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Recent studies have revealed the potential of 2D moiré superlattices as a condensed matter quantum simulator. The realization of different lattice model Hamiltonians in moiré superlattices has become the focus of researches. Here, it shows that, compared to bilayer moiré superlattices where there is only one interface, the interference between moiré patterns at different interfaces in 2D multilayer structures allows the physical realization of more complicated lattice models. The concept is demonstrated by trilayer moiré superlattices (TMSLs) of MoS2, where it finds that isolated flat moiré bands appear near the valence band edge, and they can be described by the honeycomb lattice ionic Hubbard model. More importantly, the hopping strength, the on‐site Coulomb repulsion, and the staggered potential in the TMSLs are highly tunable through the control of the twist angle, the dielectric environment, and the perpendicular electric field. It is possible to achieve various transitions between distinct quantum phases in the TMSLs, spanning from weak to strong correlation regimes. Therefore, the proposed TMSLs can serve as a good platform to study the strong correlation physics in the honeycomb lattice ionic Hubbard model. [ABSTRACT FROM AUTHOR]

The core task for Mott insulators includes how rigid distributions of electrons evolve and how these induce exotic physical phenomena. However, it is highly challenging to chemically dope Mott insulators to tune properties. Herein, we report how to tailor electronic structures of the honeycomb Mott insulator RuCl3 employing a facile and reversible single‐crystal to single‐crystal intercalation process. The resulting product (NH4)0.5RuCl3⋅1.5 H2O forms a new hybrid superlattice of alternating RuCl3 monolayers with NH4+ and H2O molecules. Its manipulated electronic structure markedly shrinks the Mott–Hubbard gap from 1.2 to 0.7 eV. Its electrical conductivity increases by more than 103 folds. This arises from concurrently enhanced carrier concentration and mobility in contrary to the general physics rule of their inverse proportionality. We show topotactic and topochemical intercalation chemistry to control Mott insulators, escalating the prospect of discovering exotic physical phenomena. [ABSTRACT FROM AUTHOR]

The core task for Mott insulators includes how rigid distributions of electrons evolve and how these induce exotic physical phenomena. However, it is highly challenging to chemically dope Mott insulators to tune properties. Herein, we report how to tailor electronic structures of the honeycomb Mott insulator RuCl3 employing a facile and reversible single‐crystal to single‐crystal intercalation process. The resulting product (NH4)0.5RuCl3⋅1.5 H2O forms a new hybrid superlattice of alternating RuCl3 monolayers with NH4+ and H2O molecules. Its manipulated electronic structure markedly shrinks the Mott–Hubbard gap from 1.2 to 0.7 eV. Its electrical conductivity increases by more than 103 folds. This arises from concurrently enhanced carrier concentration and mobility in contrary to the general physics rule of their inverse proportionality. We show topotactic and topochemical intercalation chemistry to control Mott insulators, escalating the prospect of discovering exotic physical phenomena. [ABSTRACT FROM AUTHOR]

Herein, the crystalline and electronic structures of ultrathin cadmium sulfide {0001} films with thickness ranging from 1 to 14 Cd–S bilayers are studied using first‐principles calculations method. After structural relaxation, the film composed of 1 Cd–S bilayer is transformed into a CdS monolayer with flat honeycomb structure. Those 2‐ to 5‐bilayer films do not maintain the Wurtzite structure either: the distance between the sulfur and cadmium layers in each bilayer is compressed while the Cd–S bond length between adjacent bilayers is enlarged. These 1‐ to 5‐bilayer films reveal semiconducting characteristics in band structures, and their bandgaps are widened in some degree compared with the bulk. The films with 6–14 Cd–S bilayers keep the Wurtzite structure of the bulk, and exhibit metallic surface states due to the polarity of the films. The results could provide a new insight for the electronic structure regulation of cadmium sulfide. [ABSTRACT FROM AUTHOR]

In this work, the rational design of O′3‐type Na[Ni2/3−xCoxSb1/3]O2, a solid solution of Na[Ni2/3Sb1/3]O2–Na[Co2/3Sb1/3]O2, is introduced. Because of the difficulty of the Co3+/2+ redox reaction, the electronic structures of Na[Ni2/3−xCoxSb1/3]O2 compounds are engineered to build electroconducting networks in the oxide matrix through electrochemical oxidation of Co2+ to Co3+, after which the formed Co3+ does not participate in the electrochemical reaction but improves the electrical conductivity in the structure. Density functional theory calculations reveal a reduced bandgap energy after the formation of Co3+ during desodiation of Na1−y[Ni2/3−xCoxSb1/3]O2. Using the oxidized Co3+ species while improving the electrical conductivity, the Na[Ni2/3−xCoxSb1/3]O2 (x = 1/6) electrode exhibits excellent cyclability for 1000 cycles with ≈72.5% capacity retention at 2C (400 mA g−1) and activity even at 50C (10 A g−1) in Na cells. Operando X‐ray diffraction and ex situ X‐ray absorption near‐edge structure investigations reveal suppressed lattice variations upon charge and discharge compared with those of Na[Ni2/3Sb1/3]O2 achieved by the presence of the electrochemical‐driven Co3+ in the structure. These findings offer a new strategy for the development of cathode materials for sodium‐ion batteries, providing important insight into their structural transformations and the electronic nature of advanced cathode materials. [ABSTRACT FROM AUTHOR]

Threefold symmetric triperyleno[3.3.3]propellanes (TPRPs), which are composed of three perylene units peri‐fused on [3.3.3]proppellane, have been synthesized and their electronic properties characterized. Unsubstituted TPRP assembles into two‐dimensional honeycomb‐like networks. TPRP displays a bathochromic‐shifted absorption band in its absorption spectrum and shows well‐separated one‐electron redox waves in a cyclic voltammogram, due to a homoconjugative interaction between perylene moieties. A radical cation species of tert‐butyl substituted TPRP shows spin delocalization over the whole of the molecule, which is derived from effective overlap of HOMOs among three perylene moieties. [ABSTRACT FROM AUTHOR]

Quasi two-dimensional (2D) oxide-based honeycomb lattices have attracted great attention for displaying specific electronic instabilities, which give rise to unconventional bonding patterns and unexpected magnetic exchange couplings. The synthesis of AgRuO3, another representative exhibiting unique structural properties, is reported here. The stacking sequence of the honeycomb layers (Ru2O6) differs from analogous precedents; in particular, the intercalating silver atoms are shifted from the middle of the interspaces and cap the void octahedral sites of the (□Ru2O6) slabs from both sides. This way, charge neutral, giant 2D 'molecules' of Ag/Ru2O6/Ag result; a feature that significantly enhances the overall 2D character of AgRuO3. Measurements of magnetization have revealed extremely strong magnetic exchange coupling to be present, surviving to a temperature as high as 673 K, which is the temperature of thermal decomposition. No indication for long-range magnetic order has, however, been observed. Theoretical analyses confirm the pronounced 2D character of the electronic system, and in particular reveal the inter-honeycomb layer coupling Jc to be distinctly weak. [ABSTRACT FROM AUTHOR]

We have designed novel two-dimensional (2D) carbon allotropes consisting of the small fullerene C26 using first-principles total energy calculations based on the density functional theory. We found that the fused C26 polyhedra form a periodic 2D honeycomb covalent net-work. The initial honeycomb network converted into two different stable structures upon structural optimization. Both phases were found to be energetically stable, and the calculated total energies were found to be 0.6 eV/atom higher than the energy of diamond. The electronic structures of the two fused C26 networks were found to be metals, and one of the structures possesses linear dispersion bands near the Fermi level, owing to the formation of a one-dimensional fused octagonal sp2 network on the polymeric layer. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]