I. K. Yanson

Observation of Shell Structure in Sodium Nanowires

The quantum states of a system of particles in a finite spatial domain in general consist of a set of discrete energy eigenvalues; these are usually grouped into bunches of degenerate or close-lying levels, called shells. In fermionic systems, this gives rise to a local minimum in the total energy when all the states of a given shell are occupied. In particular, the closed-shell electronic configuration of the noble gases produces their exceptional stability. Shell effects have previously been observed for protons and neutrons in nuclei, and for clusters of metal atoms. Here we report the observation of shell effects in an open system—a sodium metal nanowire connecting two bulk sodium metal electrodes, which are progressively pulled apart. We measure oscillations in the statistical distribution of conductance values, for contact cross-sections containing up to a hundred atoms or more. The period follows the law expected from shell-closure effects, similar to the abundance peaks at ‘magic’ numbers of atoms in metal clusters,.

Supershell Structure in Alkali Metal Nanowires

Nanowires are formed by indenting and subsequently retracting two pieces of sodium metal. Their cross section gradually reduces upon retraction and the diameters can be obtained from the conductance. In previous work we have demonstrated that when one constructs a histogram of diameters from large numbers of indentation-retraction cycles such histograms show a periodic pattern of stable nanowire diameters due to shell structure in the conductance modes. Here, we report the observation of a modulation of this periodic pattern, in agreement with predictions of a supershell structure.

Atomic size oscillations in conductance histograms for gold nanowires and the influence of work hardening

Nanowires of different natures have been shown to self-assemble as a function of stress at the contact between two macroscopic metallic leads. Here we demonstrate for Au wires that the balance between various metastable nanowire configurations is influenced by the microstructure of the starting materials, and we discover a new set of periodic structures, which we interpret as due to the atomic discreteness of the contact size for the three principal crystal orientations.

Crossover from Electronic to Atomic Shell Structure in Alkali Metal Nanowires

After making a cold weld by pressing two clean metal surfaces together, upon gradually separating the two pieces a metallic nanowire is formed, which progressively thins down to a single atom before contact is lost. In previous experiments we have observed that the stability of such nanowires is influenced by electronic shell filling effects, in analogy to shell effects in metal clusters. For sodium and potassium at larger diameters there is a crossover to crystalline wires with shell closings corresponding to the completion of additional atomic layers. This observation completes the analogy between shell effects observed for clusters and nanowires.

Aluminum nanowires : Influence of work hardening on conductance histograms

Conductance histograms of work-hardened Al show a series up to 11 equidistant peaks with a period of

Shell effects in alkali metal nanowires

1.15ifmmodepmelsetextpmfi{}0.02

Reconstruction of the electron-phonon interaction function in Ta, 2H-NbSe2 and MgB2 from spectra of S–c–N microcontacts

of the quantum conductance unit

Characterization of point-contacts showing size-effect in electron scattering by magnetic impurities

{G}_{0}=2{e}^{2}∕h

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

. Assuming that the peaks originate from atomic discreteness, this agrees with the value of 1.16

One atom point contacts.

{G}_{0}