Majorana bound states in encapsulated bilayer graphene

Abstract

The search for robust topological superconductivity and Majorana bound states continues, exploring both one-dimensional (1D) systems such as semiconducting nanowires and two-dimensional (2D) platforms. In this work we study a 2D approach based on graphene bilayers encapsulated in transition metal dichalcogenides that, unlike previous proposals involving the Quantum Hall regime in graphene, requires weaker magnetic fields and does not rely on interactions. The encapsulation induces strong spin-orbit coupling on the graphene bilayer, which opens a sizeable gap and stabilizes fragile pairs of helical edge states. We show that, when subject to an in-plane Zeeman field, armchair edges can be transformed into p-wave one-dimensional topological superconductors by contacting them laterally with conventional superconductors. We demonstrate the emergence of Majorana bound states (MBSs) at the sample corners of crystallographically perfect flakes, belonging either to the D or the BDI symmetry classes depending on parameters. We compute the phase diagram, the resilience of MBSs against imperfections, and their manifestation as a 4\piπ-periodic effect in Josephson junction geometries, all suggesting the existence of a topological phase within experimental reach.

Stabilizing the Inverted Phase of a WSe2/BLG/WSe2 Heterostructure via Hydrostatic Pressure

“…This gapped phase is distinct from the band insulating phase at large u in that the valence and conduction bands are no longer layer polarized, hence it is usually referred to as inverted phase (IP). It is worth mentioning that the IP at | u | < |λ I t | is weakly topological unlike the trivial band insulating phase. , …”

“…The IP has a distinct topology from the band insulator phase at large D , and the presence of edge states are expected . The presence of these states should be studied in better defined sample geometries , or using supercurrent interferometry. , Opposed to the weak protection of the edge states in this system, a strong topological insulator phase is predicted in ABC trilayer graphene. , Furthermore, pressure could also be used in case of magic-angle twisted BLG, in which topological phase transitions between different Chern insulator states are expected as a function of SOI strength …”

Supercurrent mediated by helical edge modes in bilayer graphene

“…We may improve the minimal model by adopting a more microscopic description with several trivial transport channels flowing along vacuum edges 39 , 40 , and two helical modes flowing all around the BLG junction, as expected from the band-inverted phase 19 , 28 , 44 . A coupling τ between vacuum and helical states enables an inter-edge scattering mechanism, see Fig.…”

“…The clear 2Φ 0 -periodic signature in our SQI experiment suggests an enticing prospect of detecting topological 4 π -periodic current-phase relations in this system 8 , which requires the investigation of the a.c. Josephson effect 17 , 18 , 45 and/or non-equilibrium effects at finite bias in a.c. supercurrent 46 . The observation of gate tunable helical edge-mediated supercurrents opens a promising new avenue 44 towards topological superconductivity and Majorana physics in van der Waals materials.…”

Moiré-enabled topological superconductivity in twisted bilayer graphene

“…This versatility increases considerably the range of phenomena that can be explored in van der Waals materials. In particular, the combination of Rashba SOC, Zeeman splitting and superconductivity in van der Waals heterostructures can give rise to topological superconductivity [14][15][16][17][18]. These ingredients, difficult to find in a single material, can be engineered in a van der Waals heterostructure through the appropriate combination of 2D materials.…”