Abstract
Bilayer phosphorene attracted considerable interest, giving a potential application in nanoelectronics owing to its natural bandgap and high carrier mobility. However, very little is known regarding the possible usefulness in spintronics as a quantum spin Hall (QSH) state of material characterized by a bulk energy gap and gapless spin-filtered edge states. Here, we report a strain-induced topological phase transition from normal to QSH state in bilayer phosphorene, accompanied by band-inversion that changes number from 0 to 1, which is highly dependent on interlayer stacking. When the bottom layer is shifted by 1/2 unit-cell along zigzag/armchair direction with respect to the top layer, the maximum topological bandgap 92.5 meV is sufficiently large to realize QSH effect even at room-temperature. An optical measurement of QSH effect is therefore suggested in view of the wide optical absorption spectrum extending to far infra-red, making bilayer phosphorene a promising candidate for opto-spintronic devices.
Highlights
Quantum spin Hall state of matter has a charge excitation energy gap in the bulk and gapless spin-filtered edge-states on the boundary with a Dirac-cone-like linear energy dispersion[27,28,29,30,31,32,33,34,35,36,37]
When the bottom layer is shifted by 1/2 unit cell along the zigzag or the armchair direction with respect to the top layer, the maximum topological bandgap can reach up to 92.5 meV, which is sufficiently large to realize the quantum spin Hall effect even at room temperature
The optical property of bilayer phosphorene is examined based on a real-space and real-time time-dependent density functional theory, which shows that the optical absorption spectrum of bilayer phosphorene becomes wide and is even extended to far-infra-red region in quantum spin Hall (QSH) state
Summary
Quantum spin Hall state of matter has a charge excitation energy gap in the bulk and gapless spin-filtered edge-states on the boundary with a Dirac-cone-like linear energy dispersion[27,28,29,30,31,32,33,34,35,36,37]. The special edge-states, which are topologically protected by the time reversal symmetry, can survive the nonmagnetic scattering and geometry perturbations, open new ways for backscattering-free transport Such systems have stimulated enormous research activities in condensed matter physics due to their novel quantum spin Hall effect and the potential application in quantum computation and spintronics[29,30]. The optical property of bilayer phosphorene is examined based on a real-space and real-time time-dependent density functional theory, which shows that the optical absorption spectrum of bilayer phosphorene becomes wide and is even extended to far-infra-red region in QSH state Such improvement in optical response is indispensable for the broadband photodetection. An optical experimental setup is improved to measure the QSH effect in bilayer phosphorene
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