Interaction-induced beats of Friedel oscillations in quantum wires.

We analyze the spectrum of electron density oscillations in an interacting one-dimensional electron system with an impurity. The system's inhomogeneity is characterized by different values of Fermi wave vectors kF=k L/R on left or right side of the scatterer, leading to a Landauer dipole formation. We demonstrate, that while in the noninteracting system the Friedel oscillations possess only one periodicity related to the local kF, say kL on the left side, the interplay of the interactions and the Landauer dipole generates an additional peak in the spectrum of density oscillations at the counterpart kR. Being only present in correlated systems, the position and shape of this spectral feature, which in coordinate space is observable as a beating pattern in the Friedel oscillations, reveals many important details about the nature of interactions. Thus it has a potential to become an investigation tool in condensed matter physics.

Electronic and atomic shell structure in aluminium nanowires.

We report experiments on aluminium nanowires in ultra-high vacuum at room temperature that reveal a periodic spectrum of exceptionally stable structures. Two 'magic' series of stable structures are observed: at low conductance, the formation of stable nanowires is governed by electronic shell effects whereas for larger contacts atomic packing dominates. The crossover between the two regimes is found to be smooth. A detailed comparison of the experimental results to a theoretical stability analysis indicates that, while the main features of the observed electron-shell structure are similar to those of alkali and noble metals, a sequence of extremely stable wires plays a unique role in aluminium. This series appears isolated in conductance histograms and can be attributed to 'superdeformed' non-axisymmetric nanowires.

Jahn-Teller distortions and the supershell effect in metal nanowires.

A stability analysis of metal nanowires shows that a Jahn-Teller deformation breaking cylindrical symmetry can be energetically favorable, leading to stable nanowires with elliptic cross sections. The sequence of stable cylindrical and elliptical nanowires allows for a consistent interpretation of experimental conductance histograms for alkali metals, including both the electronic shell and supershell structures. It is predicted that for gold, elliptical nanowires are even more likely to form since their eccentricity is smaller than for alkali metals. The existence of certain metastable superdeformed nanowires is also predicted.

Interplay of Rayleigh and Peierls instabilities in metallic nanowires.

A quantum-mechanical stability analysis of metallic nanowires within the free-electron model is presented. The stability is determined by an interplay of electron-shell effects, the Rayleigh instability due to surface tension, and the Peierls instability. Although the latter effect limits the maximum length also for wires with "magic radii," it is found that nanowires in the micrometer range can be stable at room temperature.