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.
Highlights
topological surface modes (TSMs) in structures of the type we report
The strong spin-orbit interaction in Topological insulators (TIs) engenders positive quantum corrections to σin the form of weak antilocalization (WAL) at low T18 which manifests as a characteristic cusp in the magnetoresistance described by the Hikami-Larkin-Nagaoka (HLN) equation[18]:
Σxx indicates the longitudinal component of conductivity and the superscript 2D indicates that the equation is valid for a two-dimensional conducting sheet, B⊥ is the magnetic field perpendicular to the 2D plane, αis a parameter = 0.5 for each 2D WAL channel, e is the electronic charge, is Planck’s constant divided by 2π,φ is the phase coherence length, and Ψis the digamma function
Summary
Topological insulators (TIs) are a recently emerged class of materials which are insulating in the bulk, but whose surface harbours ‘topologically protected’ conducting modes[1]. There have been reports of TIs in superlattice structures including PbSe-Bi2Se3 structures[7,8], Bi14Rh3I99, and Sb-Te binary systems[10,11], the crucial aspect of how the TSMs couple across the intervening layers remains unexplored. In this manuscript we investigate the low-temperature (low-T) electrical properties of molecular beam epitaxy (MBE)-grown bi-layer and tri-layer structures of Sb2Te3, a well-known TI12, and GeTe, a narrow band gap semiconductor that goes superconducting at very low T13,14. Our approach of utilising MBE-grown multilayers is promising in that it potentially overcomes both these limitations
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