| 1. |
- Bray, C., et al.
(författare)
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Temperature-dependent zero-field splittings in graphene
- 2022
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 106:24
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Tidskriftsartikel (refereegranskat)abstract
- Graphene is a quantum spin Hall insulator with a 45μeV-wide nontrivial topological gap induced by the intrinsic spin-orbit coupling. Even though this zero-field spin splitting is weak, it makes graphene an attractive candidate for applications in quantum technologies, given the resulting long spin-relaxation time. On the other side, the staggered sublattice potential, resulting from the coupling of graphene with its boron nitride substrate, compensates intrinsic spin-orbit coupling and decreases the nontrivial topological gap, which may lead to the phase transition into trivial band insulator state. In this work, we present extensive experimental studies of the zero-field splittings in monolayer and bilayer graphene in a temperature range 2-12 K by means of subterahertz photoconductivity-based electron spin-resonance technique. Surprisingly, we observe a decrease of the spin splittings with increasing temperature. We discuss the origin of this phenomenon by considering possible physical mechanisms likely to induce a temperature dependence of the spin-orbit coupling. These include the difference in the expansion coefficients between the graphene and the boron nitride substrate or the metal contacts, the electron-phonon interactions, and the presence of a magnetic order at low temperature. Our experimental observation expands knowledge about the nontrivial topological gap in graphene.
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| 2. |
- Maussang, K., et al.
(författare)
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Temperature dependance of Intrinsic Spin Orbit Coupling Gap in Graphene probed by Terahertz photoconductivity
- 2023
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Ingår i: International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz. - 2162-2027 .- 2162-2035.
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Konferensbidrag (refereegranskat)abstract
- Graphene is a quantum spin Hall insulator, with a nontrivial topological gap induced by the spin-orbit coupling. Such splitting is weak (∼ 45 μ eV) in the absence of external magnetic field. However, due to rather long spin-relaxation time, graphene is an attractive candidate for applications in quantum technologies. When it is encapsulated in hexagonal boron nitride, the coupling between graphene and the substrate compensates intrinsic spin-orbit coupling and decreases the nontrivial topological gap, which may lead to phase transition into a trivial band insulator state. In this work, we have measured experimentally the zero-field splittings in monolayer and bilayer graphene by the means of subterahertz photoconductivity-based electron spin resonance technique. The dependance in temperature of such splittings have been also studied in the 2-12K range. We observed a decrease of the spin splittings with increasing temperature. Such behavior might be understood from several physical mechanisms that could induce a temperature dependence of the spin-orbit coupling. These includes the difference in the expansion coefficients between the graphene and the boron nitride substrate or the metal contacts, the electronphonon interactions, and the presence of a magnetic order at low temperature.
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| 3. |
- Darakchieva, Vanya, et al.
(författare)
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Free electron properties and hydrogen in InN grown by MOVPE
- 2011
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Ingår i: PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE. - : WILEY-BLACKWELL, COMMERCE PLACE, 350 MAIN ST, MALDEN 02148, MA USA. - 1862-6300. ; 208:5, s. 1179-1182
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Tidskriftsartikel (refereegranskat)abstract
- In this work we present a comprehensive study on the hydrogen impurities, free electron, and structural properties of MOVPE InN films with state-of-the-art quality. We find a correlation between the decrease of free electron concentration and the reduction of bulk hydrogen in the films upon thermal annealing, while no changes in the dislocation densities and strain are observed. Our results suggest that hydrogen is a major source for the unintentional n-type doping in MOVPE InN.
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| 4. |
- Darakchieva, Vanya, et al.
(författare)
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Unintentional incorporation of H and related structural and free-electron properties of c- and a-plane InN
- 2012
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Ingår i: PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE. - : Wiley-VCH Verlag Berlin. - 1862-6300. ; 209:1, s. 91-94
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we present a comprehensive study on the hydrogen impurity depth profiles in InN films with polar c-plane and nonpolar a-plane surface orientations in relation to their structural and free-electron properties. We find that the as-grown nonpolar films exhibit generally higher bulk and near-surface H concentrations compared to the polar InN counter-parts. The latter may be partly associated with a change in the growth mode from 2D to 3D and a decrease in the grain size. Thermal annealing leads to a reduction of H concentrations and the intrinsic H levels are influenced by the structural characteristics of the films. The factors allowing reduction of bulk H and free electron concentrations in a-plane films are discussed.
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