Superatom
Superatomic crystals are typically prepared by combining structurally and electronically complementary superatoms in solution. Various tuneable molecular clusters can be used as superatomic building blocks, and by using different assembly motifs, these blocks can be assembled into materials. [Superatoms in materials science]
Atomic clusters, consisting of a few to a few thousand atoms, have emerged over the past 40 years as the ultimate nanoparticles. Some of these clusters form stable units with atomically precise structures that give rise to collective behaviors that mimic those of traditional atoms, essentially functioning as ‘superatoms’[1, 2]. The ultimate vision is to create materials with tailored and tuneable functions through the judicious design, synthesis and assembly of superatoms. The use of superatoms as building blocks for materials offers opportunities to design materials with tailored functionalities[3, 4].
Graphullerene, a two-dimensional crystalline polymer of C60, bridges the gulf between molecular and extended carbon materials. Its constituent fullerene subunits arrange hexagonally in a covalently interconnected molecular sheet.
Endohedral silicon cage V@Si12 clusters can construct two types of single cluster sheets exhibiting hexagonal porous or honeycomb-like framework with regularly and separately distributed V atoms. For the ground state of these two sheets, the preferred magnetic coupling is found to be ferromagnetic due to a free-electrons mediated mechanism. By using external strain, the magnetic moments and strength of magnetic coupling for these two sheets can be deliberately tuned, which would be propitious to their advanced applications.
However, the reinforcing chemical interaction between atoms (chemical bond)[5, 6]is the main factor that leads to the unstable structure of atomic crystal through the replacement of elements, and the weakening of such interaction is likely to overcome this difficulty. In the superatomic crystal materials with atomic clusters as the basic building unit, the surface saturated atomic clusters can be combined by non-covalent interactions such as weak atom identification, electrostatic interaction[7] and hydrogen bonding[8]. It has the potential to maintain structural stability in the regulation of electronic structural properties through continuous cluster (element) replacement, and is also more in line with the needs of large-scale material preparation, with some characteristics of atomic fabrication.
AuTeSe
Fig.1 Intercube Te-Te quasibonds and two interweaved charge orders in the ATS superatomic crystal
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Physical review X
Interweaving Polar Charge Orders in a Layered Metallic Super-atomic Crysta
A superatom is any cluster of atoms that collectively exhibits some properties of single atoms. When arranged into crystals through the noncovalent bonds, they can be readily assembled into nanostructures, because the reduced cohesive energy of the noncovalent bonds makes it easier to cleave the material. It is not yet clear whether such weakened energetic interaction is accompanied by a suppressed electronic interaction among the superatoms. To that end, we explore exotic electronic structures on the surface of one superatomic crystal and find strong electron-electron interactions do occur. We also find that two exotic charge orders emerge.
Recently, researchers synthesized a cubic superatom, Au6Te12Se8 (ATS), and assembled it into a 3D crystal with metallicity and superconductivity.[9] In our experiments, we observe two charge orders on the ATS surface. One is a charge density wave that forms across repeating columns of ATS cubes. The other is a polar metallic state that arises between the columns. The polar metallic states are of particular interest, suggesting the ATS surface is an antipolar metal—a type of exotic metal where metallicity and orderly, antiparallel-oriented electric dipoles coexist. The discovery of this antipoloar metal goes one step further toward the realization of multifunctional devices, which could, in principle, perform simultaneous electrical, magnetic, and optical functions. However, we have not yet examined ATS’s ferroelectricity, which is needed for electrical control of its electrical polarization.
This ATS crystal is, to the best of our knowledge, the first antipolar metal ever found and possesses the first polar metallic state hosted in superatomic units bound by noncovalent interactions. Thus, the strong electron-electron interactions, found in the 2D superatomic layers, open a category of quantum materials that contains versatile layered nanostructures exhibiting precisely tailorable electronic structures.
1. Z. Luo, A.W. Castleman, Special and General Superatoms, Accounts of Chemical Research 47 (2014) 2931-2940
2. Superatoms: Electronic and Geometric Effects on Reactivity, (2017)
3. E.A. Doud, A. Voevodin, T.J. Hochuli, A.M. Champsaur, C. Nuckolls, X. Roy, Superatoms in materials science, Nature Reviews Materials 5 (2020) 371-387
4. J. Puru, S. Qiang, Super Atomic Clusters: Design Rules and Potential for Building Blocks of Materials, Chemical Reviews 118 (2018) acs.chemrev.7b00524-
5. Z. Liu, X. Wang, J. Cai, H. Zhu, Room-Temperature Ordered Spin Structures in Cluster-Assembled Single V@Si12 Sheets, The Journal of Physical Chemistry C (2014)
6. E. Meirzadeh, A.M. Evans, M. Rezaee, M. Milich, C.J. Dionne, T.P. Darlington, S.T. Bao, A.K. Bartholomew, T. Handa, D.J. Rizzo, R.A. Wiscons, M. Reza, A. Zangiabadi, N. Fardian-Melamed, A.C. Crowther, P.J. Schuck, D.N. Basov, X. Zhu, A. Giri, P.E. Hopkins, P. Kim, M.L. Steigerwald, J. Yang, C. Nuckolls, X. Roy, A few-layer covalent network of fullerenes, Nature 613 (2023) 71-76
7. Evan, S., O’Brien, M., Tuan, Trin, Rose, L., Kann, Jia, Single-crystal-to-single-crystal intercalation of a low-bandgap superatomic crystal, Nature Chemistry (2017)
8. H. Yang, W. Yu, H. Huang, L. Gell, L. Lehtovaara, S. Malola, H. Hkkinen, N. Zheng, All-thiol-stabilized Ag44 and Au12Ag32 nanoparticles with single-crystal structures, Nature Publishing Group (2013)
9. Guo, J.G., Chen, X., Jia, X.Y. et al. Quasi-two-dimensional superconductivity from dimerization of atomically ordered AuTe2Se4/3 cubes. Nat Commun 8, 871 (2017)
Ji Group@Renmin University