Spin-orbit Coupling Research Articles

Photonic Spin Hall Effect of Nanoparticles: Fundamentals, Advances, and Applications

AbstractThe net angular momentum of light remains conserved during propagation. This conservation leads to a spin transport which becomes evident when light encounters a refractive index gradient, i.e., when it is reflected, refracted, or scattered. The phenomenon is so‐called as the spin‐orbit interaction (SOI) of light has paved the way to manipulate the light‐matter interaction at the nanoscale and has remained the core of many recent studies. Particularly, the photonic spin Hall effect (PSHE) of light which is the microscopic spin splitting into circular polarization has given rise to novel applications, for example, precision metrology. The PSHE is well explored at planar interfaces, however much less attention is given to it when the optical potential gradient is of higher dimensionality, i.e., for nanoparticles. In this review, the theoretical description of the PSHE as well as the SOI in the scattering of light from nanoparticles are covered. Recent advances and trends in the PSHE in nanoparticles are reviewed. The review is concluded with suggestions for some novel directions in the field of PSHE of nanoparticles.

Electrical magnetochiral anisotropy and quantum metric in chiral conductors

Abstract Electrical magnetochiral anisotropy (EMCA) refers to the chirality- and current-dependent non- linear magnetoresistance in chiral conductors and is commonly interpreted in a semiclassical picture. In this work, we reveal a quantum geometry origin of EMCA using a chiral rectangular lattice model that resembles a chiral organic conductor (DM-EDT-TTF)2ClO4 studied for EMCA recently and exhibits symmetry-protected Dirac bands similar to those of graphene. Compared to the semiclassi- cal term, we find that Dirac states contribute significantly to EMCA via the quantum metric when Fermi energy is close to the Dirac point. Besides, we discover that a topological insulator state can emerge once spin-orbit coupling (SOC) is added to our chiral model lattice. Our work paves a path toward understanding quantum geometry in the magnetotransport of chiral materials.

Systematic Investigation of Electronic States and Bond Properties of LnO, LnO+, LnS, and LnS+ (Ln = La-Lu) by Spin-Orbit Multiconfiguration Perturbation Theory.

The electronic structures of lanthanide monoxides (LnO/LnO+) and monosulfides (LnS/LnS+) for all lanthanide series elements (Ln = La-Lu) have been systematically analyzed with sophisticated quantum chemical calculations. The ground electronic configuration has been determined to be Ln 4fn6s1 or 4fn+1 for the neutral molecules and Ln 4fn for the cations. The low-lying energy states resulting from spin-orbit coupling and ligand field effects have been resolved using spin-orbit multiconfiguration quasi-degenerate second-order perturbation theory calculations. The ionization energies of LnO (5.20-7.06 eV) are about 0.3-2.2 eV lower than those of LnS (5.54-9.22 eV) due to the difference in the Ln 6s and 4f orbital energies from which an electron is removed during the ionization process. The bond dissociation energies (BDEs) have been computed by the state-averaged general multiconfigurational perturbation theory and the completely renormalized coupled-cluster [CR-CC(2,3)] methods. The BDEs are highly dependent on the lanthanide elements as several factors of the lanthanides affect the bond dissociation. The calculated bond lengths and energies agree well with available experimental values and are systematically predicted for the series of lanthanide monoxides and monosulfides where experimental values are not available. Furthermore, the LS terms of low-lying energy states and their corresponding bond properties have been clarified in detail to systematize the similarities and differences of the lanthanide compounds.

Photodissociation of the CH2Cl radical: A high-level abinitio study.

Photodissociation of the CH2Cl radical is investigated by using high-level multireference configuration interaction abinitio methods, including the spin-orbit coupling. All possible fragmentation pathways, namely, CH2Cl + hν → CH2 + Cl, HCCl + H, and CCl + H2, have been analyzed. The potential-energy curves of the ground and several excited electronic states along the corresponding dissociating bond distance of each pathway have been calculated. Inclusion of the spin-orbit couplings is found to be crucial because it strongly determines the shape of the curves of the different excited states and, therefore, their photodissociation dynamics behavior. Analysis of the potential curves indicates that the pathways producing CH2 + Cl and HCCl + H can occur through a fast direct dissociation mechanism, while the pathway leading to CCl + H2 involves much slower dissociation mechanisms such as internal conversion between electronic states, predissociation, or tunneling through exit barriers. The main implications are that the two faster channels are predicted to be dominant, while the slower pathway is expected to be very unlikely and rather irrelevant. Appreciable actinic fluxes of solar irradiation are available at stratospheric altitudes where ozone is abundant, in the wavelength range where absorption of the first low-lying excited states of CH2Cl has been observed experimentally. Our results show that in this excitation energy range, the above-mentioned two dominant dissociation pathways are open and then could contribute to stratospheric ozone depletion.

Effects of spin–orbit coupling on tunnel magneto-resistance in resonant-tunneling magnetic tunnel junctions

Effects of spin–orbit coupling on tunnel magneto-resistance in resonant-tunneling magnetic tunnel junctions

Interface engineering of van der Waals heterostructures towards energy-efficient quantum devices operating at high temperatures

Abstract Quantum devices, which rely on quantum mechanical effects for their operation, may offer advantages, such as reduced dimensions, increased speed, and energy efficiency, compared to conventional devices. However, quantum phenomena are typically observed only at cryogenic temperatures, which limits their practical applications. Two-dimensional materials and their van der Waals (vdW) heterostructures provide a promising platform for high-temperature quantum devices owing to their strong Coulomb interactions and/or spin-orbit coupling. In this review, we summarise recent research on emergent quantum phenomena in vdW heterostructures based on interlayer tunnelling and the coupling of charged particles and spins, including negative differential resistance, Josephson tunnelling, exciton condensation, and topological superconductivity. These are the underlying mechanisms of energy-efficient devices, including tunnel field-effect transistors, topological/superconducting transistors, and quantum computers. The natural homojunction within vdW layered materials offers clean interfaces and perfectly aligned structures for enhanced interlayer coupling. Twisted bilayers with small angles may also give rise to novel quantum effects. In addition, we highlight several proposed structures for achieving high-temperature Majorana zero modes, which are critical elements of topological quantum computing. This review is helpful for researchers working on interface engineering of vdW heterostructures towards energy-efficient quantum devices operating above the liquid nitrogen temperature.

Correlated physics, charge and magnetic orders in moiré Kagomé systems

Abstract Moiré systems have emerged as an ideal platform for exploring the interaction effects and correlated states. However, most of the experimental systems were based on either the triangular or honeycomb lattice. In this study, based on the self-consistent Hartree-Fock calculation, we investigate the phase diagram of the Kagomé lattice in a recently discovered system with two degenerate Γ valley orbitals and strong spin-orbit coupling. By focusing on the filling factors of 1/2, 1/3 and 2/3, we identified various symmetry-breaking states by adjusting the screening length and dielectric constant. At the half filling, we discovered that the spin-orbit coupling induced Dzyaloshinskii-Moriya interaction stabilized a classical magnetic sate with 120° ordering. Additionally, we observed a transition to a ferromagnetic state with out-of-plane ordering. In the case of 1/3 filling, the system is ferromagnetically ordered due to the lattice frustration. Furthermore, for 2/3 filling, the system exhibits a pinned droplet state and a 120° magnetic ordered state at weak and immediate coupling strengths, respectively. For strong coupling case, when dealing with non-integer filling, the system is always charged ordered with sublattice polarization. Our study serves as a starting point for exploring the effects of correlation in moiré Kagomé system.

Enhancing Reverse Intersystem Crossing with Extended Inverted Singlet–Triplet (X−INVEST) Systems

AbstractThe discovery of triangular‐shaped molecules displaying an inverted singlet–triplet (INVEST) energy gap between their lowest singlet (S1) and triplet (T1) states opened the way for a new strategy to increase the internal quantum efficiency (IQE) of organic light‐emitting diodes (OLEDs), enhancing the reverse intersystem crossing (RISC) thanks to a downhill process. However, the compounds showing a negative ΔEST suffer from both a vanishing spin–orbit coupling (SOC) between these excited states and high energy differences with higher‐lying singlets and triplets, therefore limiting their involvement in the spin conversion process. Here, we proposed a new design strategy entailing the extension of the triangulene cores by connecting two INVEST triangulene units to form Uthrene‐ and Zethrene‐like systems, doped with N and B. The inspection of the resulting molecular orbitals (MOs) distribution allowed rationalizing the electronic structure properties obtained from wavefunction‐based methods, showing how the Uthrene‐like architecture can lead to the quasi‐resonance between S1 and T1, in some cases provoking their inversion. By feeding a kinetic model with the non‐radiative rate constants, calculated from first principles, we showed how the extended INVEST (X−INVEST) design strategy can open new pathways to boost the spin conversion process and the population of the emissive S1.

Electronic and optical properties of a Ta2NiSe5 monolayer: A first-principles study

The crystal structure, stability, electronic, and optical properties of the Ta2NiSe5 monolayer have been investigated using first-principles calculations in combination with the Bethe–Salpeter equation. The results show that it is feasible to directly exfoliate a Ta2NiSe5 monolayer from the low-temperature monoclinic phase. The monolayer is stable and behaves as a normal narrow-gap semiconductor with neither spontaneous excitons nor non-trivial topology. Despite the quasi-particle and optical gaps of only 266 and 200 meV, respectively, its optically active exciton has a binding energy up to 66 meV and can exist at room temperature. This makes it valuable for applications in infrared photodetection, especially its inherent in-plane anisotropy adds to its value in polarization sensing. It is also found that the inclusion of spin–orbit coupling is theoretically necessary to properly elucidate the optical and excitonic properties of a monolayer.

Three-Dimensional Topological Semimetal/Insulator States in α-Type Organic Conductors with Interlayer Spin–Orbit Interaction

Three-Dimensional Topological Semimetal/Insulator States in <i>α</i>-Type Organic Conductors with Interlayer Spin–Orbit Interaction

Spin-Orbital Ordering Effects of Light Emission in Organic-Inorganic Hybrid Metal Halide Perovskites.

Organic-inorganic hybrid metal halide perovskites carrying strong spin-orbital coupling (SOC) have demonstrated remarkable light-emitting properties in spontaneous emission, amplified spontaneous emission (ASE), and circularly-polarized luminescence (CPL). Experimental studies have shown that SOC plays an important role in controlling the light-emitting properties in such hybrid perovskites. Here, the SOC consists of both orbital (L) and spin (S) momentum, leading to the formation of J (= L + S) excitons intrinsically involving orbital and spin momentum. In general, there are three issues in determining the effects of SOC on the light-emitting properties of J excitons. First, when the J excitons function as individual quasi-particles, the configurations of orbital and spin momentum directly decide the formation of bright and dark J excitons. Second, when the J excitons are mutually interacting as collective quasi-particles, the exciton-exciton interactions can occur through orbital and spin momentum. The exciton-exciton interactions through orbital and spin momentum give rise to different light-emitting properties, presenting SOC ordering effects. Third, the J excitons can develop ASE through coherent exciton-exciton interaction and CPL through exciton-helical ordering effect. This review article discusses the SOC effects in spontaneous emission, ASE, and CPL in organic-inorganic hybrid metal halide perovskites.

Side‐Gate Modulation of Supercurrent in InSb Nanoflag‐Based Josephson Junctions

InSb nanoflags, due to their intrinsic spin–orbit interactions, are an interesting platform in the study of planar Josephson junctions. Ballistic transport, combined with high transparency of the superconductor/semiconductor interfaces, is reported to lead to interesting phenomena such as the Josephson diode effect. The versatility offered by the planar geometry can be exploited to manipulate both carrier concentration and spin–orbit strength by electrical means. Herein, experimental results on InSb nanoflag‐based Josephson junctions fabricated with side gates placed in close proximity to the junction are presented. It is shown that side gates can efficiently modulate the current through the junction, both in the dissipative and in dissipation‐less regimes, similar to what is obtained with a conventional back gate. Furthermore, the side gates can be used to influence the Fraunhofer interference pattern induced by the presence of an external out‐of‐plane magnetic field.

Magnetic ground state and excitations in the mixed 3d−4d quasi-one-dimensional spin-chain oxide Sr3NiRhO6

Entanglement of spin and orbital degrees of freedom, via relativistic spin-orbit coupling, in 4d transition metal oxides can give rise to a variety of unique quantum phases. A previous study of mixed 3d−4d quasi-1D spin-chain oxide Sr3NiRhO6 using the magnetization measurements by Mohapatra [] revealed a partially disordered antiferromagnetic structure below 50 K. We here report the magnetic ground state and spin-wave excitations in Sr3NiRhO6 using muon spin rotation and relaxation (μSR), and neutron (elastic and inelastic) scattering techniques. Our neutron diffraction study reveals that in the magnetic structure of Sr3NiRhO6 Rh4+ and Ni2+ spins are aligned ferromagnetically in a spin chain, with moments along the crystallographic c axis. However, spin chains are coupled antiferromanetically in the ab plane. μSR reveals the presence of oscillations in the asymmetry-time spectra below 50 K, supporting the long-range magnetically ordered ground state. Our inelastic neutron scattering study reveals gapped quasi-1D magnetic excitations with a large ratio of gap to exchange interaction. The observed spin-wave spectrum could be well fitted with a ferromagnetic isotropic exchange model (with J=3.7 meV) and single ion anisotropy (D=10 meV) on the Ni2+ site. The magnetic excitations survive up to 85 K, well above the magnetic ordering temperature of ∼50 K, also indicating a quasi-1D nature of the magnetic interactions in Sr3NiRhO6. Published by the American Physical Society 2024

Tunnel magneto-resistance of double-barrier magnetic tunnel junctions with a central ferrimagnet layer including spin-orbit coupling

Tunnel magneto-resistance of double-barrier magnetic tunnel junctions with a central ferrimagnet layer including spin-orbit coupling

Floquet analysis on an irradiated nodal surface semimetal with non-symmorphic symmetry

A nodal surface semimetal (NSSM) features symmetry enforced band crossings along a surface within the three-dimensional (3D) Brillouin zone (BZ) and a presence of a nonsymmorphic symmetry there pushes such surfaces to stick to the BZ center or boundaries. The topological robustness of the same does not always come with nonzero Berry fluxes. We consider two such NS, one with zero and another with nonzero topological charges and investigate the effect of light irradiation on them. We find that depending on the state of polarization, one can obtain additional Weyl points/NS in the corresponding Floquet Hamiltonians. Particularly, using a simple two band spinless/spin polarized models with no spin orbit coupling, we emphasize the low energy behavior of the continuum Hamiltonians close to the band crossings and its evolution in a Floquet system in the high frequency limit. In the Floquet system, we also find the NS to perish or new multi Weyl points to get popped up for different polarization scenario or different NSSM Hamiltonians. Our findings open up important avenues on what out of equilibrium NSSM systems can offer in many active fields including quantum computations.

Pendant engineering in multiple-resonance thermally activated delayed fluorescence to yield charge-transfer and locally excited-state characteristics.

Multiple-resonance thermally activated delayed fluorescence (MR-TADF) materials can exhibit narrow-spectrum characteristics owing to the inhibition of rotation within the molecules. However, the excited states of these MR-TADF materials, which influence the spin-orbit couplings (SOCs) and device efficiencies of organic light-emitting diodes (OLEDs), have not been investigated to date. In this study, we synthesized MR-TADF materials tDABNA-TP, tDABNA-DN, and tDABNA-DOB by incorporating characteristic neutral, donor, and acceptor pendants into 2,12-di-tert-butyl-5,9-bis(4-(tert-butyl)phenyl)-5,9-dihydro-5,9-diaza-13b-boranaphtho[3,2,1-de]anthracene (tDABNA). To determine the effect of pendant engineering, we investigated the excited states of the MR-TADF materials, including their singlet and triplet excited states, calculated the SOCs for their optimal reverse intersystem crossing pathways, and determined their maximum external quantum efficiencies (EQEmax) in OLEDs. The OLED with the emitter bearing the neutral pendant (tDABNA-TP) exhibited the highest EQEmax of 20.7% among those with the emitters bearing the donor (16.6%) and acceptor (12.4%) pendants, with a narrow emission range of 472-492 nm. Furthermore, the device with the tDABNA-TP emitter exhibited an operating lifetime of 196 h, which was 1.42- and 1.92-fold longer than those of the devices with the tDABNA-DN and tDABNA-DOB emitters, respectively. Our findings will promote research on the pendant engineering of MR-TADF-based OLEDs.

Topological superconductivity in monolayer Td−MoTe2

Topological superconductivity has attracted significant attention due to its potential applications in quantum computation, but its experimental realization remains challenging. Recently, monolayer Td−MoTe2 was observed to exhibit gate tunable superconductivity, and its in-plane upper critical field exceeds the Pauli limit. Here, we show that an in-plane magnetic field beyond the Pauli limit can drive the superconducting monolayer Td−MoTe2 into a topological superconductor. The topological superconductivity arises from the interplay between the in-plane Zeeman coupling and the unique Ising plus in-plane spin-orbit coupling (SOC) in the monolayer Td−MoTe2. The Ising plus in-plane SOC plays the essential role to enable the effective px + ipy pairing. As the essential Ising plus in-plane SOC in the monolayer Td−MoTe2 is generated by an in-plane polar field, our proposal demonstrates that applying an in-plane magnetic field to a gate tunable 2D superconductor with an in-plane polar axis is a feasible way to realize topological superconductivity.

Examining Magnetic Properties and Multiferroicity in the Isostructural Cu2TSiS4 (T = Mn and Fe) System Based on the DFT Approach and the Orbital Interaction Analysis.

In the experiment, despite their structural and electronic similarities, Cu2MnSiS4 exhibits AFM ordering characterized by a propagation vector k = (1/2, 0, 1/2), while Cu2FeSiS4 has a different type of AFM ordering with a propagation vector k = (1/2, 1/2, 1/2). To unravel how these differences arise, we investigated magnetic properties of Cu2TSiS4 (T = Mn and Fe) based on the DFT calculation and an orbital interaction analysis. We suggest that the Cu+ ion plays an important role in exhibiting different magnetic structures for the isostructural and pseudoisoelectronic Cu2TSiS4 (T = Mn and Fe) compounds. In detail, participation of Cu+ ions into spin exchange interaction J5, which is a spin exchange interaction along the b-direction, is critical for exhibiting AFM coupling of J5, and the strength of this effect should be responsible for exhibiting different magnetic structures of Cu2MnSiS4 and Cu2FeSiS4. We also explored the ferroelectric polarization of the Cu2TSiS4 (T = Mn and Fe) system on the basis of DFT + U and DFT + U + SOC calculation. Our result reveals that the ferroelectric polarization of the Cu2TSiS4 (T = Mn and Fe) system is mainly governed by its geometric structure rather than its magnetic order and the spin-orbit coupling effect.

3d oxide molecules to tailor large magnetic anisotropy energies on MgO films

Designing systems with large magnetic anisotropy energy (MAE) is desirable and critical for nanoscale magnetic devices. A recent breakthrough achieved the theoretical limit of the MAE for 3d transition metal atoms by placing a single Co atom on a MgO(100) surface, a result not replicated by standard first-principles simulations. Our paper, incorporating Hubbard-U correction and spin-orbit coupling, successfully reproduces and explains the high MAE of a Co adatom on a MgO (001) surface. We go further by exploring ways to enhance MAE in 3d transition metal adatoms through different structural geometries of 3d−O molecules on MgO. One promising structure, with molecules perpendicular to the surface, enhances MAE while reducing substrate interaction, minimizing spin fluctuations, and boosting magnetic stability. Additionally, we demonstrate significant control over MAE by precisely placing 3d−O molecules on the substrate at the atomic level. Published by the American Physical Society 2024

Enhanced perpendicular magnetic anisotropy energy and Curie temperature in the CrOCl monolayer: strain effects

Abstract Magnetic monolayers offer a wide variety of applications in enhancing the functionalities of storage devices including higher thermal stability, lower power consumption, and higher operation speed, owing to their intrinsic long-range spin ordering. Herein, we study the biaxial ([110]) strain range of ± 5% influence on the formation energetics, electronic structure, and magnetic behaviour of the CrOCl monolayer (ML) based on the ab-initio calculations including spin–orbit coupling (SOC) effects. It is predicted that the system displays an insulating character having an energy band gap (E g ) of 2.05 eV with a ferromagnetic (FM) ground state in its unstrained state. The estimated partial spin magnetic moment on the Cr ion is +2.7 μ B /f.u. (per formula unit) with S = 1.5 and lies in a + 3 oxidation state with an electronic distribution of t 2 g 3 ↑ t 2 g 0 ↓ e g 0 ↑ e g 0 ↓ . Along with this, [001] (c-axis) is found to be the easy magnetic axis, which results in a magnetic anisotropy energy (MAE) of 0.2 meV having an MAE constant of 0.25 mJ m−2 and the computed Curie temperature (T c ) using Ising model is 157 K. Furthermore, the system shows the robustness of the FM insulating behavior against considered strains. However, a significant shift in the conduction band edge (CBE) position to lower energies is evident for tensile strains, which substantially reduces the E g up to 13%. The decrease in E g value is evidence of higher absorption in the visible range which makes it the best option for optoelectronics and photocatalysis. Simultaneously, our results revealed that strain enhances the MAE and T c up to 190% and 43%, respectively. Hence, optimized E g , MAE, and T c within a considerable strain range, make the CrOCl ML a potential candidate for its utilization in magnetic memory devices.