Observation of quantum supershells in clusters of sodium atoms

Pedersen, Jack K.; Bjørnholm, S.; Borggreen, J.; Hansen, Klavs; Martin, T. P.; Rasmussen, H. D.

doi:10.1038/353733a0

Cited by 252 publications

(154 citation statements)

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“…6 have already been seen previously without any fine tuning of K 0 [12,13,35]. The peak at N = 640 is the only case where a peak, previously thought to be a single spherical shell closing, splits into two.…”

Section: Comparison With Experimentsmentioning

confidence: 58%

“…2). Note that the duster deformations reduce to some extent, but do not abolish, the 'supershell' structure found both in theoretical calculations [6,34] and in experiment [35]. They reduce the total energies in the regions of deformed clusters -and hereby also smear out some of the fine structure found in spherical calculations due to the filling of subshells -but have no effect near the spherical magic numbers where the shell effects are most pronounced.…”

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confidence: 77%

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Modified Nilsson model for large sodium clusters

Reimann

Brack

Hansen³

1993

Z Phys D - Atoms, Molecules and Clusters

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Abstract. We propose a modified Nilsson model for spheroidal sodium clusters and investigate the modification of shell structure by deformation for sizes up to N = 850. For spherical clusters, our potential is fitted to the single-particle spectra obtained from microscopically selfconsistent Kohn-Sham calculations using the jellium model and the local density approximation. Employing Strutinsky's shell-correction method, the surface energy of the jetlium model is renormalized to its experimental value. We find good agreement between our theoretically predicted deformed magic numbers and the experimentally observed ones extracted from recent sodium mass abundance spectra.

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Section: Comparison With Experimentsmentioning

confidence: 58%

mentioning

confidence: 77%

Modified Nilsson model for large sodium clusters

Reimann

Brack

Hansen³

1993

Z Phys D - Atoms, Molecules and Clusters

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“…This periodicity suggests a comparison of our experimental results with the magic numbers observed for sodium clusters. In the cluster experiments, a remarkable structure was observed in the distribution of cluster sizes produced in a supersonic expansion of sodium metal vapour [3,[9][10][11][12][13]. In the spectrum of the abundance versus the number of atoms, N , in the cluster, distinct maxima are observed for N = 2, 8, 20, 40, 58, 92, ....…”

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confidence: 98%

Observation of Shell Structure in Sodium Nanowires

Yanson

Ruitenbeek

2000

Statistical and Dynamical Aspects of Mesoscopic Systems

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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 [1], 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 [2][3][4]. 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 for the electronic shell-closure effects, similar to the abundance peaks at 'magic numbers' of atoms in metal clusters [3,4].Metallic constrictions, in the form of nanowires connecting two bulk metal electrodes, have recently been studied down to sizes of a single atom in cross section by means of scanning tunnelling microscopy (STM) and mechanically controllable break-junctions (MCB) [5,6]. By indenting one electrode into another and then separating them, a stepwise decrease in electrical conductance is observed, down to the breakpoint when arriving at the last atom. Each scan of the dependence of conductance G on the elongation d is individual in detail, as the atomic configuration of each contact may be widely different. However, statistically, many scans together produce a histogram of the probability for observing a given conductance value, which is quite reproducible for a given metal and for fixed experimental parameters.A simple description of the electronic properties of metallic nanowires is expected to work best for monovalent free-electron-like metals. The alkali metals are most suitable, as the bulk electronic states are very well described by free particles in an isotropic homogeneous positive background. In a previous experiment on sodium point contacts [7] a histogram was obtained, which showed pronounced peaks near 1, 3, 5 and 6 times the quantum unit of conductance, G 0 = 2e 2 /h (where e is the charge on an electron and h is Planck's constant). This is exactly the series of quantum numbers expected for the conductance through an ideal cylindrical conductor. We have now extended these experiments to higher temperatures and a much wider range of conductance values.The MCB technique [6] was adapted for the study of nanowires of the highly reactive alkali metals following Ref. [7] (see Fig. 1). Scans were taken continuously by ramping the displacement d of the electrodes with respect to each other, using the piezo-electric driver. Each individual curve of conductance versus displacement, G(d), was recorded in ∼0.1 seconds from the highest conductance into the tunnelli...

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“…The mass spectrometry is well adapted to obtain a global insight as a function of the size. In principle, most intense clusters in the mass spectrum are the most stable and this method has been applied with success to sodium clusters [17,18].…”

Section: Near Threshold Photoionization Electronic Shells and Supersmentioning

confidence: 99%