Browsing by Author "Edmonds, MT"

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    Antiferromagnetic topological insulating state in Tb0.02Bi1.08Sb0.9Te2S single crystals
    (American Physical Society (APS), 2023-03-13) Guo, L; Zhao, WY; Li, Q; Xu, M; Chen, L; Bake, A; Vu, THY; He, YH; Fang, Y; Cortie, DL; Mo, SK; Edmonds, MT; Wang, XL; Dong, S; Karel, J; Zheng, RK
    Topological insulators are emerging materials with insulating bulk and symmetry protected nontrivial surface states. One of the most fascinating transport behaviors in a topological insulator is the quantized anomalous Hall insulator, which has been observed in magnetic-topological-insulator-based devices. In this work, we report a successful doping of rare earth element Tb into Bi1.08Sb0.9Te2S topological insulator single crystals, in which the Tb moments are antiferromagnetically ordered below ∼10 K. Benefiting from the in-bulk-gap Fermi level, transport behavior dominant by the topological surface states is observed below ∼150 K. At low temperatures, strong Shubnikov-de Haas oscillations are observed, which exhibit 2D-like behavior. The topological insulator with long range magnetic ordering in rare earth doped Bi1.08Sb0.9Te2S single crystal provides an ideal platform for quantum transport studies and potential applications. ©2023 American Physical Society.
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    Increased phase coherence length in a porous topological insulator
    (American Physical Society (APS), 2023-06-15) Nguyen, A; Akhgar, G; Cortie, DL; Bake, A; Pastuovic, Z; Zhao, W; Liu, C; Chen, YH; Suzuki, K; Fuhrer, MS; Culcer, D; Hamilton, AR; Edmonds, MT; Karel, J
    The surface area of Bi2Te3 thin films was increased by introducing nanoscale porosity. Temperature dependent resistivity and magnetotransport measurements were conducted both on as-grown and porous samples (23 and 70 nm). The longitudinal resistivity of the porous samples became more metallic, indicating the increased surface area resulted in transport that was more surfacelike. Weak antilocalization was present in all samples, and remarkably the phase coherence length doubled in the porous samples. This increase is likely due to the large Fermi velocity of the Dirac surface states. Our results show that the introduction of nanoporosity does not destroy the topological surface states but rather enhances them, making these nanostructured materials promising for low energy electronics, spintronics and thermoelectrics. ©2023 American Physical Society
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    Large magnetic gap in a designer ferromagnet–topological insulator–ferromagnet heterostructure
    (Wiley, 2022-03-08) Li, Q; Trang, CX; Wu, WK; Hwang, JW; Cortie, DL; Medhekar, N; Mo, SK; Yang, SA; Edmonds, MT
    Combining magnetism and nontrivial band topology gives rise to quantum anomalous Hall (QAH) insulators and exotic quantum phases such as the QAH effect where current flows without dissipation along quantized edge states. Inducing magnetic order in topological insulators via proximity to a magnetic material offers a promising pathway toward achieving the QAH effect at a high temperature for lossless transport applications. One promising architecture involves a sandwich structure comprising two single-septuple layers (1SL) of MnBi2Te4 (a 2D ferromagnetic insulator) with ultrathin few quintuple layer (QL) Bi2Te3 in the middle, and it is predicted to yield a robust QAH insulator phase with a large bandgap greater than 50 meV. Here, the growth of a 1SL MnBi2Te4/4QL Bi2Te3/1SL MnBi2Te4 heterostructure via molecular beam epitaxy is demonstrated and the electronic structure probed using angle-resolved photoelectron spectroscopy. Strong hexagonally warped massive Dirac fermions and a bandgap of 75 ± 15 meV are observed. The magnetic origin of the gap is confirmed by the observation of the exchange-Rashba effect, as well as the vanishing bandgap above the Curie temperature, in agreement with density functional theory calculations. These findings provide insights into magnetic proximity effects in topological insulators and reveal a promising platform for realizing the QAH effect at elevated temperatures. © 2022 The Authors
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    Transport measurements in porous Bi2Te3 thin films
    (American Physical Society, 2022-03-16) Akhgar, G; Nguyen, A; Cortie, DL; Bake, A; Zhao, WY; Liu, C; Fuhrer, MS; Culcer, D; Hamilton, AR; Edmonds, MT; Karel, J
    Recent theoretical work has predicted the existence of disordered topological insulators , however, minimal experimental work has been conducted on disordered TIs. Here we used molecular-beam epitaxy (MBE) to grow Bi2Te3 thin films that were comprised of nanocrystals embedded in an amorphous matrix. Further disorder was introduced through Ne ion irradiation which produced porosity in the films. In this talk we will present magnetoresistance measurements on porous Bi2Te3, where weak anti-localisation (WAL) was observed. The magnetoresistance curves were fitted using a Dirac Fermion model specifically derived to model weak antilocalization in TIs. Our results also show that the temperature dependence of the phase coherence length in porous Bi2Te3, with an increased surface to volume ratio, exhibits 2D-like transport.