Weak antilocalization in topological crystalline insulator SnTe films deposited using amorphous seeding on SrTiO3

Stephen D Albright,Frederick J Walker,Charles H Ahn,Ke Zou

doi:10.1063/5.0065627

Stephen D Albright, Frederick J Walker + Show 2 more

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https://doi.org/10.1063/5.0065627

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Abstract

Topological crystalline insulators (TCIs) promise spin-polarized or dissipationless transport, which can be controlled by crystal symmetry breaking through applied strain or electric field. To realize TCI devices with gate-controlled topological states, it is necessary to develop methods for depositing continuous and thin TCI films on substrates suitable for electric-field gating. Here, we present an optimized templating procedure for depositing single-orientation, continuous films of TCI SnTe on SrTiO3, which is an oxide with a wide bandgap and large dielectric constant suitable for gated devices. This process takes advantage of a thin SnTe template layer crystallized after amorphous deposition, with additional SnTe being grown by molecular beam epitaxy and monitored with in situ laser ellipsometry. Continuous, single-phase SnTe films with a (001) orientation relative to the SrTiO3 lattice are achieved. Magnetoconductivity measurements of SnTe films reveal a coexistence of weak antilocalization, consistent with topologically non-trivial states, and weak localization, consistent with trivial states from the bulk. This method of analysis may be suitable to analyze the magnetotransport characteristics of any topological material with carriers in both topological and trivial bulk states. The maximum phase coherence length is achieved for films thicker than 20 unit cells, which could be used for gated-SnTe devices.

Highlights

With its high dielectric constant and large bandgap, SrTiO3 is a promising substrate for gated-SnTe, with SrTiO3 serving as an insulating buffer layer between SnTe and a conducting oxide gate
We implement a thin templating SnTe layer that is crystallized after amorphous deposition, followed by molecular beam epitaxy growth monitored with high resolution laser ellipsometry to control both deposition and evaporation of the SnTe film
The origins of this deviation may be the coexistence of topologically trivial states from the SnTe bulk, which could give the opposite effect, weak localization (WL), with the non-trivial states expected at the SnTe surfaces

Summary

INTRODUCTION

Topological crystalline insulators (TCIs) are a subclass of topological materials that possess conducting surface and edge states due to band inversion at locations of high crystal symmetry in the Brillouin zone. The prototypical TCI, SnTe (and its family of Pb-alloyed rocksalt compounds), has been thoroughly studied because the crystal symmetry protection of TCIs offers new methods for control of its topological states. Contrasting with conventional TIs, applying strain or an electric field can break the crystal symmetry, gapping the topological states. A topological transistor based on this principle using gated SnTe has been proposed, with an applied electric field breaking the SnTe crystalline symmetry.. Contrasting with conventional TIs, applying strain or an electric field can break the crystal symmetry, gapping the topological states.. A topological transistor based on this principle using gated SnTe has been proposed, with an applied electric field breaking the SnTe crystalline symmetry.. A modified molecular beam epitaxy technique called co-sublimation-deposition (coSubDep) has been shown to produce SnTe films as thin as 10 u.c. on SrTiO3 with higher continuity and crystalline uniformity.. We implement a thin templating SnTe layer that is crystallized after amorphous deposition, followed by molecular beam epitaxy growth monitored with high resolution laser ellipsometry to control both deposition and evaporation of the SnTe film. The thin template layer results in high quality, continuous SnTe films with markedly higher inplane crystalline uniformity than previously achieved. We perform magnetoconductivity measurements to characterize the topological states of uniform SnTe thin films, to quantify the number of independent topological channels present and the inelastic mean free path of topological carriers as a function of film thickness

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SUMMARY