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تسجيل مستخدم جديدAnisotropic Moire Optical Transitions in Twisted Monolayer/bilayer Phosphorene Heterostructures
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Moire superlattices of van der Waals heterostructures provide a powerful new way to engineer the electronic structures of two-dimensional (2D) materials. Many novel quantum phenomena have emerged in different moire heterostructures, such as correlated insulators, superconductors, and Chern insulators in graphene systems and moire excitons in transition metal dichalcogenide (TMDC) systems. Twisted phosphorene offers another attractive system to explore moire physics because phosphorene features an anisotropic rectangular lattice, different from the isotropic hexagonal lattice in graphene and TMDC. Here we report emerging anisotropic moire optical transitions in twisted monolayer/bilayer phosphorene. The optical resonances in phosphorene moire superlattice depend sensitively on the twist angle between the monolayer and bilayer. Surprisingly, even for a twist angle as large as 19{deg} the moire heterostructure exhibits optical resonances completely different from those in the constituent monolayer and bilayer phosphorene. The new moire optical resonances exhibit strong linear polarization, with the principal axis lying close to but different from the optical axis of bilayer phosphorene. Our ab initio calculations reveal that the {Gamma}-point direct bandgap and the rectangular lattice of phosphorene, unlike the K-point bandgap of hexagonal lattice in graphene and TMDC, give rise to the remarkably strong moire physics in large-twist-angle phosphorene heterostructures. Our results highlight the exciting opportunities to explore moire physics in phosphorene and other van der Waals heterostructures with different lattice configurations.
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In twisted bilayer graphene (TBG) a moire pattern forms that introduces a new length scale to the material. At the magic twist angle of 1.1{deg}, this causes a flat band to form, yielding emergent properties such as correlated insulator behavior and
superconductivity [1-4]. In general, the moire structure in TBG varies spatially, influencing the local electronic properties [5-9] and hence the outcome of macroscopic charge transport experiments. In particular, to understand the wide variety observed in the phase diagrams and critical temperatures, a more detailed understanding of the local moire variation is needed [10]. Here, we study spatial and temporal variations of the moire pattern in TBG using aberration-corrected Low Energy Electron Microscopy (AC-LEEM) [11,12]. The spatial variation we find is lower than reported previously. At 500{deg}C, we observe thermal fluctuations of the moire lattice, corresponding to collective atomic displacements of less than 70pm on a time scale of seconds [13], homogenizing the sample. Despite previous concerns, no untwisting of the layers is found, even at temperatures as high as 600{deg}C [14,15]. From these observations, we conclude that thermal annealing can be used to decrease the local disorder in TBG samples. Finally, we report the existence of individual edge dislocations in the atomic and moire lattice. These topological defects break translation symmetry and are anticipated to exhibit unique local electronic properties.
Recently, phosphorene electronic and optoelectronic prototype devices have been fabricated with various metal electrodes. We systematically explore for the first time the contact properties of monolayer (ML) phosphorene with a series of commonly used
metals (Al, Ag. Cu, Au, Cr, Ni, Ti, and Pd) via both ab initio electronic structure calculations and more reliable quantum transport simulations. Strong interactions are found between all the checked metals, with the energy band structure of ML phosphorene destroyed. In terms of the quantum transport simulations, ML phosphorene forms a n-type Schottky contact with Au, Cu, Cr, Al, and Ag electrodes, with electron Schottky barrier heights (SBHs) of 0.30, 0.34, 0.37, 0.51, and 0.52 eV, respectively, and p-type Schottky contact with Ti, Ni, and Pd electrodes, with hole SBHs of 0.30, 0.26, and 0.16 eV, respectively. These results are in good agreement with available experimental data. Our findings not only provide an insight into the ML phosphorene-metal interfaces but also help in ML phosphorene based device design.
Strong electron correlation and spin-orbit coupling (SOC) provide two non-trivial threads to condensed matter physics. When these two strands of physics come together, a plethora of quantum phenomena with novel topological order have been predicted t
o emerge in the correlated SOC regime. In this work, we examine the combined influence of electron correlation and SOC on a 2-dimensional (2D) electronic system at the atomic interface between magic-angle twisted bilayer graphene (tBLG) and a tungsten diselenide (WSe) crystal. In such a structure, strong electron correlation within the moire flatband stabilizes correlated insulating states at both quarter and half-filling, whereas SOC transforms these Mott-like insulators into ferromagnets, evidenced by robust anomalous Hall effect with hysteretic switching behavior. The coupling between spin and valley degrees of freedom is unambiguously demonstrated as the magnetic order is shown to be tunable with an in-plane magnetic field, or a perpendicular electric field. In addition, we examine the influence of SOC on the isospin order and stability of superconductivity. Our findings establish an efficient experimental knob to engineer topological properties of moire bands in twisted bilayer graphene and related systems.
Tailoring electron transfer dynamics across solid-liquid interfaces is fundamental to the interconversion of electrical and chemical energy. Stacking atomically thin layers with a very small azimuthal misorientation to produce moire superlattices ena
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