Electrons in metal clusters organize into quantum shells, akin to atomic shells in the periodic table. Such nanoparticles are referred to as “superatoms”. The electronic shell levels are highly degenerate giving rise to sharp peaks in the density of states, which can enable exceptionally strong electron pairing in certain clusters containing tens to hundreds of atoms.
A spectroscopic investigation of size – resolved aluminum nanoclusters has revealed a sharp rise in the density of states near the Fermi level as the temperature decreases towards 100 K. The effect is especially prominent in the closed-shell “magic” cluster Al66 [1, 2]. The characteristics of this behavior are fully consistent with a pairing transition, implying a high temperature superconducting state with Tc < 100K. This value exceeds that of bulk aluminum by two orders of magnitude.
As a new class of high-temperature superconductors, such metal nanocluster particles are promising building blocks for high-Tc materials, devices, and networks.
1. Halder, A., Liang, A., Kresin, V. V. A novel feature in aluminum cluster photoionization spectra and possibility of electron pairing at T 100K. Nano Lett 15, 1410 – 1413 (2015)
2. Halder, A., Kresin, V. V. A transition in the density of states of metal “superatom” nanoclusters and evidence for superconducting pairing at T 100K. Phys. Rev. B 92, 214506 (2015).
Avik Halder and Vitaly V. Kresin, "Nanoclusters as a new family of high temperature superconductors (Conference Presentation)," Proc. SPIE 10105, Oxide-based Materials and Devices VIII, 1010507 (Presented at SPIE OPTO: January 29, 2017; Published: 19 April 2017); https://doi.org/10.1117/12.2266156.5393342264001.
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