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In this work, we present an angle-resolved photoemission spectroscopy study of a 1T′-WTe2 monolayer epitaxially grown on NbSe2 substrates, a prototypical quantum spin Hall insulator (QSHI)/superconductor heterojunction. Angle-resolved photoemission spectroscopy data indicate the formation of electronic states in the bulk bandgap of WTe2, which are absent in the nearly free-standing WTe2 grown on the highly oriented pyrolytic graphite substrate, where an energy gap of ∼100 meV is reported. The results are explained in terms of hybridization effects promoted by the QSHI-superconductor interaction at WTe2/NbSe2 interfaces, in line with recent scanning probe microscopy investigation and theoretical band structure calculations. Our findings highlight the important role of interlayer interaction on the electronic properties and ultimately on the engineering of topological properties of the QSHI/superconducting heterostructure. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) National Research Foundation (NRF) Published version This research was supported by the National Research Foundation (NRF) Singapore, under the Competitive Research Program “Toward On-Chip Topological Quantum Devices” (Grant No. NRFCRP21-2018-0001) F.B., H.K., I.V., and K.E.J.G. acknowledge the funding support from the Agency for Science, Technology and Research (Grant No. 21709). B.W. acknowledges support from the Singapore Ministry of Education (MOE) Academic Research Fund Tier 3 Grant (No. MOE2018-T3-1-002) and acknowledges the Singapore National Research Foundation (NRF) Fellowship (Grant No. NRF-NRFF2017-11).

Altres ajuts: J.Y., P.K., M.G.M., and Z.Z. acknowledge the computer resources at MareNostrum and the technical support provided by the Barcelona Supercomputing Center through Red Española de Supercomputación (Grants No. RES-FI-2020-1-0018, No. RES-FI-2020-1-0014, and No. RES-FI-2020-2-0039). ICN2 is funded by the Generalitat de Catalunya (CERCA Programme). We acknowledge a PRACE award granting access to MareNostrum4 at Barcelona Supercomputing Center (BSC), Spain (OptoSpin project id. 2020225411). We evidence the possibility for coherent electrical manipulation of the spin orientation of topologically protected edge states in a low-symmetry quantum spin Hall insulator. By using a combination of ab initio simulations, symmetry-based modeling, and large-scale calculations of the spin Hall conductivity, it is shown that small electric fields can efficiently vary the spin textures of edge currents in monolayer 1T'-WTe2 by up to a 90-degree spin rotation, without jeopardizing their topological character. These findings suggest a new kind of gate-controllable spin-based device, topologically protected against disorder and of relevance for the development of topological spintronics.

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY)., We report an intriguing transition from the quantum spin Hall phase to the spin Hall effect upon segregation of thallium adatoms adsorbed onto a graphene surface. Landauer-Büttiker and Kubo-Greenwood simulations are used to access both edge and bulk transport physics in disordered thallium-functionalized graphene systems of realistic sizes. Our findings not only quantify the detrimental effects of adatom clustering in the formation of the topological state, but also provide evidence for the emergence of spin accumulation at opposite sample edges driven by spin-dependent scattering induced by thallium islands, which eventually results in a minimum bulk conductivity ~4e2/h, insensitive to localization effects., S. R. acknowledges the Spanish Ministry of Economy and Competitiveness for funding (MAT2012-33911), the Severo Ochoa Program (MINECO SEV-2013-0295), and the Secretaria de Universidades e Investigación del Departamento de Economía y Conocimiento de la Generalidad de Cataluña. The research leading to these results has received funding from the European Union Seventh Framework Programme under Grant Agreement No. 604391 Graphene Flagship.

We report electrical conductance measurements of Bi nanocontacts created by repeated tip-surface indentation using a scanning tunneling microscope at temperatures of 4 and 300 K. As a function of the elongation of the nanocontact, we measure robust, tens of nanometers long plateaus of conductance G 0=2e2/h at room temperature. This observation can be accounted for by the mechanical exfoliation of a Bi(111) bilayer, a predicted quantum spin Hall (QSH) insulator, in the retracing process following a tip-surface contact. The formation of the bilayer is further supported by the additional observation of conductance steps below G0 before breakup at both temperatures. Our finding provides the first experimental evidence of the possibility of mechanical exfoliation of Bi bilayers, the existence of the QSH phase in a two-dimensional crystal, and, most importantly, the observation of the QSH phase at room temperature, We thank the Spanish MICINN for financial support through Grants No. FIS2010- 21883, No. FIS2011-23488, and No. CONSOLIDER CSD2007-0010, and Generalitat Valenciana through Grants No. ACCOMP/2012/127 and No. PROMETEO/ 2012/011. D. G.-M. acknowledges the Centro de Computación Científica at UAM for computational support. Cristina Almansa is gratefully acknowledged for her help with the transmission electron microscope