Superatomic crystals

Superatomic crystals

Superatomic crystals
C60、AuTeSe…

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.

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Ji Group@Renmin University

Correlated 2D layers

Correlated 2D layers
CDW、NbSe2、VSe2…

Correlated two-dimensional (2D) layers exhibit varies quantum phases, e.g. unconventional superconductor[1, 2], quantum spin liquids[3, 4], Mott and charge-transfer (CT) insulators[5-7], charge-density ware (CDW)[8, 9] and Wigner crystals[10-12], have been emerging in correlated systems. The understanding of correlated electronic systems and the phase transitions between those quantum states is very important.

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Ji Group@Renmin University

Frustrated ferromagnetic transition in AB-stacked honeycomb bilayer

Frustrated ferromagnetic transition in AB-stacked honeycomb bilayer

Science Bulletin 67(24), 2557-2563 (2022)

Shiyuan Wang#, Yao Wang#, Shaohua Yan#, Cong Wang#, Bingke Xiang, Keyi Liang, Qiushi He, Kenji Watanabe, Takashi Taniguchi, Shangjie Tian, Hechang Lei, Wei Ji, Yang Qi, Yihua Wang*

Abstract

In two-dimensional (2D) ferromagnets, anisotropy is essential for the magnetic ordering as dictated by the Mermin-Wagner theorem. But when competing anisotropies are present, the phase transition becomes nontrivial. Here, utilizing highly sensitive susceptometry of scanning superconducting quantum interference device microscopy, we probe the spin correlations of ABC-stacked CrBr3 under zero magnetic field. We identify a plateau feature in susceptibility above the critical temperature (�C) in thick samples. It signifies a crossover regime induced by the competition between easy-plane intralayer exchange anisotropy versus uniaxial interlayer anisotropy. The evolution of the critical behavior from the bulk to 2D shows that the competition between the anisotropies is magnified in the reduced dimension. It leads to a strongly frustrated ferromagnetic transition in the bilayer with fluctuation on the order of �C, which is distinct from both the monolayer and the bulk. Our observation demonstrates unconventional 2D critical behavior on a honeycomb lattice.

DOI: 10.1016/j.scib.2022.12.009