Topological states and phase transitions in Sb2Te3-GeTe multilayers

Abstract

Topological insulators (TIs) are bulk insulators with exotic ‘topologically protected’ surface conducting modes. It has recently been pointed out that when stacked together, interactions between surface modes can induce diverse phases including the TI, Dirac semimetal, and Weyl semimetal. However, currently a full experimental understanding of the conditions under which topological modes interact is lacking. Here, working with multilayers of the TI Sb2Te3 and the band insulator GeTe, we provide experimental evidence of multiple topological modes in a single Sb2Te3-GeTe-Sb2Te3 structure. Furthermore, we show that reducing the thickness of the GeTe layer induces a phase transition from a Dirac-like phase to a gapped phase. By comparing different multilayer structures we demonstrate that this transition occurs due to the hybridisation of states associated with different TI films. Our results demonstrate that the Sb2Te3-GeTe system offers strong potential towards manipulating topological states as well as towards controlledly inducing various topological phases.

Manipulation of dangling bonds of interfacial states coupled in GeTe-rich GeTe/Sb2Te3 superlattices

“…As reported in many topological insulators or low dimensional systems with strong spin-orbit coupling 39 – 41 , both topological surface and bulk states can act as independent conducting channels and provide quantum correction Δσ in the equation 1 . Meanwhile, when surface states get coherent coupled through bulk states, α will be smaller than 0.5 N (N is the number of surfaces states) 20 , 21 , 39 , 44 . In an all, though we could not determine the number of the surface states quantitatively, we could figure out the surface state and their trend of coherent coupling qualitatively by the comparison of α value to 0.5.…”

“…In an all, though we could not determine the number of the surface states quantitatively, we could figure out the surface state and their trend of coherent coupling qualitatively by the comparison of α value to 0.5. It is commonly used in the exploration of topological insulators (TI) and exotic heterostructures 21 , 22 .…”

Intrinsic spin Hall conductivity in three-dimensional topological insulator/normal insulator heterostructures

“…Our treatment of the QSHE problem is distinct from most of the ones discussed previously [14,[26][27][28][30][31][32] since we incorporate the effect of the TI/NI interfaces and the edges of the TI film through the corresponding natural boundary conditions featured by the IP or EP [see Eqs. (5) and (29)], respectively. We demonstrate, by the example of the NI/TI/NI trilayer, that the interface and edge states and, as a consequence, the QSHE regime can be manipulated by changing the conditions at the TI film boundaries.…”

“…The solution of the boundary problem of Eqs. (4) and (5) answers the important question on how the IP located just at the boundaries affects the electron states inside the 3D TI film. Here we go beyond the open boundary condition, where the state has zero amplitude at the interfaces, (±l) = 0.…”

“…From the viewpoint of the application perspective of solid-state materials with unusual electron properties for spintronic devices, design and fabrication of semiconductor heterostructures comprising three-dimensional (3D) topological insulator (TI) thin films interfaced with normal insulator (NI) films is undoubtedly a promising way [1][2][3][4][5][6][7][8]. The specific character of the bulk electron structure of 3D TI gives rise to electron states appearing at the TI/NI interfaces, where the topological invariant changes.…”