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Triplet–triplet upconversion enhanced by spin–orbit coupling in organic light-emitting diodes
摘要： Triplet–triplet upconversion, in which two triplet excitons are converted to one singlet exciton, is a well-known approach to exceed the limit of electroluminescence quantum efficiency in conventional fluorescence-based organic light-emitting diodes. Considering the spin multiplicity of triplet pairs, upconversion efficiency is usually limited to 20%. Although this limit can be exceeded when the energy of a triplet pair is lower than that of a second triplet excited state, such as for rubrene, it is generally difficult to engineer the energy levels of higher triplet excited states. Here, we investigate the upconversion efficiency of a series of new anthracene derivatives with different substituents. Some of these derivatives show upconversion efficiencies close to 50% even though the calculated energy levels of the second triplet excited states are lower than twice the lowest triplet energy. A possible upconversion mechanism is proposed based on the molecular structures and quantum chemical calculations.
关键词： Triplet–triplet upconversion,spin–orbit coupling,anthracene derivatives,quantum chemical calculations,organic light-emitting diodes
更新于2025-09-11 14:15:04
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Triplet exciton fine structure in Pt-rich polymers studied by circularly polarized emission under high magnetic field
摘要： Incorporating heavy atoms into polymer chains represents an effective way to generate emissive triplets. Here we used magneto-optical emission spectroscopy up to 17.5 Tesla for studying the fine structure of the triplet exciton in a series of Pt-rich π-conjugated polymers with various intrachain Pt concentrations. We found that their phosphorescence emission band shows substantial field-induced circular polarization (FICPO) up to 50% with an unusual, nonmonotonic field dependence at cryogenic temperature. From the field-induced energy splitting between left and right circularly polarized phosphorescence we obtained the effective g factor of triplet exciton varying in the range of ?0.13-0.85, which depends on the Pt concentration in the polymer chains. The FICPO of triplet emission originates from the population difference in spin sublevels, which is determined by thermal equilibrium subjected to spin-orbit coupling (SOC), exchange, and Zeeman interactions. Surprisingly we also observed FICPO in the fluorescence emission that results from the singlet-triplet interaction caused by the strong SOC. From these results we extracted the various interaction parameters that describe the exciton fine structure in these Pt-contained compounds.
关键词： Pt-rich polymers,high magnetic field,circularly polarized emission,spin-orbit coupling,triplet exciton
更新于2025-09-11 14:15:04
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Single Crystal Growth and Characterization of the Chalcopyrite Semiconductor CuInTe2 for Photoelectrochemical Solar Fuel Production
摘要： Transition metal chalcogenides are a promising family of materials for applications as photocathodes in photoelectrochemical (PEC) H2 generation. A long-standing challenge for chalcopyrite semiconductors is characterizing their electronic structure—both experimentally and theoretically—due to their relatively high energy bandgaps and spin orbit coupling (SOC), respectively. In this work, we present single crystals of CuInTe2, whose relatively small optically measured bandgap of 0.9 ± 0.03 eV enables electronic structure characterization by angle-resolved photoelectron spectroscopy (ARPES) in conjunction with first-principle calculations incorporating SOC. ARPES measurements reveal bands that are steeply dispersed in energy with a band velocity of 2.5-5.4 x 105 m/s, almost 50% of the extremely conductive material graphene. Additionally, CuInTe2 single crystals are fabricated into electrodes to experimentally determine the valence band edge energy and confirm the thermodynamic suitability of CuInTe2 for water redox chemistry. The electronic structure characterization and band edge position presented in this work provide kinetic and thermodynamic factors that support CuInTe2 as a strong candidate for water reduction.
关键词： photoelectrochemical H2 generation,electronic structure,spin orbit coupling,chalcopyrite semiconductors,band velocity,valence band edge energy,Transition metal chalcogenides,angle-resolved photoelectron spectroscopy,water redox chemistry,CuInTe2
更新于2025-09-10 09:29:36
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SU(3) topological insulators in the honeycomb lattice
摘要： We investigate realizations of topological insulators with spin-1 bosons loaded in a honeycomb optical lattice and subjected to a SU(3) spin-orbit coupling—a situation which can be realized experimentally using cold atomic gases. In this paper, we focus on the topological properties of the single-particle band structure, namely, Chern numbers (lattice with periodic boundary conditions) and edge states (lattice with strip geometry) and their connection to time-reversal symmetry and the sublattice symmetry. While SU(2) spin-orbit couplings always lead to time-reversal symmetric tight-binding models, and thereby to topologically trivial band structures, suitable SU(3) spin-orbit couplings can break time-reversal symmetry and lead to topologically nontrivial bulk band structures and to edge states in the strip geometry. In addition, we show that one can trigger a series of topological transitions (i.e., integer changes of the Chern numbers) that are speci?c to the geometry of the honeycomb lattice by varying a single parameter in the Hamiltonian.
关键词： sublattice symmetry,SU(3) spin-orbit coupling,honeycomb optical lattice,spin-1 bosons,time-reversal symmetry,edge states,topological insulators,Chern numbers
更新于2025-09-09 09:28:46
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[IEEE 2018 Open Innovations (OI) - South Africa (2018.10.3-2018.10.5)] 2018 Open Innovations Conference (OI) - Effect of Dipole Corrections and Spin Orbit Coupling on Tungsten Dichalcogenides Monolayer: A in Silico First Principles Study
摘要： The structural and electronic properties of tungsten dichalogenides compounds (WS2, WSe2, WTe2) were investigated from first principles calculations. We found that the structural and electronic properties changed both as a function of the dipole corrections and spin-orbit coupling (SOC). Comparing the calculated results with experimental values, we found that introducing SOC in these 2D materials grossly underestimates the electronic band gap. Adding the self-consistent dipole correction results in larger electronic band gap for these tungsten dichalogenide compounds. Thus, the influence of dipole corrections in these 2D WX2 materials was found to be significant. The SOC are not relevant for these materials and care should be taken on application of these dipole corrections itself.
关键词： tungsten dichalogenides,spin orbit coupling,monolayer,dipole correction
更新于2025-09-09 09:28:46
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Spin orbit coupling induced band gap in gemanene modulated by external field
摘要： We investigate the electronic band structure of germanene crystal by using the sixteen band tight-binding calculation. We focus on the modulation of its band gap with spin–orbit coupling (SOC), perpendicular electric ?eld and magnetic ?eld. Our calculation shows that the SOC opens a tunable band gap in the Dirac-type electronic structures, and plays a crucial rule in the formation of the energy band gap. The in?uence of SOC on the gap in germanene is much larger than that in graphene, which makes germanene an ideal candidate to exhibit the quantum spin Hall effect at room temperature. We also ?nd that the electronic structure and topological property of germanene can be tuned by the external ?eld signi?cantly. Thus the electronic structure of germanene can be controlled to produce metallic, semiconducting, or insulating properties by applying an appropriate external ?eld. In addition, the key features of the band structure induced by the electrical ?eld and magnetic ?eld are quite different. For the electric ?eld applied, two spin-up states produce a gap at K point, in contrast, two spin-down states do it at K′ points. While for the magnetic ?eld present, the band gaps are formed by the spin-up states from the conduction band and spin-down state from the valance band at both the K and K′ points. This modulation behavior of the band gap by the external ?eld paves a way to the realization of germanene based spintronic devices.
关键词： topological insulator,electronic structure,tight-binding model,germanene,spin-orbit coupling
更新于2025-09-09 09:28:46
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across the quantum phase transition from topological to trivial insulator
摘要： Using spin- and angle-resolved photoemission spectroscopy and relativistic many-body calculations, we investigate the evolution of the electronic structure of (Bi1?xInx )2Se3 bulk single crystals around the critical point of the trivial to topological insulator quantum-phase transition. By increasing x, we observe how a surface gap opens at the Dirac point of the initially gapless topological surface state of Bi2Se3, leading to the existence of massive fermions. The surface gap monotonically increases for a wide range of x values across the topological and trivial sides of the quantum-phase transition. By means of photon-energy-dependent measurements, we demonstrate that the gapped surface state survives the inversion of the bulk bands which occurs at a critical point near x = 0.055. The surface state exhibits a nonzero in-plane spin polarization which decays exponentially with increasing x, and which persists in both the topological and trivial insulator phases. Our calculations reveal qualitative agreement with the experimental results all across the quantum-phase transition upon the systematic variation of the spin-orbit coupling strength. A non-time-reversal symmetry-breaking mechanism of bulk-mediated scattering processes that increase with decreasing spin-orbit coupling strength is proposed as explanation.
关键词： quantum-phase transition,topological insulator,electronic structure,photoemission spectroscopy,spin-orbit coupling
更新于2025-09-09 09:28:46
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heterostructures
摘要： The weak intrinsic spin-orbit coupling in graphene can be greatly enhanced by proximity coupling. Here, we report on the proximity-induced spin-orbit coupling in graphene transferred by hexagonal boron nitride (hBN) onto the topological insulator Bi1.5Sb0.5Te1.7Se1.3 (BSTS) which was grown on a hBN substrate by vapor solid synthesis. Phase coherent transport measurements, revealing weak localization, allow us to extract the carrier density-dependent phase coherence length lφ. While lφ increases with increasing carrier density in the hBN/graphene/hBN reference sample, it decreases in graphene/BSTS due to the proximity coupling of BSTS to graphene. The latter behavior results from D’yakonov-Perel’-type spin scattering in graphene with a large proximity-induced spin-orbit coupling strength of at least 2.5 meV.
关键词： weak localization,topological insulator,graphene,proximity effect,spin-orbit coupling
更新于2025-09-09 09:28:46
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Nonreciprocal Optical and Magnetooptical Effects in Semiconductor Quantum Wells
摘要： Effects implying violation of the Fresnel light reflection laws in semiconductor structures with quantum wells (QWs) have been investigated. This violation is related to the manifestation of spatial dispersion caused by spin–orbit coupling in structures without inversion centers. The spin–orbit coupling constants characterizing polarization conversion in symmetric and asymmetric structures with QWs have been measured.
关键词： spatial dispersion,nonreciprocal optical effects,polarization conversion,spin–orbit coupling,semiconductor quantum wells,magnetooptical effects
更新于2025-09-09 09:28:46
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Weak Antilocalization at the Atomic-Scale Limit of Metal Film Thickness
摘要： Creation of the 2D metallic layers with the thickness as small as a few atomic layers and investigation of their properties are interesting and challenging tasks of the modern condensed-matter physics. One of the possible ways to grow such layers resides in the synthesis of the so-called metal-induced reconstructions on silicon (i.e., silicon substrates covered with ordered metal ?lms of monolayer or submonolayer thickness). The 2D Au?Tl compound on Si(111) surface having 7×7 periodicity belongs to the family of the reconstructions incorporating heavy-metal atoms with a strong spin?orbit coupling (SOC). In such systems, strong SOC results in the spin-splitting of surface-state bands due to the Rashba e?ect, the occurrence of which was experimentally proved. Another remarkable consequence of a strong SOC that manifests itself in the transport properties is a weak antilocalization (WAL) e?ect, which has never been explored in the metal layers of atomic thickness. In the present study, the transport and magnetotransport properties of the 2D Au?Tl compound on Si(111) surface were investigated at low temperatures down to ～2.0 K. The compound was proved to show behavior of the 2D nearly free electron gas system with metallic conduction, as indicated by Io?e?Regel criterion. It demonstrates the WAL e?ect which is interpreted in the framework of Hikami?Larkin?Nagaoka theory, and possible mechanisms of the electron decoherence are discussed. Bearing in mind that besides the (Au, Tl)/Si(111) 7×7 system, there are many other ordered atomic-layer metal ?lms on silicon di?ering by composition, structure, strength of SOC, and spin texture, which provide a promising area for prospective investigations of the WAL e?ect at the atomic-scale limit when the ?lm thickness is less than the electron wavelength.
关键词： weak antilocalization (WAL),2D compounds,transport measurements,magnetoresistance,strong spin?orbit coupling (SOC)
更新于2025-09-09 09:28:46