Topological insulator homojunctions including magnetic layers: the example of n-p type ($n$-QLs Bi${}_2$Se${}_3$/Mn-Bi${}_2$Se${}_3$) heterostructures

Homojunctions between Bi${}_2$Se${}_3$ and its Mn-doped phase are investigated as a sample geometry to study the influence of spin degrees of freedom on topological insulator properties. $n$ quintuple layers (QLs) of Bi${}_2$Se${}_3$ are grown ontop of Mn-doped Bi${}_2$Se${}_3$ by molecular beam epitaxy for $0\le n \le 30,$QLs, allowing to unhamperedly monitor the development of electronic and topological properties by surface sensitive techniques like angle resolved photoemission spectroscopy. With increasing $n$, a Mn-induced gap at the Dirac point is gradually filled in an “hourglass” fashion to reestablish a topological surface state at $n\sim 9$QLs. Our results suggest a competition of upwards and downwards band bending effects due to the presence of an n-p type interface, which can be used to tailor topological and quantum well states independently.