We report peculiar charge and spin transport properties in S-shaped silicene junctions with the Kane-Mele tight-binding model. In this work, we investigate the effects of electric and exchange fields on the charge and spin transport properties. Our results show that by applying a perpendicular electric field, metal-semiconductor and also semimetal-semiconductor phase transitions occur in our systems. Furthermore, full spin current can be obtained in the structures, so the half-metallic states are observable. Our results enable us to control charge and spin currents and provide new opportunities and applications in silicene-based electronics, optoelectronics, and spintronics.

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The shortcomings of mono-component systems, e.g., the gapless nature of graphene, the lack of air-stability in phosphorene, etc. have drawn great attention toward stacked materials expected to show interesting electronic and optical properties. Using the tight-binding approach and the Green's function method, we investigate the electronic properties of armchair-edged lateral phosphorene/graphene heterostructures, which are either semiconductor/semiconductor or semiconductor/metal heterostructures, depending on the width of graphene ribbon. It is found that the system is narrow-gapped, and the bandgap can be modulated by tuning the size of the domains. Besides, the analysis of the bandgap variation against the width of the component phosphorene ribbon indicates that, in semiconductor/metal heterostructure, phosphorene ribbon does not induce any electronic state near the Fermi level, suggesting that the suppressed electron transport should be attributed to the hole transfer across the interface. Furthermore, we show that the transverse electric field can significantly diversify the electronic behavior of the heterostructure, i.e., the heterostructure undergoes the semiconductor-metal phase transition. Moreover, tuning the transverse electric field yields an intriguing possibility that the system can undergo a topological phase transition from a band insulator to a topological insulator.

We study the topological properties of finite-size S-shaped graphene junctions with distinctive edge features subjected to the perpendicular magnetic field, using the tight-binding model. The quantum confinement and edge effects induced by the specific junction give rise to significant modifications in the Hofstadter spectra of the bent flakes, when compared to those of their perfect forms. Moreover, the results show that in absence of a magnetic field, the sharpest zigzag-edged corners support the edge states rather than the others, but the magnetic field leads to the localization of the edge states along the whole perimeter of the flakes. Furthermore, based on the Green's function method, we investigate the electron transport through our proposed junctions. We show that, under magnetic flux, one can effectively control the energy gap and the conductance around the Fermi energy. Moreover, the transitions between metallic, semimetallic, and semiconducting phases are possible by the magnetic flux in the S-shaped junctions.