. (2015) Robust local and nonlocal transport in the topological Kondo insulator SmB6in the presence of a high magnetic field. Physical Review B, 92 (8). 085103. Permanent WRAP URL:http://wrap.warwick.ac.uk/87833 Copyright and reuse:The Warwick Research Archive Portal (WRAP) makes this work by researchers of the University of Warwick available open access under the following conditions. Copyright © and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable the material made available in WRAP has been checked for eligibility before being made available.Copies of full items can be used for personal research or study, educational, or not-for-profit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. Publisher statement: © 2015 American Physical Society A note on versions:The version presented here may differ from the published version or, version of record, if you wish to cite this item you are advised to consult the publisher's version. Please see the 'permanent WRAP URL' above for details on accessing the published version and note that access may require a subscription.For more information, please contact the WRAP Team at: wrap@warwick.ac.uk Robust local and non-local transport in the Topological Kondo Insulator SmB 6 in the presence of high magnetic field SmB6 has been predicted to be a Kondo Topological Insulator with topologically protected conducting surface states. We have studied quantitatively the electrical transport through surface states in high quality single crystals of SmB6. We observe a large non-local surface signal at temperatures lower than the bulk Kondo gap scale. Measurements and finite element simulations allow us to distinguish unambiguously between the contributions from different transport channels. In contrast to general expectations, the electrical transport properties of the surface channels was found to be insensitive to high magnetic fields. Local and non-local magnetoresistance measurements allowed us to identify definite signatures of helical spin states and strong inter-band scattering at the surface.
Despite several years of studies, the origin of slow-kinetics of charge-carriers at the surface-states of strong topological insulators remains abstruse. In this article, we report on studies of charge dynamics of thin films of the 3-dimensional strong topological insulator material BiSbTeSe1.6 grown by pulsed laser deposition (PLD). The bulk of the films was insulating, making them suitable for transport studies of topological surface-states. Despite being disordered and granular, the films show definite signatures of the presence of topological surface-states with electronic transport coherence lengths comparable to those of high-quality grown films grown by molecular beam epitaxy (MBE). At high temperatures, the resistance fluctuations in these films were found to be dominated by trapping-detrapping of charge carriers from multiple defect-levels of the bulk. At low temperatures, fluctuations in the resistance of surface-states, arising due to the coupling of surface transport with defect dynamics in bulk, determine the noise. We thus confirm that the measured low-frequency fluctuations in these films, over the entire temperature range of 20 mK–300 K, are determined primarily by bulk defect density. The magnitude of noise was comparable to that measured on bulk-exfoliated films but was slightly higher than that in MBE grown films. Our studies establish PLD as a viable route to develop high-quality topological insulator materials.
Band structure engineering is a powerful technique both for the design of new semiconductor materials and for imparting new functionalities to existing ones. In this article, we present a novel and versatile technique to achieve this by surface adsorption on low dimensional systems. As a specific example, we demonstrate, through detailed experiments and ab initio simulations, the controlled modification of band structure in ultrathin Te nanowires due to NO adsorption. Measurements of the temperature dependence of resistivity of single ultrathin Te nanowire field-effect transistor (FET) devices exposed to increasing amounts of NO reveal a gradual transition from a semiconducting to a metallic state. Gradual quenching of vibrational Raman modes of Te with increasing concentration of NO supports the appearance of a metallic state in NO adsorbed Te. Ab initio simulations attribute these observations to the appearance of midgap states in NO adsorbed Te nanowires. Our results provide fundamental insights into the effects of ambient on the electronic structures of low-dimensional materials and can be exploited for designing novel chemical sensors.
We present results of resistance fluctuation spectroscopy on single crystals of the predicted Kondo topological insulator material SmB 6 . Our measurements show that at low temperatures, transport in this system takes place only through surface states. The measured noise in this temperature range arises due to universal conductance fluctuations whose statistics was found to be consistent with theoretical predictions for that of two-dimensional systems in the symplectic symmetry class. At higher temperatures, we find signatures of glassy dynamics and establish that the measured noise is caused by mobility fluctuations in the bulk. We find that, unlike the topological insulators of the dichalcogenide family, the noises in surface and bulk conduction channels in SmB 6 are completely uncorrelated. Our measurements establish that at sufficiently low temperatures, the bulk has no discernible contribution to electrical transport in SmB 6 , making it an ideal platform for probing the physics of topological surface states.
Spins confined to atomically thin semiconductors are being actively explored as quantum information carriers. In transition metal dichalcogenides (TMDCs), the hexagonal crystal lattice gives rise to an additional valley degree of freedom with spin-valley locking and potentially enhanced spin life and coherence times. However, realizing well-separated single-particle levels and achieving transparent electrical contact to address them has remained challenging. Here, we report well-defined spin states in a few-layer MoS2 transistor, characterized with a spectral resolution of ∼50 μeV at T el = 150 mK. Ground state magnetospectroscopy confirms a finite Berry-curvature induced coupling of spin and valley, reflected in a pronounced Zeeman anisotropy, with a large out-of-plane g-factor of g ⊥ ≃ 8. A finite in-plane g-factor (g ∥ ≃ 0.55–0.8) allows us to quantify spin-valley locking and estimate the spin–orbit splitting 2ΔSO ∼ 100 μeV. The demonstration of spin-valley locking is an important milestone toward realizing spin-valley quantum bits.
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