10 research outputs found
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The Weak 3D Topological Insulator Bi12Rh3Sn3I9
Topological insulators (TIs) gained high interest due to their protected electronic surface states that allow dissipation-free electron and information transport. In consequence, TIs are recommended as materials for spintronics and quantum computing. Yet, the number of well-characterized TIs is rather limited. To contribute to this field of research, we focused on new bismuth-based subiodides and recently succeeded in synthesizing a new compound Bi12Rh3Sn3I9, which is structurally closely related to Bi14Rh3I9 â a stable, layered material. In fact, Bi14Rh3I9 is the first experimentally supported weak 3D TI. Both structures are composed of well-defined intermetallic layers of â2[(Bi4Rh)3I]2+ with topologically protected electronic edge-states. The fundamental difference between Bi14Rh3I9 and Bi12Rh3Sn3I9 lies in the composition and the arrangement of the anionic spacer. While the intermetallic 2D TI layers in Bi14Rh3I9 are isolated by â1[Bi2I8]2â chains, the isoelectronic substitution of bismuth(III) with tin(II) leads to â2[Sn3I8]2â layers as anionic spacers. First transport experiments support the 2D character of this material class and revealed metallic conductivity. © 2020 The Authors. Published by Wiley-VCH Gmb
BiââRhâCuâIâ : A 3D Weak Topological Insulator with Monolayer Spacers and Independent Transport Channels
Topological insulators (TIs) are semiconductors with protected electronic surface states that allow dissipation-free transport. TIs are envisioned as ideal materials for
spintronics and quantum computing. In Bi14Rh3I9, the first weak 3D TI, topology presumably arises from stacking of the intermetallic [(Bi4Rh)3I]2ĂŸ layers, which are
predicted to be 2D TIs and to possess protected edge-states, separated by topologically trivial [Bi2I8]2+ octahedra chains. In the new layered salt Bi12Rh3Cu2I5, the same intermetallic layers are separated by planar, i.e., only one atom thick, [Cu2I4]2- anions. Density functional theory (DFT)-based calculations show that the compound is a weak 3D TI, characterized by Z2 ÂŒ Ă°0; 0001Ă, and that the topological gap is generated by strong spinâorbit coupling (Eg,calc.~ 10 meV). According to a bonding analysis, the copper cations prevent strong coupling between the TI layers. The calculated surface spectral function for a finite-slab geometry shows distinct characteristics for the two terminations of the main crystal faces â©001âȘ, viz., [(Bi4Rh)3I]2ĂŸ and [Cu2I4]2-. Photoelectron spectroscopy data confirm the calculated band structure. In situ four-point probe measurements indicate a highly anisotropic bulk semiconductor (Eg,exp.ÂŒ 28 meV) with pathindependent metallic conductivity restricted to the surface as well as temperatureindependent
conductivity below 60 K
Surface Transport Properties of Pb-Intercalated Graphene
Intercalation experiments on epitaxial graphene are attracting a lot of attention at present as a tool to further boost the electronic properties of 2D graphene. In this work, we studied the intercalation of Pb using buffer layers on 6H-SiC(0001) by means of electron diffraction, scanning tunneling microscopy, photoelectron spectroscopy and in situ surface transport. Large-area intercalation of a few Pb monolayers succeeded via surface defects. The intercalated Pb forms a characteristic striped phase and leads to formation of almost charge neutral graphene in proximity to a Pb layer. The Pb intercalated layer consists of 2 ML and shows a strong structural corrugation. The epitaxial heterostructure provides an extremely high conductivity of σ=100 mS/□. However, at low temperatures (70 K), we found a metal-insulator transition that we assign to the formation of minigaps in epitaxial graphene, possibly induced by a static distortion of graphene following the corrugation of the interface layer
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Education and Genetic Risk Modulate Hippocampal Structure in Alzheimerâs Disease
Genetic and environmental protective factors and risks modulate brain structure and function in neurodegenerative diseases and their preclinical stages. We wanted to investigate whether the years of formal education, a proxy measure for cognitive reserve, would influence hippocampal structure in Alzheimerâs disease patients, and whether apolipoprotein EΔ4 (APOE4) carrier status and a first-degree family history of the disease would change a possible association. Fifty-eight Alzheimerâs disease patients underwent 3T magnetic resonance imaging. We applied a cortical unfolding approach to investigate individual subregions of the medial temporal lobe. Among patients homozygous for the APOE4 genotype or carrying both APOE4 and family history risks, lower education was associated with a thinner cortex in multiple medial temporal regions, including the hippocampus. Our data suggest that the years of formal education and genetic risks interact in their influence on hippocampal structure in Alzheimerâs disease patients
Education and Genetic Risk Modulate Hippocampal Structure in Alzheimerâs Disease
Genetic and environmental protective factors and risks modulate brain structure and function in neurodegenerative diseases and their preclinical stages. We wanted to investigate whether the years of formal education, a proxy measure for cognitive reserve, would influence hippocampal structure in Alzheimerâs disease patients, and whether apolipoprotein EΔ4 (APOE4) carrier status and a first-degree family history of the disease would change a possible association. Fifty-eight Alzheimerâs disease patients underwent 3T magnetic resonance imaging. We applied a cortical unfolding approach to investigate individual subregions of the medial temporal lobe. Among patients homozygous for the APOE4 genotype or carrying both APOE4 and family history risks, lower education was associated with a thinner cortex in multiple medial temporal regions, including the hippocampus. Our data suggest that the years of formal education and genetic risks interact in their influence on hippocampal structure in Alzheimerâs disease patients
Bi 12 Rh 3 Cu 2 I 5 : A 3D Weak Topological Insulator with Monolayer Spacers and Independent Transport Channels
Topological insulators (TIs) are semiconductors with protected electronic surface states that allow dissipation-free transport. TIs are envisioned as ideal materials for spintronics and quantum computing. In Bi14Rh3I9, the first weak 3D TI, topology presumably arises from stacking of the intermetallic [(Bi4Rh)(3)I](2+) layers, which are predicted to be 2D TIs and to possess protected edge-states, separated by topologically trivial [Bi2I8](2-) octahedra chains. In the new layered salt Bi12Rh3Cu2I5, the same intermetallic layers are separated by planar, i.e., only one atom thick, [Cu2I4](2-) anions. Density functional theory (DFT)-based calculations show that the compound is a weak 3D TI, characterized by Z 2 = ( 0 ; 0001 ) , and that the topological gap is generated by strong spin-orbit coupling (E (g,calc.) similar to 10 meV). According to a bonding analysis, the copper cations prevent strong coupling between the TI layers. The calculated surface spectral function for a finite-slab geometry shows distinct characteristics for the two terminations of the main crystal faces ⟨001⟩, viz., [(Bi4Rh)(3)I](2+) and [Cu2I4](2-). Photoelectron spectroscopy data confirm the calculated band structure. In situ four-point probe measurements indicate a highly anisotropic bulk semiconductor (E (g,exp.) = 28 meV) with path-independent metallic conductivity restricted to the surface as well as temperature-independent conductivity below 60 K
Topological Surface State in Epitaxial Zigzag Graphene Nanoribbons
Protected and spin-polarized transport channels are the hallmark of topological insulators, coming along with an intrinsic strong spin-orbit coupling. Here we identified such corresponding chiral states in epitaxially grown zigzag graphene nanoribbons (zz-GNRs), albeit with an extremely weak spin-orbit interaction. While the bulk of the monolayer zz-GNR is fully suspended across a SiC facet, the lower edge merges into the SiC(0001) substrate and reveals a surface state at the Fermi energy, which is extended along the edge and splits in energy toward the bulk. All of the spectroscopic details are precisely described within a tight binding model incorporating a Haldane term and strain effects. The concomitant breaking of time-reversal symmetry without the application of external magnetic fields is supported by ballistic transport revealing a conduction of G = e2/h