Engineering multiple topological phases in nanoscale Van der Waals heterostructures: realisation of α-antimonene

Abstract

Van der Waals heterostructures have recently been identified as providing many opportunities to create new two-dimensional materials, and in particular to produce materials with topologicallyinteresting states. Here we show that it is possible to create such heterostructures with multiple topological phases in a single nanoscale island. We discuss their growth within the framework of diffusion-limited aggregation, the formation of moiré patterns due to the differing crystallographies of the materials comprising the heterostructure, and the potential to engineer both the electronic structure as well as local variations of topological order. In particular we show that it is possible to build islands which include both the hexagonal β-and rectangular α-forms of antimonene, on top of the topological insulator α-bismuthene. This is the first experimental realisation of α-antimonene, and we show that it is a topologically non-trivial material in the quantum spin Hall class.

Moiré patterns in van der Waals heterostructures

“…More rarely, the interfering crystalline structures (under-and overlayer) possess a rectangular symmetry, e.g., Bi on GaAs(110) [40], NaCl on Ag(100) [41], twisted bilayer phosphorene [42], or monolayer Bi (MBi) on α-Bi [43]. Our reports on group-V compounds on HOPG and MoS 2 [44,45] constitute, to the best of our knowledge, the only experimental reports focusing on the MPs generated by a mixed symmetry stacking (e.g., rectangular and hexagonal symmetries). The analysis of MPs in these mixed symmetry systems is particularly challenging.…”

“…Because of the strong spin-orbit coupling in Bi, many of its known allotropes are topologically nontrivial: α-Bi [49,50], β-Bi [51], and even bulk Bi [52] have all been reported to possess nontrivial topology, and most recently exotic hinge states have been reported in Bi nanowires [53]. An area of active investigation is whether the topological properties survive in the low-dimensional forms of these materials [45,50]. In fact the 2D forms of these materials are interesting because of the crystalline symmetries that are adopted.…”

“…α-Bismuthene (α-Bi) has been extensively investigated [44,[54][55][56][57][58][59][60][61][62][63] and is of particular relevance to the present work because Sb allotropes are grown on top of islands of α-Bi. The low-dimensional phases of antimonene (Sb) have been much less investigated: first-principles calculations were reported several years ago [64][65][66], but experimental realizations of β-Sb [67][68][69][70] and α-Sb [45,70,71] were only reported more recently. Topologically protected edge states are predicted for α-Sb [45], multilayer β-Sb [72,73], and sufficiently strained monolayer β-Sb [74].…”

Van der Waals Heteroepitaxial Growth of Monolayer Sb in a Puckered Honeycomb Structure

“…It is believed that BP‐structured monolayer (α‐allotrope) can be formed in other group V elements, such as Bi (bismuthene), Sb (antimonene), or As (arsenene), and many theoretical efforts have been made to predict their structures and properties . Comparing to their β‐allotrope of hexagonal honeycomb structure that has been widely studied experimentally, it still remains challenging to fabricate the large‐scale and high‐quality monolayer α‐allotrope of these group V monoelements, even though small patches of the α‐allotrope has been observed in some mixed structures …”

2D Elemental Nanomaterials Beyond Graphene

“…Mixed islands of α‐ and β‐antimonene have been obtained on a α ‐bismuthene substrate . Large‐scale synthesis of high‐quality α‐antimonene is essential for practical applications.…”