Gate‐Tunable Transport Properties of In Situ Capped Bi₂Te₃ Topological Insulator Thin Films

Abstract

Combining the ability to prepare high-quality, intrinsic Bi2Te3 topological insulator thin films of low carrier density with in-situ protective capping, we demonstrate a pronounced, gate-tunable change in transport properties of Bi2Te3 thin films. Using a back-gate, the carrier density is tuned by a factor of ∼ 7 in Al2O3 capped Bi2Te3 sample and by a factor of ∼ 2 in Te capped Bi2Te3 films. We achieve full depletion of bulk carriers, which allows us to access the topological transport regime dominated by surface state conduction. When the Fermi level is placed in the bulk band gap, we observe the presence of two coherent conduction channels associated with the two decoupled surfaces. Our magnetotransport results show that the combination of capping layers and electrostatic tuning of the Fermi level provide a technological platform to investigate the topological properties of surface states in transport experiments and pave the way towards the implementation of a variety of topological quantum devices. PACS numbers: 73.50.-h, 73.20.-r, 75.47.-m arXiv:1604.03722v1 [cond-mat.mes-hall]

Josephson Effect and Charge Distribution in Thin Bi2Te3 Topological Insulators

“…[27] Voltages V bg in the range of ±200 V are sufficient to create a triangular quantum well or to deplete carriers in the bottom region of the film. [28] I c is approximately constant. For positive gate voltage, it rises sharply at first, then grows with a smaller slope at high bias.…”

“…[ 27 ] Voltages V bg in the range of ±200 V are sufficient to create a triangular quantum well or to deplete carriers in the bottom region of the film. [ 28 ] Figures a and 2b depict the effect of charge (re‐)distribution in the material on the Josephson effect for two representative Josephson junctions that were patterned on films of 6 nm (JJ6/1) and 15 nm (JJ15/1), respectively. At 200 V gate bias, the Josephson coupling energy amounts to eI c R N ≈ 18 μeV for both devices.…”

Bulk contribution to magnetotransport properties of low-defect-density Bi2Te3 topological insulator thin films

“…In addition to employing in-situ characterization techniques as described in Refs. 12,13,33 , we used scanning transmission electron microscope (STEM) for a microstructural analysis of the samples presented in this study.…”

Bulk vs. Surface Structure of 3d Metal Impurities in Topological Insulator Bi2Te3

“…The Bi-chalcogenides such as Bi 2 Te 3 and Bi 2 Se 3 have long been known for their thermoelectric properties 1, 2 , but recently they have gained a great deal of attention as three-dimensional topological insulators with a large band gap and a single Dirac cone on the surface 3–8 . Additionally, the introduction of magnetic impurities into Bi-chalcogenides can break time-reversal symmetry and open an energy gap at the Dirac point of the surface states 9–11 .…”