Customizing topological phases in the twisted bilayer superconductors with even-parity pairings

We investigate the topological properties of twisted bilayer superconductors with different even-parity pairings in each layer.In the presence of spin-orbit coupling,the Hamiltonian is mapped into an effective odd-parity superconductor.Based on this,we deduce the topological properties by examining the relative configuration between Fermi surface and Dirac pairing node.We show that mixed Rashba and Dresselhaus spin-orbit coupling and anisotropic hopping terms,which break the C_(4)symmetry of the Fermi surface,can induce first-order topological superconductors with non-zero bulk Chern number.This provides a versatile way to control the topological phases of bilayer superconductors by adjusting the twisted angle and chemical potential.We demonstrate our results using a typical twisted angle of 53.13°,at which the translation symmetry is restored and the Chern number and edge state are calculated using the Moir′e momentum.

Flattening is flattering: The revolutionizing 2D electronic systems

Two-dimensional (2D) crystals are known to have no bulk but only surfaces and edges, thus leading to unprecedented properties thanks to the quantum confinements. For half a century, the compression of z-dimension has been attempted through ultra-thin films by such as molecular beam epitaxy. However, the revisiting of thin films becomes popular again, in another fashion of the isolation of freestanding 2D layers out of van der Waals (vdW) bulk compounds. To date, nearly two decades after the nativity of the great graphene venture, researchers are still fascinated about flattening, into the atomic limit, all kinds of crystals, whether or not they are vdW. In this introductive review, we will summarize some recent experimental progresses on 2D electronic systems, and briefly discuss their revolutionizing capabilities for the implementation of future nanostructures and nanoelectronics.

Formation of topological domain walls and quantum transport properties of zero-line modes in commensurate bilayer graphene systems

We study theoretically the construction of topological conducting domain walls with a finite width between AB/BA stacking regions via finite element method in bilayer graphene systems with tunable commensurate twisting angles.We find that the smaller is the twisting angle,the more significant the lattice reconstruction would be,so that sharper domain boundaries declare their existence.We subsequently study the quantum transport properties of topological zero-line modes which can exist because of the said domain boundaries via Green’s function method and Landauer–Büttiker formalism,and find that in scattering regions with triintersectional conducting channels,topological zero-line modes both exhibit robust behavior exemplified as the saturated total transmission Gtot≈2e_(2)/h and obey a specific pseudospin-conserving current partition law among the branch transport channels.The former property is unaffected by Aharonov–Bohm effect due to a weak perpendicular magnetic field,but the latter is not.Results from our genuine bilayer hexagonal system suggest a twisting angle aroundθ≈0.1°for those properties to be expected,consistent with the existing experimental reports.