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Register a new userDistortion and electric field control of band structure of silicene
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Authors
Gul Rahman
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Density functional theory with local density approximation for exchange and correlation functional is used to tune the electronic band structure of silicene monolayer. The cohesive energy of free standing monolayer is increasing (decreasing) with external electric field (distortion). Electrons in silicene behave like Dirac fermions, when the bond angle between the Si atoms is larger than $sim 102^{0}$. Large distortions destroy the electronic structure of silicene and silicene is no longer a semi-metallic material, and the distorted silicene acts like an $n$-doped system. Electric field opens a band gap around $K$ point in the Brillouin zone, which increases with electric field. The bond angle between the Si atoms is a key player to determine the presence or absence of Dirac cones in silicene.
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Polar textures have attracted significant attention in recent years as a promising analog to spin-based textures in ferromagnets. Here, using optical second harmonic generation based circular dichroism, we demonstrate deterministic and reversible control of chirality over mesoscale regions in ferroelectric vortices using an applied electric field. The microscopic origins of the chirality, the pathway during the switching, and the mechanism for electric-field control are described theoretically via phase-field modeling and second-principles simulations, and experimentally by examination of the microscopic response of the vortices under an applied field. The emergence of chirality from the combination of non-chiral materials and subsequent control of the handedness with an electric field has far-reaching implications for new electronics based on chirality as a field controllable order parameter.
We study the geometric and electronic structures of silicene monolayer using density functional theory based calculations. The electronic structures of silicene show that it is a semi-metal and the charge carriers in silicene behave like massless Dirac-Fermions since it possesses linear dispersion around Dirac point. Our results show that the band gap in silicene monolayer can be opened up at Fermi level due to an external electric field by breaking the inversion symmetry. The presence of buckling in geometric structure of silicene plays an important role in breaking the inversion symmetry. We also show that the band gap varies linearly with the strength of external electric field. Further, the value of band gap can be tuned over a wide range.
The impact of an applied electric field on the exchange coupling parameters has been investigated based on first-principles electronic structure calculations by means of the KKR Green function method. The calculations have been performed for a Fe film, free-standing and deposited on two different substrates, having 1 monolayer (ML) thickness to minimize the effect of screening of the electric field typical for metallic systems. By comparing the results for the free-standing Fe ML with those for Fe on the various substrates, we could analyze the origin of the field-induced change of the exchange interactions. Compared to the free-standing Fe ML, in particular rather pronounced changes have been found for the Fe/Pt(111) system due to the localized electronic states at the Fe/Pt interface, which are strongly affected by the electric field and which play an important role for the Fe-Fe exchange interactions.
We use the tight-binding model and the random-phase approximation to investigate the intrinsic plasmon in silicene. At finite temperatures, an undamped plasmon is generated from the interplay between the intraband and the interband-gap transitions. The extent of the plasmon existence range in terms of momentum and temperature, which is dependent on the size of single-particle-excitation gap, is further tuned by applying a perpendicular electric field. The plasmon becomes damped in the interband-excitation region. A low damped zone is created by the field-induced spin split. The field-dependent plasmon spectrum shows a strong tunability in plasmon intensity and spectral bandwidth. This could make silicene a very suitable candidate for plasmonic applications.
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