5 results
Search Results
Now showing 1 - 5 of 5
- ItemA thiazolo[5,4-: D] thiazole-bridged porphyrin organic framework as a promising nonlinear optical material(London : Royal Society of Chemistry (RSC), 2019) Samal, Mahalaxmi; Valligatla, Sreeramulu; Saad, Nabil A.; Rao, M. Veeramohan; Rao, D. Narayana; Sahu, Rojalin; Biswal, Bishnu P.Porphyrin-based porous organic frameworks are an important group of materials gaining interest due to their structural diversity and distinct opto-electronic properties. However, these materials are seldom explored for nonlinear optical (NLO) applications. In this work, we investigate a thiazolo[5,4-d]thiazole-bridged porous, porphyrin framework (Por-TzTz-POF) with promising NLO properties. The planar TzTz moiety coupled with integrated porphyrin units enables efficient π-conjugation and charge distribution in the Por-TzTz-POF resulting in a high nonlinear absorption coefficient (β = 1100 cm GW-1) with figure of merit (FoM) σ1/σ0 = 5571, in contrast to analogous molecules and material counterparts e.g. metal-organic frameworks (MOFs; β = ∼0.3-0.5 cm GW-1), molecular porphyrins (β = ∼100-400 cm GW-1), graphene (β = 900 cm GW-1), and covalent organic frameworks (Por-COF-HH; β = 1040 cm GW-1 and FoM = 3534). This journal is © The Royal Society of Chemistry.
- ItemAnharmonic strong-coupling effects at the origin of the charge density wave in CsV3Sb5([London] : Nature Publishing Group UK, 2024) He, Ge; Peis, Leander; Cuddy, Emma Frances; Zhao, Zhen; Li, Dong; Zhang, Yuhang; Stumberger, Romona; Moritz, Brian; Yang, Haitao; Gao, Hongjun; Devereaux, Thomas Peter; Hackl, RudiThe formation of charge density waves is a long-standing open problem, particularly in dimensions higher than one. Various observations in the vanadium antimonides discovered recently further underpin this notion. Here, we study the Kagome metal CsV3Sb5 using polarized inelastic light scattering and density functional theory calculations. We observe a significant gap anisotropy with 2Δmax/kBTCDW≈20, far beyond the prediction of mean-field theory. The analysis of the A1g and E2g phonons, including those emerging below TCDW, indicates strong phonon-phonon coupling, presumably mediated by a strong electron-phonon interaction. Similarly, the asymmetric Fano-type lineshape of the A1g amplitude mode suggests strong electron-phonon coupling below TCDW. The large electronic gap, the enhanced anharmonic phonon-phonon coupling, and the Fano shape of the amplitude mode combined are more supportive of a strong-coupling phonon-driven charge density wave transition than of a Fermi surface instability or an exotic mechanism in CsV3Sb5.
- ItemLarge magneto-Seebeck effect in magnetic tunnel junctions with half-metallic Heusler electrodes(London : Nature Publishing Group, 2017) Boehnke, A.; Martens, U.; Sterwerf, C.; Niesen, A.; Huebner, T.; Von Der Ehe, M.; Meinert, M.; Kuschel, T.; Thomas, A.; Heiliger, C.; Münzenberg, M.; Reiss, G.Spin caloritronics studies the interplay between charge-, heat- and spin-currents, which are initiated by temperature gradients in magnetic nanostructures. A plethora of new phenomena has been discovered that promises, e.g., to make wasted heat in electronic devices useable or to provide new read-out mechanisms for information. However, only few materials have been studied so far with Seebeck voltages of only some microvolt, which hampers applications. Here, we demonstrate that half-metallic Heusler compounds are hot candidates for enhancing spin-dependent thermoelectric effects. This becomes evident when considering the asymmetry of the spin-split density of electronic states around the Fermi level that determines the spin-dependent thermoelectric transport in magnetic tunnel junctions. We identify Co2FeAl and Co2FeSi Heusler compounds as ideal due to their energy gaps in the minority density of states, and demonstrate devices with substantially larger Seebeck voltages and tunnel magneto-Seebeck effect ratios than the commonly used Co-Fe-B-based junctions.
- ItemSingle molecule magnet with an unpaired electron trapped between two lanthanide ions inside a fullerene(London : Nature Publishing Group, 2017) Liu, F.; Krylov, D.S.; Spree, L.; Avdoshenko, S.M.; Samoylova, N.A.; Rosenkranz, M.; Kostanyan, A.; Greber, T.; Wolter, A.U.B.; Büchner, B.; Popov, A.A.Increasing the temperature at which molecules behave as single-molecule magnets is a serious challenge in molecular magnetism. One of the ways to address this problem is to create the molecules with strongly coupled lanthanide ions. In this work, endohedral metallofullerenes Y 2 @C 80 and Dy 2 @C 80 are obtained in the form of air-stable benzyl monoadducts. Both feature an unpaired electron trapped between metal ions, thus forming a single-electron metal-metal bond. Giant exchange interactions between lanthanide ions and the unpaired electron result in single-molecule magnetism of Dy 2 @C 80 (CH 2 Ph) with a record-high 100 s blocking temperature of 18 K. All magnetic moments in Dy 2 @C 80 (CH 2 Ph) are parallel and couple ferromagnetically to form a single spin unit of 21 μ B with a dysprosium-electron exchange constant of 32 cm -1. The barrier of the magnetization reversal of 613 K is assigned to the state in which the spin of one Dy centre is flipped.
- ItemFinite temperature fluctuation-induced order and responses in magnetic topological insulators(College Park, MD : APS, 2021) Scholten, Marius; Facio, Jorge I.; Ray, Rajyavardhan; Eremin, Ilya M.; van den Brink, Jeroen; Nogueira, Flavio S.We derive an effective field theory model for magnetic topological insulators and predict that a magnetic electronic gap persists on the surface for temperatures above the ordering temperature of the bulk. Our analysis also applies to interfaces of heterostructures consisting of a ferromagnetic and a topological insulator. In order to make quantitative predictions for MnBi2Te4 and for EuS-Bi2Se3 heterostructures, we combine the effective field theory method with density functional theory and Monte Carlo simulations. For MnBi2Te4 we predict an upwards Néel temperature shift at the surface up to 15%, while the EuS-Bi2Se3 interface exhibits a smaller relative shift. The effective theory also predicts induced Dzyaloshinskii-Moriya interactions and a topological magnetoelectric effect, both of which feature a finite temperature and chemical potential dependence.