Magnetism in atomic-size palladium contacts and nanowires

We have investigated Pd nanowires theoretically, and found that, unlike either metallic or free atomic Pd, they exhibit Hund's rule magnetism. In long, monostrand nanowires, we find a spin moment of 0.7 mu(B) per atom, whereas for short, monostrand nanowires between bulk leads, the predicted moment is about 0.3 mu(B) per nanowire atom. In contrast, a coaxial (6,1) nanowire was found to be nonmagnetic. The origin of the nanowire magnetism is analyzed.     

Indication of unusual pentagonal structures in atomic-size Cu nanowires

We present a study of the structural and quantum conductance properties of atomic-size copper nanowires generated by mechanical stretching. The atomistic evolution was derived from time-resolved electron microscopy observations and molecular dynamics simulations. We have analyzed the quantum transport behavior by means of conductance measurements and theoretical calculations. The results suggest the formation of an unusual and highly stable pentagonal Cu nanowire with a diameter of approximately 0.45 nm and approximately 4.5 conductance quanta.     

Influence of laser light on electronic transport through atomic-size contacts

This Letter reports on the influence of laser irradiation onto the electrical conductance of gold nanocontacts established with the mechanically controllable break-junction technique. We concentrate on the study of reversible conductance changes which can be as high as 200%. We investigate the dependence on the initial conductance of the contacts, and on the wavelength, the intensity, and the position of the laser spot with respect to the sample. Under most conditions an enhancement of the conductance is observed. Several physical mechanisms which might contribute to the observed effect including thermal expansion, rectification, plasmon excitation, and photon-assisted transport are discussed, among which the two latter ones are most likely the dominating ones.     

Young-type experiment using a single-electron source and an independent atomic-size two-center interferometer

Evidence is given for Young-type interferences caused by a single electron acting on a given double-center scatterer analogous to an atomic-size double-slit system. The electron is provided by autoionization of a doubly excited He atom following the capture of the electrons of H2 by a He2+ incoming ion. The autoionizing projectile is a single-electron source, independent of the interferometer provided by the two H+ centers of the fully ionized H2 molecule. This experiment resembles the famous thought experiment imagined by Feynman in 1963, in which the quantum nature of the electron is illustrated from a Young-like double-slit experiment. Well-defined oscillations are visible in the angular distribution of the scattered electrons, showing that each electron interferes with itself.     

Metallic bonds in clusters

It is stressed that the characters of interatomic bonds in metals change somewhat with the size and geometry of clusters. This change reacts directly on the equilibrium configurations. Specific effects related to electron correlations are less marked than for more electropositive elements.     

Chaos in Josephson junctions

A detailed analysis of the control space characterization of phase locked states and chaotic attractors in Josephson junctions is presented, based on a model that includes both quadratic damping and cosine interference terms. In addition, some novel features of the nonlinear characteristics of the junction like evolution of basin boundaries, bifurcation structure analysis and scaling behaviour of Lyapunov exponent are discussed.     

Photocurrents in nanotube junctions

Photocurrents in nanotube p-n junctions are calculated using a nonequilibrium Green function quantum transport formalism. The short-circuit photocurrent displays band-to-band transitions and photon-assisted tunneling, and has multiple sharp peaks in the infrared, visible, and ultraviolet. The operation of such devices in the nanoscale regime leads to unusual size effects, where the photocurrent scales linearly and oscillates with device length. The oscillations can be related to the density of states in the valence band, a factor that also determines the relative magnitude of the photoresponse for different bands.     

Metallic superlattices

Multilayered metal films with artificial superstructures are prepared by alternate deposition of two elements in ultrahigh vacuum. Preparation and characterization for Fe-Mg and Fe-V superlattices are described. From hyperfine field measurements, chemical profiles of interfaces are discussed. Magnetic properties of extremely thin Fe layers sandwiched in between Mg layers are studied by means of Mőssbauer absorption spectroscopy.     

Influence of coupling between junctions on breakpoint current in intrinsic Josephson junctions

We study theoretically the current-voltage characteristics of intrinsic Josephson junctions in high-Tc superconductors. An oscillation of the breakpoint current on the outermost branch as a function of coupling alpha and dissipation beta parameters is found. We explain this oscillation as a result of the creation of longitudinal plasma waves at the breakpoint with different wave numbers. We demonstrate the commensurability effect and predict a group behavior of the current-voltage characteristics for the stacks with a different number of junctions. A method to determine the wave number of longitudinal plasma waves from alpha and beta dependence of the breakpoint current is suggested. We model the alpha and beta dependence of the breakpoint current and obtain good agreement with the results of the simulation.     

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.     

Electron tunneling in metal-Ge-metal junctions

The phonon peaks in Ge have been observed and identified using electron tunneling experiments with metal-Ge-metal junctions.     

Inelastic tunneling in Al-AlN-Pb junctions

The technique of the prepagation of the tunnel junctions with a barrier made of AlN has been presented. To produce a barrier layer a freshly evaporated Al film was exposed to a glow discharge in atmosphere of pure ammonia. The features shown in the tunnel spectra of these junctions have been interpreted as AlN optic phonons and a vibration spectrum of NH₃ molecules adsorbed in the junctions.     

Contact interference in molecular junctions

We highlight a new manifestation of quantum interference in transport through single-molecule junctions, owing to different charge transport pathways from the molecule through the contacts into the three-dimensional electrode. Such contact interference can be identified with characteristic features of the current–voltage curve, as dramatic as closing an otherwise open transport channel. Based on analysis of the necessary conditions for observation of this phenomenon, we conclude that this effect should be detectable in relatively small molecules, where a molecular site shares coupling to two electrodes, and an electrode surface site shares coupling to different molecular sites. The importance of the surface-molecule connectivity scheme implies that commonly used reduced models which couple different molecular sites to effectively independent electrodes, fail to account for this effect and must be corrected in order to properly capture contact interference.