Spectroscopy of metal “superatom” nanoclusters and high-Tcsuperconducting pairing

Abstract

A unique property of metal nanoclusters is the "superatom" shell structure of their delocalized electrons.The electronic shell levels are highly degenerate and therefore represent sharp peaks in the density of states. This can enable exceptionally strong electron pairing in certain clusters composed of tens to hundreds of atoms. In a finite system, such as a free nanocluster or a nucleus, pairing is observed most clearly via its effect on the energy spectrum of the constituent fermions. Accordingly, we performed a photoionization spectroscopy study of size-resolved aluminum nanoclusters and observed a rapid rise of the near-threshold density of states of several clusters (Al 37,44,66,68 ) with decreasing temperature. The characteristics of this behavior are consistent with compression of the density of states by a pairing transition into a high-temperature superconducting state with T c ≳100 K. This value exceeds that of bulk aluminum by two orders of magnitude. These results highlight the potential of novel pairing effects in size-quantized systems and the possibility to attain even higher critical temperatures by optimizing the particles' size and composition. As a new class of high-temperature superconductors, such metal nanocluster particles are promising building blocks for high-T c materials, devices, and networks.

Nanocluster ionization energies and work function of aluminum, and their temperature dependence

“…We briefly outline the experimental approach, which has been described in detail previously [9][10][11]. Neutral Al n clusters are produced by a magnetron sputtering/gas condensation source [12,13].…”

Energetics of charged metal clusters containing vacancies

“…It is known that superconducting correlations depend crucially on the density of states near the Fermi energy. Certain shapes of nanoclusters support highly enhanced density of states near electronic shell closings, see, e.g., recent works [5,6]. For ideal nanoclusters, the highest energy occupied electronic levels become strongly degenerate at spherical shell closings ("magic" numbers).…”

Spin–Orbit Coupling Effects on Ligand-Free Icosahedral Matryoshka Superatoms

“…In the cluster science, the “superatom” is generally a kind of of well-designed clusters which could exhibit some atom-like characteristics. − A great deal of attractive properties could be found for specific superatoms, − and then their enormous potential in massive application fields could be drawn out, such as, the field-effect transistor device, the high- T c superconductivity, , the chemical catalysis, , etc . In addition, the superatoms play a conspicuously important role in the cluster-assembled materials, ,− which has attracted great attentions in the materials science. − Therefore, it is an essential task to search for new superatoms with peculiar structures and novel properties.…”