Photo-Induced Topological Phase Transition and a Single Dirac-Cone State in Silicene

Abstract

Silicene (a monolayer of silicon atoms) is a quantum spin Hall insulator (QSHI), which undergoes a topological phase transition to a band insulator under external electric field $E_z$. We investigate a photo-induced topological phase transition by irradiating circular polarized light at fixed $E_z$. The band structure and also the topological property are modified by photon dressing. By increasing the intensity of light at $E_z=0$, a photo-induced quantum Hall insulator (P-QHI) is realized, where the quantum Hall effect occurs without magnetic field. Its edge modes are anisotropic chiral, in which the velocities of up and down spins are different. There appears a spin polarized metal characterized by topological flat bands at the critical point between the QSHI and P-QHI. At $E_z>E_{\text{cr}}$ with a certain critical field $E_{\text{cr}}$, a photo-induced spin-polarized quantum Hall insulator emerge. This is a new state of matter, possessing one Chern number and one half spin-Chern numbers. The edge mode supports a perfectly spin-polarized current, which are different from the chiral or helical edge modes. We newly discovered a single Dirac-cone state along a phase boundary. A distinctive hallmark of the state is that one of the two Dirac valleys is closed with a linear dispersion and the other open with a parabolic dispersion.

4 pages, 4 figures. arXiv admin note: text overlap with arXiv:1206.5378

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Cited by in corpus (3)

• Spin-Valleytronics in Silicene: Quantum-Spin-Quantum-Anomalous Hall Insulators and Single-Valley Semimetals
• Quantum criticality at the Chern-to-normal insulator transition
• Hexagonally Warped Dirac Cones and Topological Phase Transition in Silicene Superstructure