E. I. Buchstab

Interfacial superconductivity in bilayer and multilayer IV–VI semiconductor heterostructures

A comprehensive investigation and comparison of the superconducting properties of bilayer and multilayer epitaxial heterostructures of IV–VI semiconductors exhibiting superconductivity at critical temperatures Tc⩽6.5K is carried out. The superconductivity of these systems is due to inversion of the bands in the narrow-gap semiconductors on account of the nonuniform stresses created by the grids of misfit dislocations arising at the interfaces during the epitaxial growth. It is found that Tc and the character of the superconducting transition of bilayer PbTe∕PbS heterostructures depend on the thickness d of the semiconductor layers and are directly related to the quality of the grids of misfit dislocations at the interfaces (the number and type of structural defects in the grids). Substantial differences in the behavior of bilayer sandwiches and superlattices are found. The minimum thickness d at which superconductivity appears is several times larger for bilayer than for multilayer systems. The upper crit...

Commensurate vortex lattices in thin vanadium films and in V/Si superconducting superlattices

The features of the Shubnikov phase in thin films of type-II superconductors are investigated in the case when the magnetic field is parallel to the surface of the film. Measurements of the nonmonotonic dependence of the critical current Ic on the magnetic field H∥ reveal commensurate vortex lattices with different numbers of vortex chains in the film. It is proved experimentally that in homogeneous films the commensurability effect between the vortex lattice parameter and the thickness of the film can be observed only for the ideal state of the film boundaries, admitting the formation of an infinite lattice of the vortices and their images. Worsening of the film surface smoothness and of the plane-parallel precision of the two surfaces of the film leads to vanishing of the oscillations of Ic and to a sharp decrease of the critical current. The lock-in transition due to the influence of the surface barrier is observed in the films for the first time. It is found that a thin-film layered sample exhibits an...

Superconducting and normal properties of the set of Mo/Si superlattices with variable Si layer thickness

We report the results of the superconducting and kinetic parameter measurements (transition temperature Tc, parallel and perpendicular critical fields Hc2, resistivity in the normal state) on a set of Mo/Si superconducting superlattices with a constant metal layer thickness dMo=22 A and variable semiconducting one dSi(14–44 A). Our data show a monotonic dependence of all measured parameters on dSi. It is found that the Josephson interlayer coupling energy depends exponentially on the spacer thickness. The data obtained allowed us to determine the characteristic electron tunneling length for amorphous silicon with high precision. It is equal to 3.9 A. Enhancement of interlayer coupling leads to the Mo. Si multilayer transition temperature increasing, in agreement with Horovitz theory and with the experimental data on high-Tc materials.

“Quantum - size effect” in Mo/Si multilayers

Abstract The oscillating dependences of some kinetic and superconducting characteristics (ρn, ρ300/ρn, Tc,dHc⊥/dT|Tc) on the multilayer period D have been observed on superlattices Mo/Si. Extremum positions for all these dependences coincide, the period of oscillations being 35 A. These oscillating dependences resemble closely those observed on single films when the quantum size effect takes place. However the explanation of the results for multilayers in the same terms is rather doubtful due to a strong disorder in Mo layers. Different physical characteristics of the multilayers investigated reveal 2D and 3D behavior on the same samples.

Mo/Si superlattices: phase transitions between the commensurate states in the vortex ensemble

The avalanche-type jumps of the resistivity in the mixed state have been observed on the artificial superconducting multilayers Mo/Si with weak Josephson interlayer coupling when an applied magnetic field was oriented along the layer planes. These jumps are periodic with an inverse magnetic field. The simple model is proposed which explains the jump patterns on different samples as the manifestation of the phase transitions between various commensurate states of the vortex lattice. The values of the jump fields and the distances between these fields are quantitatively consistent with the model considered. It is assumed that the set of the jumps corresponds to the sequence of the upper critical fields for different commensurate lattices in the strongly layered superconductor. These phase transitions belong to the class of the first order transitions in distinction to the corresponding transition in homogeneous type-II superconductors. The resistive curves are hysteretic and reveal considerable supercooling.

Commensurate vortex lattices and oscillation effects in superconducting Mo/Si and W/Si multilayers

We report experimental results of a vortex lattice structure investigation in artificial superconducting Mo/Si and W/Si superlattices. Resistance R and critical current Ic measurements in parallel magnetic fields are performed as well as measurements in tilted magnetic fields. At temperatures where the condition of strong layering is satisfied the dependences Ic(H∥) and R(H∥) exhibit oscillatory behavior. It is shown that the appearance of oscillations and of reentrant behavior (vanishing of the resistivity in definite ranges of H∥) are due to the strong intrinsic pinning and to the effect of commensurability between the vortex lattice period and multilayer wavelength. The locations of Ic(H∥) and R(H∥) extrema correspond to the stable states of a commensurate vortex lattice. Our experimental data are in good quantitative agreement with the Ivlev, Kopnin, and Pokrovsky (IKP) theory. It is shown that the values of the commensurability fields depend exclusively on the superlattice period s and anisotropy coe...

2004Transistor in a test tube - harnessing molecular biology to the self-assembly of molecular scale electronics

DNA molecules and homologous genetic recombination processes are harnessed to assemble molecular scale electronics. The highlight is a fully functional field effect transistor assembled in a test-tube, together with the gold wires contacting it. The functional element is a semiconducting single wall carbon nanotube.

Interlayer interaction in Mo/Si superlattices in a normal and superconducting states

Abstract The electronic interlayer interaction in superconducting Mo/Si multilayers was determined by measurements of the upper critical magnetic fields in the superconducting state, and of the magnetoconductivity in the normal state in magnetic fields parallel and perpendicular to the layer planes. These measurements allow the determination of the anisotropy parameter, γ , and of the effective thickness, L eff , which characterize the interlayer interaction between the Mo layers across the Si layer. For Mo/Si series with a constant Si layer thickness, the L eff oscillates as a function of the Mo layer thickness in correlation with the oscillations of the anisotropy parameter γ . The Josephson nature of the interlayer coupling in the superconducting state is confirmed by measurements of the magnetoconductivity on a sample set with a constant Mo layer thickness and variable Si layer thickness. The procedure of evaluating the effective metal layer thickness L eff of the multilayers proposed in this work serves as a new quantitative method to determine the interlayer interaction in the layered systems.

Anisotropy and interlayer interaction in Mo/Si multilayers

Abstract The interlayer interaction in superconducting Mo/Si multilayers is determined by the measurements of the upper critical magnetic field and the magnetoconductivity in magnetic fields, parallel and perpendicular to the layers. From these measurements we determined the anisotropy parameter, γ , and the effective thickness, L eff , which characterize the mutual electronic interaction between the Mo layers across the Si layer. Both quantities oscillate in dependence of the Mo layer thickness for Mo/Si series with constant Si layer thickness.

Interlayer interaction in Mo/Si multilayers

Abstract Interlayer interaction in Mo/Si superconducting multilayers was determined by two methods involving the measurements of the critical magnetic fields and magnetoresistivity (MR) in a normal state at both parallel and perpendicular H orientations. Data on MR allow one to determine the effective thickness of the metal layer L ∗ which characterizes interlayer interaction. On the Mo/Si series with the constant Si layer thickness LSi the oscillations of L ∗ are observed which correlate closely with ones of anisotropy parameter γ. The tunnel (Josephson) nature of the interlayer coupling is confirmed by the data obtained on multilayer series with variable LSi. On these samples the correlation between γ and L ∗ behavior is also found.