Suchergebnisse

Vertically stacked two-dimensional (2D) heterostructures composed of 2D semiconductors have attracted great attention. Most of these include hexagonal boron nitride (h-BN) as either a substrate, an encapsulant, or a tunnel barrier. However, reliable synthesis of large-area and epitaxial 2D heterostructures incorporating BN remains challenging. Here, we demonstrate the epitaxial growth of nominal monolayer (ML) MoSe2 on h-BN/Rh(111) by molecular beam epitaxy, where the MoSe2/h-BN layer system can be transferred from the growth substrate onto SiO2. The valence band structure of ML MoSe2/h-BN/Rh(111) revealed by photoemission electron momentum microscopy (kPEEM) shows that the valence band maximum located at the K point is 1.33 eV below the Fermi level (EF), whereas the energy difference between K and Γ points is determined to be 0.23 eV, demonstrating that the electronic properties, such as the direct band gap and the effective mass of ML MoSe2, are well preserved in MoSe2/h-BN heterostructures. ; The access was provided by the NFFA-Europe Infrastructure (proposal ID 121) under Horizon 2020 EU Funding Program. We thank N. Gambacorti for coordinating the access to the NFFA-EU program. This work was financially supported by the European Research Council (Grant No. 240076) and has received funding from the European Union's Horizon 2020 research and innovation programme under Grant Agreement Nos. 696656 and 785219 (Graphene Flagship Core 1 and Core 2). M.P. acknowledges support by the Swiss National Science Foundation (Grant No. 200021-162612). ; Peer reviewed

From Wiley via Jisc Publications Router ; History: received 2021-04-28, rev-recd 2021-06-16, pub-electronic 2021-08-08 ; Article version: VoR ; Publication status: Published ; Funder: European Union's Horizon 2020 research and innovation programme; Grant(s): 785219, 881603 ; Funder: EPSRC; Id: http://dx.doi.org/10.13039/501100000266; Grant(s): EP/L01548X ; Abstract: Superconductors with nontrivial band structure topology represent a class of materials with unconventional and potentially useful properties. Recent years have seen much success in creating artificial hybrid structures exhibiting the main characteristics of 2D topological superconductors. Yet, bulk materials known to combine inherent superconductivity with nontrivial topology remain scarce, largely because distinguishing their central characteristic—the topological surface states—has proved challenging due to a dominant contribution from the superconducting bulk. In this work, a highly anomalous behavior of surface superconductivity in topologically nontrivial 3D superconductor In2Bi, where the surface states result from its nontrivial band structure, itself a consequence of the non‐symmorphic crystal symmetry and strong spin–orbit coupling, is reported. In contrast to smoothly decreasing diamagnetic susceptibility above the bulk critical field, Hc2, as seen in conventional superconductors, a near‐perfect, Meissner‐like screening of low‐frequency magnetic fields well above Hc2 is observed. The enhanced diamagnetism disappears at a new phase transition close to the critical field of surface superconductivity, Hc3. Using theoretical modeling, the anomalous screening is shown to be consistent with modification of surface superconductivity by the topological surface states. The possibility of detecting signatures of the surface states using macroscopic magnetization provides a new tool for the discovery and identification of topological superconductors.

Chalcogen vacancies are generally considered to be the most common point defects in transition metal dichalcogenide (TMD) semiconductors because of their low formation energy in vacuum and their frequent observation in transmission electron microscopy studies. Consequently, unexpected optical, transport, and catalytic properties in 2D-TMDs have been attributed to in-gap states associated with chalcogen vacancies, even in the absence of direct experimental evidence. Here, we combine low-temperature non-contact atomic force microscopy, scanning tunneling microscopy and spectroscopy, and state-of-the-art ab initio density functional theory and GW calculations to determine both the atomic structure and electronic properties of an abundant chalcogen-site point defect common to MoSe and WS monolayers grown by molecular beam epitaxy and chemical vapor deposition, respectively. Surprisingly, we observe no in-gap states. Our results strongly suggest that the common chalcogen defects in the described 2D-TMD semiconductors, measured in vacuum environment after gentle annealing, are oxygen substitutional defects, rather than vacancies. ; This work was supported by the Center for Computational Study of Excited State Phenomena in Energy Materials (C2SEPEM), which is funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division under Contract No. DE-AC02-05CH11231, as part of the Computational Materials Sciences Program. Work performed at the Molecular Foundry was also supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under the same contract number. S.B. acknowledges fellowship support by the European Union under FP7-PEOPLE-2012-IOF-327581. S.B. and M.M.U acknowledge Spanish MINECO (MAT2017-88377-C2-1-R). S.R.A acknowledges Rothschild and Fulbright fellowships. B.S. appreciates support from the Swiss National Science Foundation under project number P2SKP2_171770. A.P. and O.V.Y. acknowledge support by the ERC Starting grant "TopoMat" (Grant No. 306504). M.F.C. acknowledges support from the U.S. National Science Foundation under project number EFMA-1542741. C.H. acknowledges support from NRF grant funded by the Korea government (MSIT) (No. 2018R1A2B6004538). DFT calculations were performed at the Swiss National Supercomputing Centre (CSCS) under project s832 and the facilities of Scientific IT and Application Support Center of EPFL. This research used resources of the National Energy Research Scientific Computing Center (NERSC), a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 for the GW calculations. This research used resources of the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231.