Topological multiferroic order in twisted transition metal dichalcogenide bilayers

Abstract

Layered van der Waals materials have risen as powerful platforms to artificially engineer correlated states of matter. Here we show the emergence of a multiferroic order in a twisted dichalcogenide bilayer superlattice at quarter-filling. We show that the competition between Coulomb interactions leads to the simultaneous emergence of ferrimagnetic and ferroelectric orders. We derive the magnetoelectric coupling for this system, which leads to a direct strong coupling between the charge and spin orders. We show that, due to intrinsic spin-orbit coupling effects, the electronic structure shows a non-zero Chern number, thus displaying a topological multiferroic order. We show that this topological state gives rise to interface modes at the different magnetic and ferroelectric domains of the multiferroic. We demonstrate that these topological modes can be tuned with external electric fields as well as triggered by supermoiré effects generated by a substrate. Our results put forward twisted van der Waals materials as a potential platform to explore multiferroic symmetry breaking orders and, ultimately, controllable topological excitations in magnetoelectric domains.

Moiré photonics and optoelectronics

“…Triggered by the discovery of correlated insulating states and unconventional superconductivity in magic-angle twisted bilayer graphene (TBG) (17,18), a plethora of exciting electronic, optical, and optoelectronic properties have been discovered in moiré superlattices (Fig. 1C), including moiré excitons (19)(20)(21)(22), versatile quantum light sources (23), orbital ferromagnetism (24)(25)(26), Wigner crystal states (11,27,28), stripe phases (29,30), topological multiferroic order (31), boson exciton crystals (32), and intelligent infrared sensing (33).…”

Stacking Order Engineering of Two-Dimensional Materials and Device Applications

“…Moiré superlattices of layered materials are emerging platforms for various types of topological effects and unravel rich interplay physics between topology and electron correlation, − resulting from their highly tunable flat electronic bands, lattice geometry, and correlation effects. For instance, recently in samples of Bernal stacked-bilayer graphene/h-BN superlattices, the fractional Chern insulators have been seen in a very large magnetic field (30 T) .…”

Atomic‐Scale Visualization of Multiferroicity in Monolayer NiI2

“…[14][15][16][17][18][19][20][21][22] These can be stacked and twisted in heterostructures, leading to a wide range of emergent phenomena including multiferroicity. [23][24][25][26][27][28] Recently, it was suggested that the multiferroicity of the bulk van der Waals compound NiI 2 remains in the mechanically-exfoliated few-layer [29] and monolayer limits. [30] Theoretical analyses have addressed the origin of this type-II multiferroic order to the combination of the magnetic spin-spiral order of NiI 2 and the strong spin-orbit (SOC) coupling of the I atoms.…”