating amino acids and nucleotides in the chains of the protein and the DNA, respectively, as well as conservatism of these contacts. Thus, those heterogeneous data should be systematized. For this purpose we have developed a database of amino acid-nucleotide contacts ANTPC (Amino acid Nucleotide Type Position Conservation) following the archetypal example of the proteins in the homeodomain family. We show that it can be used to compare and classify the interfaces of the protein-DNA complexes.     

相干输运中的接点问题

为了研究介观体系的相干输运中接点的重要作用,采用一简单的纳米单势垒“二维-一维-二维”(2D-1D-2D)模型,应用散射矩阵方法和托马斯-费米近似,计算了体系透射率和在直流电压下电势分布. 结果表明： 1)接点对其透射率有显著的影响; 2)电势降落表现的电导性质违背了与经典串联电路中等价的基尔霍夫定律. 因此介观体系中各器件与接点间是量子相干的,考虑接点问题有利于对介观体系相干输运更为深入的研究. 关键词： 相干输运 接点 介观体系     

Reversal of the Hall field in indium

The Hall effect in single crystal has been investigated at 63 kOe over the 6–280 K temperature range. The Hall coefficient reverses sign as a function of temperature. The high temperature value is less negative then theoretical predictions.     

Transport critical-current and voltage-current characteristics of Bi(2223) silver-clamped thick films

The transport critical current properties of Bi(2223) silver-clamped thick films are studied by the measurement of its dependence on magnetic field and temperature close to T _c. It is found that the transport critical current follows a power law J _c(1–T/T _c)^3/2 for the sample with J _c>2.0×10⁴ A/cm² (77K, zero field) and that J _c(H) is basically reversible for increasing and decreasing magnetic field. After the transport current exceeds the critical current, the voltage-current (V-I) characteristics show a flux-creep-like behaviour until they smoothly join the flux-flow state. From the measurement of V-I curves, the pinning property of the sample may be estimated using the flux-creep mode. The flux-flow resistance is found to have a nonlinear magnetic field dependence.     

Fronts in distributed Josephson contacts

The dynamics of fluxons (magnetic-flux quanta) in extended Josephson contacts is studied. Graphs of fluxon velocity versus the contact parameters are obtained. The existence of both stable single photons and photon packets is discovered.Nizhegorod State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 34, No. 8, pp. 956–966, August, 191.     

Reversal of the magnetic interaction in hydrogenated Pd-Mn alloys

We have measured the properties of some Pd_1?xMn_x and Pd_1?xMn_xH_y alloys using a low field a.c. technique. For x<4%, we observe a change over from ferromagnetism (when y = 0) to antiferromagnetism (when y ≌ 0.7). The properties of the hydrogenated alloys are compared with the similar $\text{Ag}$Mn alloys.     

Reversal of waves in forward-scattering location

Potentialities of the pulsed acoustic forward-scattering location with the use of time separation of the intense direct and weak scattered signals propagating at a small angle to one another are considered. Two types of interference are taken into account: nonstationary observation conditions under the effect of currents, which affect the arrival times of the direct and scattered signals, and nonstationary reverberation. It is shown that, in the presence of these interferences, the application of the correlation transformation equivalent to the time reversal of waves has an advantage over the conventional location technique based on the determination of the signal travel times.     

Theory of superconducting contacts

Metallic contacts between superconducting and normal films are known to have a pair-breaking effect on the electron pairs. By limiting our considerations to the gapless regime and to contacts between superconducting and paramagnetic metals the features of this pair-breaking mechanism are investigated. We compute the normalization of the order parameter and with it such quantities as the tunneling conductance, electrical and thermal conductivity and the critical current parallel to the contact. Furthermore we investigate the influence of a magnetic field. By calculating the? ₂(t)-parameter we demonstrate the interplay between the different pair-breaking mechanisms in perpendicular and parallel fields. In the latter case we discuss the influence of the contact on the superconducting sheath proposed bySaint-James andde Gennes. Experiments to test the present theory are suggested.