title: A novel feature in aluminum cluster photoionization spectra and possibility of electron pairing at T ≳ 100 K.
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.
authors: Department of Physics and Astronomy, University of Southern California , Los Angeles, California 90089-0484, United States.
authors: Avik
authors: A
authors: Halder
authors: Anthony
authors: A
authors: Liang
authors: Vitaly V
authors: VV
authors: Kresin
keywords: Metal nanoclusters; electronic shell structure; photoionization and photoemission spectroscopy; superconducting pairing