A Novel Feature in Aluminum Cluster Photoionization Spectra and Possibility of Electron Pairing at <i>T</i> ≳ 100 K

Halder, Avik; Liang, Anthony; Kresin, Vladimir Z.

doi:10.1021/nl5048175

Cited by 28 publications

(19 citation statements)

References 38 publications

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“…In many-fermion systems like clusters and atomic nuclei an interesting common aspect is that fermions couple and form pairs that are responsible for collective behavior, involving one or more pairs of nucleons (for atomic nuclei) or electrons (for clusters, molecules, and superconductors). There have been several studies invoking BCS mechanisms to predict superconducting behavior in (networks of) atomic clusters, so far with limited experimental evidence [43]. But manifestations that may relate to electron pairing, e.g., odd-even effects in experiments, are ubiquitous.…”

Section: Discussionmentioning

confidence: 99%

Thermal radiation of gold clusters on microsecond time scales

et al. 2017

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Small positively charged gold clusters have been found to emit thermal radiation at a very high rate, with time constants ranging from one to 35 μs for Au n + (n = 6-13,15). For sizes n = 14,16-20 the radiation occurs on much longer time scales. Strong thermal suppression of the population of higher-lying states puts constraints on the possible energies of excited states that can contribute to the radiation. Taking that into account, an evaluation of the experimentally determined rate constants shows that the strong radiation originates from thermally excited low-lying electronic states hitherto not observed. The origin of these states is discussed and two possibilities are suggested: one is related to electron correlation and electron pairing, and the other results from thermal shape fluctuations.

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Section: Discussionmentioning

confidence: 99%

Thermal radiation of gold clusters on microsecond time scales

et al. 2017

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“…The clearest and most prominent example is observed in the photoionization spectrum of the closed-shell [9,10,[46][47][48] "magic" cluster Al 66 with 198 valence electrons, as seen in the progression of spectra shown in Fig. 3(b) [43]. We begin by focusing on this cluster.…”

Section: Temperature-induced Transition In the Spectrummentioning

confidence: 98%

“…An earlier brief report was published in Ref. [43], here we provide a full description of the experimental procedure, and present further results and a detailed discussion.…”

Section: Introductionmentioning

confidence: 94%

“…3(a) [43]. These curves can be put to use for extracting the cluster ionization energies (work functions) and their size and temperature variations [53,54], but they do not display any peculiar features.…”

Section: Temperature-induced Transition In the Spectrummentioning

confidence: 99%

“…5 are based on data analysis procedures described in the Appendix and revised as compared with Ref. [43].) This presentation already suggests that an electronic transition is taking place.…”

Section: Temperature-induced Transition In the Spectrummentioning

confidence: 99%

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

Halder

Kresin

2015

Phys. Rev. B

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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.

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Localization‐vs‐Delocalization of 5f Orbitals in Superatom Systems

Jiang

Wang

2018

Advcd Theory and Sims

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A long-standing debate on the system containing the actinide element is the extent of localization and participation of the 5f orbitals in chemical bonding across the actinide series. Here, we illuminate that the 5f orbitals have both dual nature in superatomic bonding for protactinium, uranium, neptunium, and plutonium using density functional theory. Electronic structure analysis reveals that the partial 5f electrons are active and could be preferentially excited to 6d shells to satisfy jelliumic bonding of the 18-electron rule (1S 2 1P 6 1D 10 ). In contrast, the extra 5f electrons are more localized for neptunium and plutonium compared with protactinium and uranium, and present antiferromagnetic and ferromagnetic couplings for the spin arrangements between actinide atoms and confined gold clusters, and largely localized at the actinide atom. This work offers not only a new recipe for breeding magnetic superatoms, but also is very promising for the designing of superconducting materials and heavy-fermion systems.For a long time, substantial attention has been focused on systems containing the actinide (An) elements. [1][2][3][4] One of the main reasons is that the 5f orbitals can exhibit localization like the 4f orbitals in the lanthanide series, or delocalization (participation) like the d orbitals in the transition metals, or both in the chemical bonding. In fact, the competition has resulted in multiple complicated ground states and phases in compounds and alloy systems. [5,6] Currently, although the degree of localization of 5f electrons has been recognized as the dominant factor in determining the magnetic and electronic properties of the materials, [7,8] experimental methods for measuring the occupancy of 5f electron are still very unsuccessful though some exceptions exist. Therefore, an equally important task is to explore simplified superatomic models containing actinide elements to understand the origin of their properties and enhanced stability.Currently, there are a number of electron counting rules in cluster science that can be effectively utilized in the design and synthesis of materials. [9][10][11][12][13] Among them, 18-electron rule, which is a conceptual extension to the octet rule by the insertion of a metal element with d valence electrons into the closed shell s 2 p 6 (eight electrons), has been regarded as cornerstone for understanding and explaining the transition-metal (especially for the gold clusters) structural stability and physicochemical properties. [14,15] For example, the icosahedral W/Mo@Au 12 cluster was confirmed by theoretical [16] and experimental [17] works, which stability can be attributed to and the 18-electron rule and the strong relativistic effects. Furthermore, the study of M@Au n (M: metal atom of VIIA-IA group; n = 8-17) clusters have shown that at n = 14, the gold-covered bimetallic cluster can achieve the highest binding energy per atom and gap between highest occupied molecular orbital and lowest unoccupied molecular orbital. [18] Therefore, as an important al...

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A Novel Feature in Aluminum Cluster Photoionization Spectra and Possibility of Electron Pairing at T ≳ 100 K

Cited by 28 publications

References 38 publications

Thermal radiation of gold clusters on microsecond time scales

Thermal radiation of gold clusters on microsecond time scales

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

Localization‐vs‐Delocalization of 5f Orbitals in Superatom Systems

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