| 1. |
- Riley, J. M., et al.
(author)
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Direct observation of spin-polarized bulk bands in an inversion-symmetric semiconductor
- 2014
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In: Nature Physics. - 1745-2473. ; 10:11, s. 835-839
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Journal article (peer-reviewed)abstract
- Methods to generate spin-polarized electronic states in nonmagnetic solids are strongly desired to enable all-electrical manipulation of electron spins for new quantum devices(1). This is generally accepted to require breaking global structural inversion symmetry(1-5). In contrast, here we report the observation from spin- and angle-resolved photoemission spectroscopy of spin-polarized bulk states in the centrosymmetric transition-metal dichalcogenide WSe2. Mediated by a lack of inversion symmetry in constituent structural units of the bulk crystal where the electronic states are localized(6), we show how spin splittings up to similar to 0.5 eV result, with a spin texture that is strongly modulated in both real and momentum space. Through this, our study provides direct experimental evidence for a putative locking of the spin with the layer and valley pseudospins in transition-metal dichalcogenides(7,8), of key importance for using these compounds in proposed valleytronic devices.
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| 2. |
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| 3. |
- Ndiaye, W., et al.
(author)
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Bulk electronic structure of Mn5Ge3/Ge(111) films by angle-resolved photoemission spectroscopy
- 2013
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 87:16
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Journal article (peer-reviewed)abstract
- Mn5Ge3(001) thin films grown on Ge(111)-c(2 x 8) reconstructed surfaces were studied by angle-resolved photoemission using synchrotron radiation in the 14-94 eV photon energy range. The results obtained in the Gamma ALM plane and in the Gamma AHK plane are in agreement with simulations starting with band structure calculations based on the density functional theory. This provides a unique validation of band structure calculations for a proper description of the electronic properties of Mn5Ge3. Only the spectral feature very close to the Fermi level cannot be well explained by the simulation. This departure is discussed in terms of the three-dimensional nature of the sample and of correlation effects.
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| 4. |
- Berntsen, Magnus H., et al.
(author)
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A spin- and angle-resolving photoelectron spectrometer
- 2010
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In: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 81:3
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Journal article (peer-reviewed)abstract
- A new type of hemispherical electron energy analyzer that permits angle and spin resolved photoelectron spectroscopy has been developed. The analyzer permits standard angle resolved spectra to be recorded with a two-dimensional detector in parallel with spin detection using a mini-Mott polarimeter. General design considerations as well as technical solutions are discussed and test results from the Au(111) surface state are presented.
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| 5. |
- Malyshev, O. B., et al.
(author)
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Ar beam induced desorption from different materials at TSL
- 2010
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In: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 85:2, s. 338-343
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Journal article (peer-reviewed)abstract
- This paper describes new experiments on the heavy ion desorption yield measurements with 5 MeV/u Ar8+ and summarizes all results of experiments with 5 MeV/u Ar8+ performed at The Svedberg Laboratory in Uppsala (Sweden). These results are important for the update and design of the FAIR facility at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt (Germany) where the required increase in beam intensity is limited by ion induced pressure instability. It was shown that lowest desorption yields can be achieved with gold coatings, whereas grazing incident loss increases the desorption yield by roughly an order of magnitude compared to perpendicular loss. The desorption yield of saturated NEG samples was measured to be higher compared to any non pumping samples. The desorption yield of copper can be lower and higher compared to stainless steel depending on cleaning procedure and sample history. Additionally the secondary electron and ion yield was measured to be a few tens of electrons and ions emitted per projectile impact in backward direction. Their influence on the desorption yield due to secondary effects was less than 5% compared to the primary desorption by the high energetic projectile. (C) 2010 Elsevier Ltd. All rights reserved.
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| 6. |
- Neupane, Madhab, et al.
(author)
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Observation of quantum-tunnelling-modulated spin texture in ultrathin topological insulator Bi2Se3 films.
- 2014
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5
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Journal article (peer-reviewed)abstract
- Understanding the spin-texture behaviour of boundary modes in ultrathin topological insulator films is critically essential for the design and fabrication of functional nanodevices. Here, by using spin-resolved photoemission spectroscopy with p-polarized light in topological insulator Bi2Se3 thin films, we report tunnelling-dependent evolution of spin configuration in topological insulator thin films across the metal-to-insulator transition. We report a systematic binding energy- and wavevector-dependent spin polarization for the topological surface electrons in the ultrathin gapped-Dirac-cone limit. The polarization decreases significantly with enhanced tunnelling realized systematically in thin insulating films, whereas magnitude of the polarization saturates to the bulk limit faster at larger wavevectors in thicker metallic films. We present a theoretical model that captures this delicate relationship between quantum tunnelling and Fermi surface spin polarization. Our high-resolution spin-based spectroscopic results suggest that the polarization current can be tuned to zero in thin insulating films forming the basis for a future spin-switch nanodevice.
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| 7. |
- Wojek, Bastian M., et al.
(author)
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Spin-polarized (001) surface states of the topological crystalline insulator Pb0.73Sn0.27Se
- 2013
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 87:11, s. 115106-
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Journal article (peer-reviewed)abstract
- We study the nature of (001) surface states in Pb0.73Sn0.27Se in the newly discovered topological-crystalline-insulator (TCI) phase as well as the corresponding topologically trivial state above the band-gap-inversion temperature. Our calculations predict not only metallic surface states with a nontrivial chiral spin structure for the TCI case, but also nonmetallic (gapped) surface states with nonzero spin polarization when the system is a normal insulator. For both phases, angle- and spin-resolved photoelectron spectroscopy measurements provide conclusive evidence for the formation of these (001) surface states in Pb0.73Sn0.27Se, as well as for their chiral spin structure.
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| 8. |
- Xu, Su-Yang, et al.
(author)
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Hedgehog spin texture and Berry's phase tuning in a magnetic topological insulator
- 2012
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In: Nature Physics. - 1745-2473. ; 8:8, s. 616-622
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Journal article (peer-reviewed)abstract
- Understanding and control of spin degrees of freedom on the surfaces of topological materials are key to future applications as well as for realizing novel physics such as the axion electrodynamics associated with time-reversal (TR) symmetry breaking on the surface. We experimentally demonstrate magnetically induced spin reorientation phenomena simultaneous with a Dirac-metal to gapped-insulator transition on the surfaces of manganese-doped Bi2Se3 thin films. The resulting electronic groundstate exhibits unique hedgehog-like spin textures at low energies, which directly demonstrate the mechanics of TR symmetry breaking on the surface. We further show that an insulating gap induced by quantum tunnelling between surfaces exhibits spin texture modulation at low energies but respects TR invariance. These spin phenomena and the control of their Fermi surface geometrical phase first demonstrated in our experiments pave the way for the future realization of many predicted exotic magnetic phenomena of topological origin.
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