Topological Insulators in Twisted Transition Metal Dichalcogenide Homobilayers

Abstract

We show that moiré bands of twisted homobilayers can be topologically nontrivial, and illustrate the tendency by studying valence band states in ±K valleys of twisted bilayer transition metal dichalcogenides, in particular, bilayer MoTe2. Because of the large spin-orbit splitting at the monolayer valence band maxima, the low energy valence states of the twisted bilayer MoTe2 at +K (−K) valley can be described using a two-band model with a layer-pseudospin magnetic field ∆(r) that has the moiré period. We show that ∆(r) has a topologically non-trivial skyrmion lattice texture in real space, and that the topmost moiré valence bands provide a realization of the Kane-Mele quantum spin-Hall model, i.e., the two-dimensional time-reversal-invariant topological insulator. Because the bands narrow at small twist angles, a rich set of broken symmetry insulating states can occur at integer numbers of electrons per moiré cell. arXiv:1807.03311v2 [cond-mat.mes-hall]

Giant magnetic field from moiré induced Berry phase in homobilayer semiconductors

“…Remarkably, while the twisting moiré and biaxial moiré have identical pseudospin textures and magnetic field distribution, the uniaxial moiré is of a distinct texture that leads to an opposite magnetic field distribution. The magnetic flux per supercell ∫ • is a quantized value: 2 for twisting moiré and biaxial moiré and −2 for uniaxial moiré, corresponding to the fact that the pseudospin texture is of a skyrmion (19) and anti-skyrmion configuration respectively. Thus, the three different origins give rise to two topologically distinct types of moiré patterns.…”

Flat Chern Band from Twisted Bilayer MnBi2Te4

“…A prime example is twisted bilayer graphene (tBLG) [32][33][34][35], where the lowest two bands carry a fragile topology [36][37][38][39][40] and become flat near the magic twist angle θ ≈ 1.1 • . In addition, flat valley Chern bands can be realized in tBLG with aligned hBN substrate [41][42][43], twisted double bilayer graphene [44][45][46], ABC trilayer graphene on hBN [47][48][49] and twisted bilayer transition metal dichalcogenides [50,51], etc. The small bandwidths make electron-electron interactions important [52][53][54][55][56][57][58][59], and further lead to intriguing interacting phases in experiments including superconductivity, correlated insulator and QAH effect.So far, all of the experimental Moiré systems are timereversal (TR) invariant at the single particle level, thus the total Chern number always equals to zero.…”

Functional Mid‐Infrared Polaritonics in van der Waals Crystals

“…As researchers continue to create material systems with novel physics, and rich phase transitions, it is likely that new polaritonic properties will become observable. As discussed before, twisted bilayer graphene is one exciting candidate material to observe such effects, but twisted transition metal dichalcogenide (TMD) layers can also show novel effects such as interlayer excitonic states that are confined within a tunable moire potential and emergent topological states . Moreover, high‐quality graphene and bilayer graphene have recently been shown to display hydrodynamic properties and liquid nitrogen temperatures, which could affect plasmonic behavior .…”