Two-dimensional CrI3 has attracted much attention as it is reported to be a ferromagnetic semiconductor with the Curie temperature around 45K.By performing first-principles calculations, we find that the magnetic ground state of CrI 3 is variable under biaxial strain. Our theoretical investigations show that the ground state of monolayer CrI3 is ferromagnetic under compression, but becomes antiferromagnetic under tension. Particularly, the transition occurs under a feasible in-plane strain around 1.8%. Accompanied by the transition of the magnetic ground state, it undergoes a transition from magnetic-metal to half-metal to halfsemiconductor to spin-relevant semiconductor when strain varies from -15% to 10%. We attribute these transitions to the variation of the dorbitals of Cr atoms and the p-orbitals of I atoms. Generally, we report a series of magnetic and electronic phase transition in strained CrI 3 , which will help both theoretical and experimental researchers for further understanding of the tunable electronic and magnetic properties of CrI 3 and their analogous.

Van der Waals heterostructures stacked from different two-dimensional materials offer a unique platform for addressing many fundamental physics and construction of advanced devices. Twist angle between the two individual layers plays a crucial role in tuning the heterostructure properties. Here we report the experimental investigation of the twist angle-dependent conductivities in MoS2/graphene van der Waals heterojunctions. We found that the vertical conductivity of the heterojunction can be tuned by ∼5 times under different twist configurations, and the highest/lowest conductivity occurs at a twist angle of 0°/30°. Density functional theory simulations suggest that this conductivity change originates from the transmission coefficient difference in the heterojunctions with different twist angles. Our work provides a guidance in using the MoS2/graphene heterojunction for electronics, especially on reducing the contact resistance in MoS2 devices as well as other TMDCs devices contacted by graphene.

Dodecagonal bilayer graphene quasicrystal has 12-fold rotational order but lacks translational symmetry which prevents the application of band theory. In this paper, we study the electronic and optical properties of graphene quasicrystal with large-scale tight-binding calculations involving more than ten million atoms. We propose a series of periodic approximants which reproduce accurately the properties of quasicrystal within a finite unit cell. By utilizing the band-unfolding method on the smallest approximant with only 2702 atoms, the effective band structure of graphene quasicrystal is derived. Novel features, such as the emergence of new Dirac points (especially the mirrored ones), the band gap at M point and the Fermi velocity are all in agreement with recent experiments. The properties of quasicrystal states are identified in the Landau level spectrum and optical excitations. Importantly, our results show that the lattice mismatch is the dominant factor determining the accuracy of layered approximants. The proposed approximants can be used directly for other layered materials in honeycomb lattice, and the design principles can be applied for any quasi-periodic incommensurate structures.

Pure spin-current is of central importance in spintronics. Here we propose a two-dimensional (2D) spinbattery system that delivers pure spin-current without an accompanying charge-current to the outside world at zero bias. The principle of the spin-battery roots in the photogalvanic effect (PGE), and the system has good operational stability against structural perturbation, photon energy and other materials detail. The device principle is numerically implemented in the 2D material phosphorene as an example, and first principles calculations give excellent qualitative agreement with the PGE physics. The 2D spin-battery is interesting as it is both a device that generates pure spin-currents, also an energy source that harvests photons. Given the versatile operational space, the spin-battery should be experimentally feasible. 72.15.Gd, 71.15.Mb NOTE: This article has been published in Physical Review Applied in a revised form (

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The electronic structures of 30 • twisted double bilayer graphene, which loses the translational symmetry due to the incommensurate twist angle, are studied by means of the tight-binding approximation. We demonstrate the interlayer decoupling across the 30 • twisted interface in the vicinity of the Fermi level from various electronic properties, including the density of states, effective band structure, optical conductivity, and Landau-level spectrum. However, at Q points, the interlayer coupling results in the appearance of new Van Hove singularities in the density of states, new peaks in the optical conductivity and, importantly, the 12-fold-symmetry-like electronic states. The k-space tight-binding method is adopted to explain this phenomenon. The electronic states at Q points show charge distribution patterns more complex than the 30 • twisted bilayer graphene due to the symmetry decrease. These phenomena also appear in the graphene monolayer on the AB-stacked graphene bilayer with a 30 • twist angle.

The first observation of surface metallization of TiO 2Àx induced by fluoride ions is presented. The emerging metallic states are contributed by the 3d orbital of surface Ti and the 2p orbital of surface bridging F, which are intrinsically originated from the strong electron repulsion between F À and adjacent Ti 3+ . The metalized TiO 2Àx with reduced work function and downward band bending possesses high electron-donating power to supported Ru species via atomic-scale ohmic contacts, exhibiting unprecedented photocatalytic performances for ammonia synthesis across the entire solar spectrum region (200-1550 nm) at room temperature. Mechanism and kinetic analysis revealed that the loaded Ru could behave as efficient electron sinks to accumulate photogenerated electrons and that the metallic surface markedly enhanced the dissociation of H 2 and N 2 by the hot electrons generated by the visible or even infrared light irradiation.

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