A novel feature in aluminum cluster photoionization spectra and possibility of electron pairing at T ≳ 100 K.

Halder, Avik; Liang, Anthony; Kresin, Vitaly V · Nano Lett · 2015

basic_science · Level V

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Abstract

A unique property of size-resolved metal nanocluster particles is their "superatom"-like electronic shell structure. The shell levels are highly degenerate, and it has been predicted that this can enable exceptionally strong superconducting-type electron pair correlations in certain clusters composed of just tens to hundreds of atoms. Here we report on the observation of a possible spectroscopic signature of such an effect. A bulge-like feature appears in the photoionization yield curve of a free cold aluminum cluster and shows a rapid rise as the temperature approaches ≈100 K. This is an unusual effect, not previously reported for clusters. Its characteristics are consistent with an increase in the effective density of states accompanying a pairing transition, which suggests a high-temperature superconducting state with Tc ≳ 100 K. Our results highlight the promise of metal nanoclusters as high-Tc building blocks for materials and networks.