Enhancement Of Spin-orbit Coupling Research Articles

Ultrafast spin-flip exciton conversion and narrowband sky-blue luminescence in a fused polycyclic selenaborin emitter.

Thermally activated delayed fluorescence (TADF) materials with high photoluminescence quantum yields and fast reverse intersystem crossing (RISC) capabilities are highly desirable for applications in high-efficiency organic light-emitting diodes. Herein, we report the synthesis as well as structural and photophysical properties of 5,9-diselena-13b-boranaphtho[3,2,1-de]anthracene (SeBSe) as a narrowband-emissive TADF material. The incorporation of two selenium atoms into the boron-fused pentacyclic π-core results in a small singlet-triplet energy gap (ΔE ST) and thereby significant TADF properties. Moreover, theoretical calculations revealed a noticeable spin-orbit coupling enhancement between the singlet and triplet manifolds in SeBSe by virtue of the heavy-atom effect of selenium atoms. Consequently, SeBSe allows ultrafast spin-flip RISC with the rate constant surpassing 108 s-1, which far exceeds the corresponding fluorescence radiative decay rate (∼106 s-1), enabling an ideal singlet-triplet superimposed excited state.

Enhanced thermoelectric performance in cubic SnSe-based alloys via manipulation of grain boundary scattering and phonon transport

Owing to the strong anharmonicity and large band degeneracy number, the metastable cubic SnSe exhibits promising thermoelectic (TE) performances theoretically and attracts extense attentions. Experimentally, ABX2 compounds alloying can effectively stabilize the cubic structure. However, newly emerging shortcomings like low carrier mobilitys and tiny band gaps hinder further optimizations of their TE properties. In this work, the carrier transport mechanism on the typical cubic Sn0.5-xPbx(AgSb)0.25Se sample is innovatively investigated, revealing that the pristine grain boundary scattering near room temperature changes to a mixed scattering of acoustic phonons and alloys due to the grain growth. Combined with the reduced effective mass by Pb doping, a significant improvement is realized in the mobility, leading to an increased power factor PF (∼7 W cm−1K−2) and a relatively high PFave (5.6 W cm−1K−2). What’s more, Pb doping also makes a big contribution in the reduction of thermal transports: on the one hand, enhancing the high-frequancy phonons scattering via strong mass fluctuation and stress flied fluctuation; on the other hand, enlarging the band gap by enhanced spin–orbit coupling effect, suppressing the bipolar diffusion at elevated temperatures. Resultantly, a small lattice and bipolar contributed thermal conductivity (κl + κbi) of 0.58 W m−1K−1 is obtained near 850 K in Sn0.38Pb0.12(AgSb)0.25Se sample, only 59 % of the pristine Sn0.5 (AgSb)0.25Se sample. Finally, an improved TE figure of merit zT value of 0.8 and a zTave value of 0.47 are obtained.

Robust superconductivity and huge enhancement of upper critical field in Nb2CS2 MXene under high pressure

As a member of the emerging MXenes family, Nb2CS2 offers distinctive superconductivity, excellent electrical properties, and outstanding chemical stability, making it potentially useful for energy storage, medical imaging, and quantum computing. Herein, we systematically investigate how ultrahigh pressure affects the electrical properties of Nb2CS2. The results indicate that Nb2CS2 retains robust superconductivity with Tc>8 K up to the maximum applied pressure of 146.8 GPa. Moreover, the upper critical magnetic field Hc2(0) of Nb2CS2 increases with pressure, and the Pauli limit is violated at pressures greater than 120 GPa. Meanwhile, Hc2(0) increases to 19.3 T at 146.8 GPa, which is 4.8 times greater than at the initial pressure. Further analysis suggests that the significant enhancement of Hc2(0) below 30 GPa comes from the sharp pressure-induced rise of carrier concentration as the interlayer distance decreases, and the significant increase in Hc2(0) above 86 GPa may come from enhanced spin–orbit coupling or the possible unconventional superconducting pairing mechanisms. These results provide insights into the superconducting properties of MXene materials and offer guidelines for further research on electronic transport in Mxenes under ultrahigh pressure.

Theoretical studies of new iridium-based terpolymer donors for high-efficiency triplet-material-based organic photovoltaics: Incorporation of different iridium(III) complexes

Screening potential terpolymer donors for high-performance triplet-material-based organic photovoltaics (T-OPVs) has been a challenge. Herein, four terpolymer donors, with different bis-tridentate iridium(III) complexes incorporated into the backbone of PTB7Ir, were designed and investigated by DFT and TD-DFT methods. The results show that, for designed 1–4 molecules, the bis-tridentate architecture in iridium complexes contributes to the formation of the orbital transitions involving iridium atoms, and promotes the enhancement of spin-orbit coupling (SOC) in heavy metals. Based on the efficient exciton transformation channel from the lowest singlet (S1) state to the third triplet (T3) state, the designed 1–3 have smaller energy differences (ΔES1−T3) and larger SOC matrix elements (⟨S1|HSOC|T3⟩) between S1 and T3, resulting in the faster intersystem crossing (ISC) and triplet exciton formation. Furthermore, 1–3/PC71BM heterojunctions with –ΔGCRT<−0.1 eV (–ΔGCRT refers to the driving force of triplet charge recombination) could exhibit suppressed triplet charge recombination (CRT) processes. The calculation results suggest that designed 1–3 systems can present enhanced inter-facial charge transfer and photovoltaic performance, and become promising candidates for iridium-based terpolymer donors in T-OPVs. This work will provide valuable guidance for the molecular design of T-OPV terpolymer donors.

ESIPT-induced spin-orbit coupling enhancement leads to tautomer fluorescence quenching of the 10-HHBF molecule.

We present novel insights into the interplay between excited state intramolecular proton transfer (ESIPT) and spin-orbit coupling (SOC) in the 10-hydroxy-11H-benzo[b]fluoren-11-one (10-HHBF) molecule, utilizing the time-dependent density functional theory approach and femtosecond transient absorption spectroscopy. Our discoveries entail a reassessment of the luminescence mechanism for 10-HHBF, characterizing it as an ESIPT fluorophore. Additionally, we demonstrate that the molecule undergoes intersystem crossing (ISC) following proton transfer, which quenches the fluorescence of the proton-transferred state, thus resulting in the absence of dual emission and a limited spectral range of fluorescence. Furthermore, our investigation reveals that 10-HHBF displays an SOC enhancement feature induced by ESIPT, which facilitates the ISC process. This trait serves as a barrier to the application of 10-HHBF in single-molecule white light emitters (SMWLEs). Our findings underscore the notable influence of the ESIPT-induced spin-orbit interaction enhancement on luminescent properties, which necessitates consideration in the design of SMWLEs.

Enhanced Spin–Orbit Coupling in a Correlated Metal

We investigate the correlation effects on spin-orbit coupling (SOC) in a two-orbital Hubbard model on a square lattice by applying the variational Monte Carlo method. We consider an effective SOC constant $\lambda_{\text{eff}}$ in the one-body part of the variational wave function and mainly discuss the cases of the electron number per site $n=1$, that is, quarter filling. We find that $\lambda_{\text{eff}}$ is proportional to the bare value $\lambda$ and depends on the electron-electron interactions through $(U'-J')$ in a relatively wide parameter range in the paramagnetic (PM) phase, where $U'$ is the interorbital Coulomb interaction and $J'$ is the pair hopping interaction. Increasing the electron-electron interactions in the PM phase leads to a transition to an effective one-band state, in which the upper band becomes empty due to the enhanced $\lambda_{\text{eff}}$. We also construct phase diagrams considering magnetic order. The carrier doping effect on $\lambda_{\text{eff}}$ is also investigated. We find that $\lambda_{\text{eff}}$ enhances in a strongly correlated region around the Mott transition point and it is necessary to include the correlation effects beyond the Hartree-Fock approximation to describe the enhanced SOC properly.

Structural materials with afterglow room temperature phosphorescence activated by lignin oxidation

Sustainable afterglow room temperature phosphorescence (RTP) materials, especially afterglow RTP structural materials, are crucial but remain difficult to achieve. Here, an oxidation strategy is developed to convert lignin to afterglow materials with a lifetime of ~ 408 ms. Specifically, lignin is oxidized to give aromatic chromophores and fatty acids using H2O2. The aromatic chromophores are locked by a fatty acid-based matrix by hydrogen bonds, triggering enhanced spin orbit coupling and long afterglow emission. More interestingly, motivated by this discovery, an auto fabrication line is built to convert wood (natural structural materials) to wood with afterglow RTP emission (RTP wood) via in situ oxidation of naturally-occurring lignin located in the wood cell walls to oxidized lignin (OL). The as-prepared RTP wood exhibits great potential for the construction of sustainable afterglow furniture. With this research we provide a new strategy to promote the sustainability of afterglow RTP materials and structural materials.

Enhanced spin–orbit coupling in an epsilon-near-zero material

Light can carry both spin and orbital angular momentum. While it is known that a nonparaxial circularly polarized beam couples the spin angular momentum to orbital angular momentum, this phenomenon does not hold upon collimation of the field. With the rising interest in epsilon-near-zero photonics, integral ingredients to this field are the beam-shaping capabilities of such a regime. In this work, it is experimentally shown that a permanent conversion of spin-to-orbital angular momentum arises naturally from an incident circularly polarized field on an isotropic interface due to the asymmetry in the Fresnel coefficients. More significantly, the conversion efficiency can be substantially enhanced in the presence of an epsilon-near-zero film due to the unique Fresnel properties exhibited in such a regime. It is further shown that the conversion efficiency scales with the nonparaxiality of the incident field. Our study showcases the intriguing phenomena resulting from the combination of concepts as old as Fresnel coefficients and modern materials such as epsilon-near-zero films.

Stereospecific redox-mediated clusterization reconstruction for constructing long-lived, color-tunable, and processable phosphorescence cellulose

Developing color-tunable organic persistent room-temperature phosphorescence (p-RTP) materials are important in diverse optoelectronic applications but challenging. Here, stereospecific redox strategy is used to trigger clusterization reconstruction of cellulose in terms of clusterization structure and environment, resulting in long-lived and color-tunable phosphorescence of redox products. Extra unsaturated CO of oxidized 2,3-dialdehyde cellulose (DAC) and 2,3-dicarboxylic acid cellulose (DCC) can provide n-π* transition for enhanced spin–orbit coupling (SOC), facilitating the generation of triplet excitons. DAC with slow emission decay shows unique time-dependent afterglow; DCC would form different aggregated state, leading to a higher-energy blue afterglow. Reduced DAC (RDAC) provides more rigid crystalline environment for suppressing nonradiative relaxation, resulting in a striking lifetime of 799 ms. Finally, due to the long-lived, multicolor, and aqueous processable features, they are successfully applied in phosphorescence ink, screen printing, anti-counterfeit, and information encryption. The presented work fundamentally elucidates the role of clusterization reconstruction in p-RTP materials design.

Kohler’s rule and anisotropic Berry-phase effect in nodal-line semimetal ZrSiSe

Nodal-line semimetals, ZrSiX (X = S, Se, Te), provide an ideal platform to investigate the tunable Fermi surfaces by replacing chalcogens. Here, we study the magnetoresistance at various magnetic fields and temperatures in ZrSiSe and find the obedience of Kohler’s law and sigmoidal-shaped field dependence, which are different to the behavior reported in ZrSiS. This difference is caused by compensated carriers and the non-negligible contribution from the trivial band in ZrSiSe. Furthermore, an anisotropic Berry-phase effect is observed and can be attributed to the enhanced spin–orbit coupling and the effect of a trivial band induced by Se replacement. Our findings provide further understanding for the topological states in nodal-line semimetal ZrSiX families and reveal the potential applications on magnetic sensors by manipulating the topological states.

Enhancement of spin-orbit coupling and magnetic scattering in hydrogenated graphene

Spin-orbit coupling (SOC) can provide essential tools to manipulate electron spins in two-dimensional materials like graphene, which is of great interest for both fundamental physics and spintronics application. In this paper, we report the low-field magnetotransport of in situ hydrogenated graphene where hydrogen atoms are attached to the graphene surface in continuous low temperature and vacuum environment. Transition from weak localization to weak antilocalization with increasing hydrogen adatom density is observed, indicating enhancing Bychkov-Rashba-type SOC in a mirror symmetry broken system. From the low-temperature saturation of phase breaking scattering rate, the existence of spin-flip scattering is identified, which corroborates the existence of magnetic moments in hydrogenated graphene.

Photoluminescence Properties of Copolyimides Containing Naphthalene Core and Analysis of Excitation Energy Transfer between the Dianhydride Moieties

The photoluminescence (PL) properties of semi-aromatic polyimide (PI) films and their model compounds (MCs) prepared from dianhydrides having a rigid naphthalene core were analyzed. The PMMA-dispersed MC and copolymerized PI (CoPI) films derived from 2,3,6,7-naphthalenetetracarboxylic dianhydride (NTDA) exhibited long-lived phosphorescence owing to the suppression of molecular motion by the rigidity of a naphthalene core. Additionally, the PMMA-dispersed MC and the CoPI films derived from 1,5-dibromo derivative of NTDA (DBrNT) exhibited room-temperature phosphorescence due to the enhancement of spin-orbit coupling by bromine atoms. The photophysical processes of the CoPI films prepared from NTDA/DBrNT and 4,4'-oxydiphtalic dianhydride (ODPA) in which the latter absorption band is located at a shorter wavelength than the former were analyzed. After UV irradiation, efficient excitation energy transfer occurs from the ODPA to NTDA/DBrNT moieties, and only the emission from the latter moieties was observed. These results demonstrate that the CoPI films derived from two dianhydrides absorbing different UV wavelengths can be used as spectral conversion films that convert a wide range of UV-light into longer wavelength visible light.

Acceleration of Reverse Intersystem Crossing using Different Types of Charge Transfer States.

There is a need to boost the rate constant of reverse intersystem crossing (kRISC ) in thermally activated delayed fluorescence (TADF) materials for applications to organic light-emitting diodes. Recently, energy level matching of the locally excited state (LE) and charge transfer state (CT) has been reported to enhance kRISC . In this study, we conceptually demonstrate that kRISC can be improved even between CT states without LE states, through the use of different types of CT states. On the basis of this concept, we design a new compound, named DMAC-bPmT, where two phenyl groups of a well-known TADF material DMAC-TRZ are substituted by pyrimidine groups. Theoretical calculations indicated that the energy levels of the different CT states of DMAC-bPmT are very close and enhanced spin orbit coupling may be expected between them. As predicted, DMAC-bPmT experimentally exhibited a kRISC three times as high as that of DMAC-TRZ.

Anomalous Hall effect in graphene coupled to a layered magnetic semiconductor

Graphene is favorable to realize topological nontrivial state by introducing spin-orbit coupling and exchange field through the proximity effect. The recent discovery of van der Waals magnets allows great proximitized modulation on graphene by building atomically clean heterostructures. Here, we realize anomalous Hall effect in graphene coupling with a layered magnetic material, ${\mathrm{Fe}}_{x}{\mathrm{Sn}}_{1\ensuremath{-}x}{\mathrm{S}}_{2}$. The anomalous Hall resistance and the carrier density show a nonmonotonous dependence on the back-gate voltage, indicating emergence of band-structure transformation. Furthermore, low-field quantum interference measurement shows the enhancement of spin-orbit coupling (SOC) in the heterostructure. Our findings confirm that graphene coupling to ${\mathrm{Fe}}_{x}{\mathrm{Sn}}_{1\ensuremath{-}x}{\mathrm{S}}_{2}$ is an ideal platform that is likely to introduce a strong exchange field and SOC simultaneously, which has outstanding potential in realizing topological nontrivial states and spintronics.

Enhanced Spin-Orbit Coupling in Heavy Metals via Molecular Coupling.

5d metals are used in electronics because of their high spin-orbit coupling (SOC) leading to efficient spin-electric conversion. When C60 is grown on a metal, the electronic structure is altered due to hybridization and charge transfer. In this work, we measure the spin Hall magnetoresistance for Pt/C60 and Ta/C60, finding that they are up to a factor of 6 higher than those for pristine metals, indicating a 20-60% increase in the spin Hall angle. At low fields of 1-30 mT, the presence of C60 increased the anisotropic magnetoresistance by up to 700%. Our measurements are supported by noncollinear density functional theory calculations, which predict a significant SOC enhancement by C60 that penetrates through the Pt layer, concomitant with trends in the magnetic moment of transport electrons acquired via SOC and symmetry breaking. The charge transfer and hybridization between the metal and C60 can be controlled by gating, so our results indicate the possibility of dynamically modifying the SOC of thin metals using molecular layers. This could be exploited in spin-transfer torque memories and pure spin current circuits.

Single Platinum Atom Doping to Silver Clusters Enables Near‐Infrared‐to‐Blue Photon Upconversion

AbstractPhoton upconversion (UC) from near‐infrared (NIR) to visible has been realized using singlet‐to‐triplet absorption of sensitizers, which are currently limited to osmium complexes and semiconductor nanocrystals. Motivated by the atomically precise tunability of electronic structure and photophysical properties of noble metal clusters, which often possess absorption bands that extend into the NIR region, we investigated MAg24(SR)18 (M=Ag, Pt; SR=2,4‐dimethylbenzenethiolate) clusters as a new NIR‐absorbing sensitizer for triplet–triplet annihilation UC. Combined with a blue light emitter, the NIR excitation (λex=785 nm) of Ag25(SR)18 results in no UC emission, while PtAg24(SR)18 exhibits strong UC emission. This enhancement is primarily due to a significant increase in the intersystem crossing quantum yield of the cluster associated with the spin–orbit coupling enhancement in the M@Ag12 core.

Single Platinum Atom Doping to Silver Clusters Enables Near-Infrared-to-Blue Photon Upconversion.

Photon upconversion (UC) from near-infrared (NIR) to visible has been realized using singlet-to-triplet absorption of sensitizers, which are currently limited to osmium complexes and semiconductor nanocrystals. Motivated by the atomically precise tunability of electronic structure and photophysical properties of noble metal clusters, which often possess absorption bands that extend into the NIR region, we investigated MAg24 (SR)18 (M=Ag, Pt; SR=2,4-dimethylbenzenethiolate) clusters as a new NIR-absorbing sensitizer for triplet-triplet annihilation UC. Combined with a blue light emitter, the NIR excitation (λex =785 nm) of Ag25 (SR)18 results in no UC emission, while PtAg24 (SR)18 exhibits strong UC emission. This enhancement is primarily due to a significant increase in the intersystem crossing quantum yield of the cluster associated with the spin-orbit coupling enhancement in the M@Ag12 core.

Structural and Magnetic Studies of ABO4-Type Ruthenium and Osmium Oxides.

Oxides of the form ABO4 with A = K, Rb, Cs and B = Ru and Os have been synthesized and characterized by diffraction and magnetic techniques. For A = K the oxides adopted the tetragonal (I41/a) scheelite structure. RbOsO4, which crystallizes as a scheelite at room temperature, underwent a continuous phase transition to I41/amd near 550 K. RbRuO4 and CsOsO4 were found to crystallize in the orthorhombic (Pnma) pseudoscheelite structure, and both displayed discontinuous phase transitions to I41/a at high temperatures. CsOsO4 was determined to undergo a phase transition to a P21/c structure below 140 K. CsRuO4 crystallizes with a baryte-type structure at room temperature. Upon heating CsRuO4 a first order phase transition to the scheelite structure in I41/a is observed at 400 K. A continuous phase transition is observed to P212121 below 140 K. DC magnetic susceptibility data is consistent with long-range antiferromagnetic ordering at low temperatures for all compounds except for CsOsO4, which is paramagnetic to 2 K. The effective magnetic moments are in agreement with the spin only values for an S = 1/2 quantum magnet. Effective magnetic moments calculated for Os compounds were lower than their Ru counterparts, reflective of an enhanced spin orbit coupling effect. A magnetic structure is proposed for RbRuO4 consisting of predominately antiferromagnetic (AFM) ordering along the 001 direction, with canting of spins in the 100 plane. A small ordered magnetic moment of 0.77 μB was determined.

Osmium sensitizer with enhanced spin–orbit coupling for panchromatic dye-sensitized solar cells

A new osmium complex, CYC-33O, with reinforced 1MLCT and 3MLCT transitions for panchromatic response beyond 1000 nm of the device.

Magnetotransport properties of compensated semimetal HfB2 with high-density light carriers

We present a detailed magnetotransport study on HfB2, a possible topological nodal-line semimetal. HfB2 exhibits field-induced resistivity upturn and plateau behaviors at low temperature and high field, accompanying rather large magnetoresistance. The analysis of the field dependence of Hall and longitudinal resistivity shows that there are two kinds of carriers (electrons and holes) with almost same carrier concentrations and rather high mobilities in HfB2. Above field-induced phenomena can be well explained by using the two-band model with compensation condition. Even the carrier concentration is significantly high (∼1.8 1021 cm−3) in HfB2, much larger than other known topological semimetals with discrete Dirac nodal points, the electron-type carriers still have relatively small effective masses. In contrast to ZrB2, the slightly increased effective mass in HfB2 manifests the effect of enhanced spin–orbit coupling due to the large atomic number of Hf.