Disorder effects in topological insulator thin films

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Abstract

Thin films of topological insulators (TI) attract large attention because of expected topological effects from the intersurface hybridization of Dirac points. However, these effects may be depleted by unexpectedly large energy smearing Γ of surface Dirac points by the random potential of abundant Coulomb impurities. We show that in a typical TI film with large dielectric constant ∼50 sandwiched between two low dielectric-constant layers, the Rytova-Chaplik-Entin-Keldysh modification of the Coulomb potential of a charge impurity allows a larger number of the film impurities to contribute to Γ. As a result, Γ is large and independent of the TI film thickness d for d>5 nm. In thinner films Γ grows with decreasing d due to reduction of screening by the hybridization gap. We study the surface conductivity away from the neutrality point and at the neutrality point. In the latter case, we find the maximum TI film thickness at which the hybridization gap is still able to make a TI film insulating and allow observation of the quantum spin Hall effect, dmax∼7 nm.

Original languageEnglish (US)
Article number165409
JournalPhysical Review B
Volume103
Issue number16
DOIs
StatePublished - Apr 12 2021

Bibliographical note

Funding Information:
We are grateful to S.K. Chong, V.V. Deshpande, B. Skinner, and D. Weiss and for useful discussions. Y.H. was partially supported by the William I. Fine Theoretical Physics Institute.

Publisher Copyright:
© 2021 American Physical Society.

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