Topological phase transition and electrically tunable diamagnetism in silicene

Abstract

Silicene is a monolayer of silicon atoms forming a honeycomb lattice. The lattice is actually made of two sublattices with a tiny separation. Silicene is a topological insulator, which is characterized by a full insulating gap in the bulk and helical gapless edges. It undergoes a phase transition from a topological insulator to a band insulator by applying external electric field. Analyzing the spin Chern number based on the effective Dirac theory, we find their origin to be a pseudospin meron in the momentum space. The peudospin degree of freedom arises from the two-sublattice structure. Our analysis makes clear the mechanism how a phase transition occurs from a topological insulator to a band insulator under increasing electric field. We propose a method to determine the critical electric field with the aid of diamagnetism of silicene. Diamagnetism is tunable by the external electric field, and exhibits a singular behaviour at the critical electric field. Our result is important also from the viewpoint of cross correlation between electric field and magnetism. Our finding will be important for future electro-magnetic correlated devices.

Emergence of Dirac and quantum spin Hall states in fluorinated monolayer As and AsSb

“…We notice that this splitting is not large enough to close the band gap, which implies that the system is a trivial semiconductor. Since the spin-up and -down bands are decoupled, the Z 2 index is identical to the spin Chern number C s modulo 2 [34]. From H eff τ , the spin Chern number can be calculated to be [1 − sgn( − λ 1 +λ 2 2 )]/2, which is 1 and 0 for fluorinated ML As and AsSb, respectively.…”

Is silicene the next graphene?

“…40 While still small, it is sufficient to help demonstrate the quantum spin Hall effect; this effect arises from the existence of a bulk gapped state and gapless conducting edge states at the boundaries, an example of a topological insulator. An interesting proposal is to control the bandgap using an external electric field, [41][42][43] transforming silicene from a topological insulator into a band insulator. Indeed, silicene has been predicted to have an extremely rich phase diagram of topological states with unique quantum states of matter such as a hybrid quantum Hall-quantum anomalous Hall state (the anomalous effect being the well-known quantum Hall effect in the absence of an external magnetic field) and a so-called valley-polarized metal (resulting from electron transfer from a conduction valley to a different hole valley), leading to the new field of spin valleytronics.…”

Thermal conductance by Dirac fermions in a normal-insulator-superconductor junction of silicene

“…Such tunability opens up the possibility to undergo a topological phase transition from topologically non-trivial state to a trivial state depending on whether the applied electric field is less or more than the critical value at which the band gap closes. Thus a rich varity of topological phases can be realised in silicene 18,[27][28][29][30] under suitable circumstances.…”