Surface State Dynamics of Topological Insulators Investigated by Femtosecond Time- and Angle-Resolved Photoemission Spectroscopy

Hamoon Hedayat,Hemian Yi,Claudia Dallera,Giulio Cerullo,Xingjiang Zhou,Chaoyu Chen,Ettore Carpene,Davide Bugini

doi:10.3390/app8050694

Hamoon Hedayat, Hemian Yi + Show 6 more

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https://doi.org/10.3390/app8050694

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Abstract

Topological insulators (TI) are known for striking quantum phenomena associated with their spin-polarized topological surface state (TSS). The latter in particular forms a Dirac cone that bridges the energy gap between valence and conduction bands, providing a unique opportunity for prospective device applications. In TI of the BixSb2−xTeySe3−y (BSTS) family, stoichiometry determines the morphology and position of the Dirac cone with respect to the Fermi level. In order to engineer specific transport properties, a careful tuning of the TSS is highly desired. Therefore, we have systematically explored BSTS samples with different stoichiometries by time- and angle-resolved photoemission spectroscopy (TARPES). This technique provides snapshots of the electronic structure and discloses the carrier dynamics in surface and bulk states, providing crucial information for the design of electro-spin current devices. Our results reveal the central role of doping level on the Dirac cone structure and its femtosecond dynamics. In particular, an extraordinarily long TSS lifetime is observed when the the vertex of the Dirac cone lies at the Fermi level.

Highlights

Due to their unconventional electronic structure, topological insulators (TI) are potential candidates for next-generation electronic and spintronic devices [1,2,3]
Electrons are optically transferred above the Fermi energy (FE), filling the topological surface state (TSS)
We have studied the electronic dynamics of the TSS in the Bix Sb2− x Tey Se3−y (BSTS) family of compounds with different doping levels

Summary

Introduction

Due to their unconventional electronic structure, topological insulators (TI) are potential candidates for next-generation electronic and spintronic devices [1,2,3]. They behave like standard insulators or semiconductors in the bulk, but stimulating physics takes place at their surface. Recent studies have shown several unique features of TI, including observations of the quantum spin Hall effect [4], Majorana fermions [5], the topological magnetoelectric effect [6], magnetic monopoles [7], nonlinear modulation of the electromagnetic field [8], and the anomalous quantum Hall effect [9]. The major obstacle is the large contribution of bulk electrons that hamper surface transport properties [10]. Focusing on the Bix Sb2− x Tey Se3−y (BSTS) family, some of the most promising ternary and quaternary compounds were identified as

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