Spin Response Research Articles

Nonequilibrium two-particle self-consistent approach

We present the nonequilibrium implementation of the two-particle self-consistent (TPSC) approach, which has been shown to provide a reliable equilibrium description of interacting lattice systems in the weak- and intermediate-correlation regime. This method captures the effects of local and nonlocal correlations in two- and higher-dimensional systems and satisfies the Mermin-Wagner theorem. We demonstrate the versatility of nonequilibrium TPSC with calculations of the time-dependent spin and charge response functions and the evolution of effective temperatures extracted from different correlation functions, after interaction ramps in the two-dimensional Hubbard model.

Two-dimensional Hubbard model at finite temperature: Weak, strong, and long correlation regimes

We investigate the momentum-resolved spin and charge susceptibilities, as well as the chemical potential and double occupancy in the two-dimensional Hubbard model as functions of doping, temperature and interaction strength. Through these quantities, we identify a weak-coupling regime, a strong-coupling regime with short-range correlations and an intermediate-coupling regime with long magnetic correlation lengths. In the spin channel, we observe an additional crossover from commensurate to incommensurate correlations. In contrast, we find charge correlations to be only short ranged for all studied temperatures, which suggests that the spin and charge responses are decoupled. These findings were obtained by a novel connected determinant diagrammatic Monte Carlo algorithm for the computation of double expansions, which we introduce in this paper. This permits us to obtain numerically exact results at unprecedentedly low temperatures $T\geq 0.067$ for interactions up to $U\leq 8$, while working on arbitrarily large lattices. Our method also allows us to gain physical insights from investigating the analytic structure of perturbative series. We connect to previous work by studying smaller lattice geometries and report substantial finite-size effects.

Insight into the activation of persulfate with ZrO2 modified S-doped g-C3N4 nanocomposite for degradation of tetracycline hydrochloride

In this study, ZrO2 modified S-doped g-C3N4 (ZSCN) is synthesized as an innovative and efficient solar light-driven heterojunction nanocomposite. A sulfate radical based advanced oxidation process (SRAOP) coupled with as-prepared nanocomposite for solar degradation of tetracycline hydrochloride (TCH) is employed in the presence of persulfate ions (PS). The TCH degradation efficiency of the operational parameters comprising the initial TCH amount, pH, and photo-catalyst dosage on the TCH degradation process are investigated. The presence of the PS ions as an electron acceptor significantly enhanced the degradation of TCH under solar light irradiation. Surprisingly, the ZSCN + PS system exhibited excellent degradation of 93.4 % for the initial concentration (40 mg/L) of TCH solution within 150 min. Compared to pure ZSCN, the enhanced degradation efficiency results from higher solar light absorption and a larger surface area. Also, the heterojunction formation at the ZrO2/S-g-C3N4 interface effectively improves the electron-hole separation efficiency. Radical scavenging test and electron spin response (EPS) studies were used to identify the reactive oxygen species (ROS) generated in ZSCN + PS process. 1O2 was verified to be the major ROS responsible for TCH degradation. Scavenger tests and ESR analysis have shown that the •O2− as major radical, along with •OH and •SO4−, were essential free radicals that played a key part in the TCH degrading pathway. The re-usability and stability of heterojunction nanocomposite are evaluated through recycling experiments. It is supposed that the current work can provide a positive direction for the design and fabrication of various photo-catalysts for the treatment of water pollution effectively.

Bulk photospin effect: Calculation of electric spin susceptibility to second order in an electric field

We compute the electric spin susceptibility of Bloch electrons with spin-orbit coupling to second order. We find that it is possible to generate a nonequilibrium spin polarization in the bulk of non-magnetic inversion-symmetric materials using linearly polarized electric fields, but the process depends on interband coherence and produces heating. It may be possible to avoid heating with circular polarization in certain scenarios. The standard Edelstein effect and spin orientation effects are recovered in appropriate limits within the formalism. Finally, the electric spin susceptibility of metals has contributions proportional to spin multipole moments of the Fermi sea that dominate the low frequency spin response.

Charge-to-spin conversion in twisted graphene/WSe2 heterostructures

We investigate the twist angle dependence of spin-orbit coupling (SOC) proximity effects and charge-to-spin conversion (CSC) in graphene/WSe$_2$ heterostructures from first principles. The CSC is shown to strongly depend on the twist angle, with both the spin Hall and standard Rashba-Edelstein efficiencies optimized at or near 30{\deg} twisting. Symmetry breaking due to twisting also gives rise to an unconventional Rashba-Edelstein effect, with electrically generated non-equilibrium spin densities possessing spins collinear to the applied electric field. We further discuss how the carrier doping concentration and band broadening control the crossover between the Fermi-sea and -surface spin response, which reconciles the seemingly disparate experimental observations of different CSC phenomena.

Competing instabilities of the extended Hubbard model on the triangular lattice: Truncated-unity functional renormalization group and application to moiré materials

A simple yet paradigmatic model for the interplay of strong electronic correlations and geometric frustration is the triangular lattice Hubbard model. Recently it was proposed that moir\'e structures of transition metal dichalcogenides can be used to simulate extended versions that include non-local density-density interactions. We study competing instabilities of interacting electrons in such an extended Hubbard model on the triangular lattice near a filling where the density of states has a Van Hove singularity. We employ a truncated-unity functional renormalization group approach to investigate two cases: a paradigmatic minimally extended Hubbard model and a specific model with parameters that are applicable to hetero-bilayers of transition metal dichalcogenides. We unravel rich phase diagrams, including tendencies to spin-density-wave order and unconventional pairing, which can give rise to topological superconductivity. We classify the symmetry of the superconducting instabilities according to their irreducible representations and show that higher lattice harmonics are dominant when the nearest-neighbor interaction is sizable indicating pair formation between second-nearest neighbors. The phenomenological consequences can be enhanced spin and thermal quantum Hall responses in a topological superconductor.

Construction of Ag: ZnIn2S4/Bi2S3 Z-scheme heterojunctions for boosting interfacial charge separation and photocatalytic degradation of TC

The construction of Z-scheme heterostructures is one of the most effective strategies to improve photocatalytic efficiency. In this study, Ag+ doped ZnIn2S4/Bi2S3 composite nanosphere materials with different mass fractions of Bi2S3 were successfully synthesized by the solvothermal method. Systematic studies showed that the construction of heterogeneous structures and Ag+ doping could extend the optical absorption edge and provide more active sites. More importantly, it was shown by photoelectrochemical and PL spectroscopy tests that Ag: ZnIn2S4/Bi2S3 has strong visible light absorption and photocarrier transfer capability. In addition, the Z-scheme mechanism of Ag: ZnIn2S4/Bi2S3 was investigated by electron spin response (ESR) and active substance capture experiments, which confirmed that both superoxide radicals(O−2) and hydroxyl radicals(OH) were involved in the photocatalytic reaction. The results showed that the optimized Ag: ZnIn2S4/2.5%Bi2S3 degraded TC by 89.7%, 1.87 times higher than the original ZnIn2S4. This work provides a promising method for the construction of Z-scheme heterojunctions based on ZnIn2S4.

Novel scheme towards interfacial charge transfer between ZnIn2S4 and BiOBr for efficient photocatalytic removal of organics and chromium (VI) from water.

Construction of Z-scheme heterostructure is an effective strategy to enhance the charge carriers' separation. However, successfully achieving this on the defect heterojunction to improve the photocatalytic activity remains challenging. This work successfully obtained sulfur vacancy in the ZnIn2S4/BiOBr (SZIS/BOB) heterojunction composites with S-O covalent bonding using a hydrothermal method. As a result, they exhibited superior photocatalytic and stability performance. The optimized SZIS/BOB-10 exhibited excellent rhodamine B degradation (95.2%) and chromium (VI) reduction (97.8%) within 100min under visible light. The enhanced composites with S-vacancies, S-O bond, and internal electric field induced the Z-scheme charge transfer mechanism. We had verified this mechanism based on the surface photovoltage spectra, electron spin response spectra, and density functional theory calculations. This work not only provides valuable insights into designing photocatalysts with a direct Z scheme heterostructure but also delineates a promising strategy for developing efficient photocatalysts to degrade organic pollutants.

Intrinsic Nonlinear Electric Spin Generation in Centrosymmetric Magnets.

We propose an intrinsic nonlinear electric spin generation effect, which can dominate in centrosymmetric magnets. We reveal the band geometric origin of this effect and clarify its symmetry characters. Asan intrinsic effect, it is determined solely by the material's band structure and represents a material characteristic. Combining our theory with first-principle calculations, we predict sizable nonlinear spin generation in single-layer MnBi_{2}Te_{4}, which can be detected in experiment. Our theory opens a new route for all-electric controlled spintronics in centrosymmetric magnets which reside outside of the current paradigm based on linear spin response.

Heterogeneous electro-Fenton using three-dimension Fe-Co-Bi/kaolin particle electrodes for degradation of quinoline in wastewater.

Wastewater containing quinoline has become a common pollutant in water and soil environments, which poses a threat to human health due to its carcinogenicity, teratogenicity, and mutagenicity. Quinoline's stability and toxicity hinders its degradation by conventional physicochemical and biological methods. In this contribution, Fe-Co-Bi/kaolin particle electrodes were prepared for the efficient degradation of quinoline in wastewater, and characterized by using scanning electron microscope, X-ray diffraction, pyridine-IR, Brunauer-Emmett-Teller, X-ray photoelectron spectroscopy, and four-probe resistivity test. Parameters affecting the degradation efficiency were optimized to be the particle electrode dosage of 40g/L, pH 3.5, H2O2 addition of 67.6mmol/L, electrical conductivity of 12.7ms/cm, and voltage of 20V. The constructed three-dimensional catalytic particle electrode system (3D-CPE) achieved 92.1% removal rate of chemical oxygen demand (COD) under the optimal conditions. Hydroxyl radicals (•OH) generated in the 3D-CPE process were identified by radical scavenging tests and electron spin response analysis. To unravel the degradation mechanism, the intermediate products were identified by using high performance liquid chromatography-mass spectrometry. The degradation mechanism was discussed with the help of theoretical calculation.

Nonlocality of Electrically-Induced Spin Accumulation in Chiral Metals

Spin accumulation induced by an electric field in chiral electron system is investigated based on a linear response theory. It is shown that the spin response function has a spatially uniform component due to the chiral angular momentum generation effect, resulting in a nonlocal spin generation. The result suggests a scenario for nonlocal long-range spin transport in chiral metals reported experimentally recently.

Spin accumulation in the spin Nernst effect

The spin Nernst effect is a phenomenon in which the spin current flows perpendicular to a temperature gradient. Similar to the spin Hall effect, this phenomenon also causes spin accumulation at the boundaries. Here, we study the spin response to the gradient of the temperature gradient with the use of Green's functions. Our formalism predicts physically observable spin accumulation without the ambiguity regarding the definition of the spin current or the magnetization correction. We prove the generalized Mott relation between the electric and thermal responses assuming the presence of time-reversal symmetry and the absence of inelastic scattering. We also find that thermal spin accumulation vanishes for the three-dimensional Luttinger model but is nonzero for the two-dimensional Rashba model with $\ensuremath{\delta}$-function nonmagnetic disorder in the first Born approximation.

Hydrothermal construction of flower-like g-C3N4/NiZnAl-LDH S-scheme heterojunction with oxygen vacancies for enhanced visible-light triggered photocatalytic performance

Construction of S-scheme heterojunction with high photocatalytic performance has been regarded as a promising way to treat organic wastewater thoroughly. In the present work, a novel S-scheme heterojunction with oxygen vacancies was successfully constructed between graphitic-carbon nitride(g-C3N4) nanosheets and NiZnAl layered double hydroxide (NiZnAl-LDH) by hydrothermal method. The as-synthesized g-C3N4/NiZnAl-LDH heterojunction displayed superior photocatalytic degradation activity over methyl orange (MO) and tetracycline (TC) aqueous solution compared with the pristine g-C3N4 and NiZnAl-LDH. Dramatically, the sample g-C3N4/NiZnAl-LDH (23%) exhibited the best photocatalytic activity, the photodegradation rate constants are 3.5, 12.7 times and 3.2, 5.5 times to pristine g-C3N4 and NiZnAl-LDH, respectively for the degradation of MO and TC. The enhanced photocatalytic activity is mainly due to the formation of S-scheme heterojunction modified by oxygen vacancy. In addition, a reasonable photocatalytic mechanism was proposed based on the photoluminescence (PL), electrochemical impedance (EIS), transient photocurrent test, active species capture and electron spin response (ESR/EPR) experiments combined with high performance liquid chromatography-mass spectrometry (HPLC-MAS) and total organic carbon (TOC) analysis. This work affords a new approach for the construction of efficient, stable and potential applications of g-C3N4 based S-scheme heterojunction photocatalysts.

Ising and XY paramagnons in two-dimensional 2H−NbSe2

Paramagnons are the collective modes that govern the spin response of nearly magnetic conductors. In some cases they mediate electron pairing leading to superconductivity. This scenario may occur in 2H-NbSe$_2$ monolayers, that feature spin-valley coupling on account of spin-orbit interactions and their lack of inversion symmetry. Here we explore spin anisotropy of paramagnons both for non-centrosymmetric Kane-Mele-Hubbard models for 2H-NbSe$_2$ monolayers described with a DFT-derived tight-binding model. In the infinite wavelength limit we find spatially uniform paramagnons with energies around $1$~meV that feature a colossal off-plane uniaxial magnetic anisotropy, with quenched transversal spin response. At finite wave vectors, longitudinal and transverse channels reverse roles: XY fluctuations dominate within a significant portion of the Brillouin zone. Our results show that 2H-NbSe$_2$ is close to a Coulomb-driven in-plane (XY) spin density wave instability.

Electrically detected electron nuclear double resonance in amorphous hydrogenated boron thin films

We report on electrically detected electron nuclear double resonance (EDENDOR) observations via spin dependent trap assisted tunneling (SDTAT) in amorphous boron thin films at 250 K. We observe EDENDOR from both 10B and 11B nuclei, likely interacting with carbon impurities. In SDTAT, electron paramagnetic resonance (EPR) is detected through a change in the trap assisted tunneling current through the thin film. As in conventional electron nuclear double resonance (ENDOR) the ENDOR response is detected through a modest change in the EPR response. Since SDTAT detection sensitivity is about seven orders of magnitude greater than that of conventional EPR, it, in principle, can provide an enormous boost in ENDOR sensitivity. This enormous potential sensitivity improvement can be compromised by a coupling of the RF electromagnetic field driving the nuclear spin response and the electrical leads which are utilized to monitor the resonance induced changes in device current. We overcome this difficulty with the introduction of proportional-integral-derivative (PID) control of the RF circuitry which greatly suppresses fluctuations in the amplitude of the RF magnetic field at the thin film structure under investigation.

Quantum Simulation of the Two-Dimensional Weyl Equation in a Magnetic Field.

Quantum simulation of 1D relativistic quantum mechanics has been achieved in well-controlled systems like trapped ions, but properties like spin dynamics and response to external magnetic fields that appear only in higher dimensions remain unexplored. Here we simulate the dynamics of a 2D Weyl particle. We show the linear dispersion relation of the free particle and the discrete Landau levels in a magnetic field, and we explicitly measure the spatial and spin dynamics from which the conservation of helicity and properties of antiparticles can be verified. Our work extends the application of an ion trap quantum simulator in particle physics with the additional spatial and spin degrees of freedom.

C-dots decorated SrTiO3/NH4V4O10 Z-scheme heterojunction for sustainable antibiotics removal: Reaction kinetics, DFT calculation and mechanism insight

Herein, we present an unprecedented feasible strategy for the removal of antibiotic residues in aqueous environments. A ternary C-dots/SrTiO3/NH4V4O10 catalyst was constructed by anchoring C-dots on the STO/NVO Z-scheme heterojunction by hydrothermal treatment. The synthesized catalyst was used for the degradation of sulfamethoxazole (SMX), aureomycin hydrochloride (CTC·HCl), and ciprofloxacin (CIP) under simulated solar light with the removal efficiencies of 94.7%, 88.3%, and 86.05% respectively, without significant inactivation even after four recycling experiments. Moreover, it shows application potential due to its superior removal efficiency towards the mixed antibiotics solution. The construction of Z-scheme heterojunction that exhibit good redox capacity and efficient charge transfer as well as the introduction of C-dots have a synergistic effect on the separation and migration of photogenerated carriers. Furthermore, the special 2D layered NH4V4O10 nanosheets are favoring for the pre-adsorption of antibiotics molecules and provide more reaction sites. HPLC-MS, electron spin response (ESR), and density functional theory (DFT) calculations enabled the elucidation of the photocatalytic mechanism and possible degradation pathways. This study will provide a reference for designing efficient C-dots mediated Z-scheme heterojunctions to remediate broad-spectrum antibiotic residues.

Spin accumulation without spin current

The spin Hall (SH) effect is a phenomenon in which the spin current flows perpendicular to an applied electric field and causes the spin accumulation at the boundaries. However, in the presence of spin-orbit couplings, the spin current is not well defined. Here, we calculate the spin response to an electric field gradient, which naturally appears at the boundaries. We derive a generic formula using the Bloch wave functions and the phenomenological relaxation time. We also calculate the response for the Rashba model with $\delta$-function nonmagnetic disorder within the first-order Born approximation and corresponding vertex corrections. We find the nonzero spin accumulation, although the SH conductivity exactly vanishes.

Synergistic Effect of Chiral Nanofibers Amplifying the Orbit Angular Momentum To Enhance Optomagnetic Coupling.

Manipulating magnetic bits by photon in spintronics, opto-magnetic coupling, is lagging far behind what we could expect. To investigate the issue, one should face the problem to find photon dependence of spin dynamics and spin manipulation. In this work, through introducing chiral orbit in organic crystals, circularly polarized photon can manipulate spin via the channel of photon-orbit-spin interactions. Under the stimulus of the magnetic field, strong spin polarization will feed back to the change in polarized state of light. Moreover, twisting several chiral nanofibers into a thick one, a more pronounced opto-magnetic coupling is clearly observed due to the chirality generated larger chiral orbit. Meanwhile, spin dynamics (or spin response times) inside the aggregated thick chiral fiber can be further tuned by circularly polarized light. Hopefully, this study can deepen the understanding of organic chiral spin-photonics and enhance the application of organic functional crystals in the future.

Novel Z-scheme In2S3/Bi2WO6 core-shell heterojunctions with synergistic enhanced photocatalytic degradation of tetracycline hydrochloride

Semiconductor photocatalytic technology is an effective strategy to cope with the current environmental issues. Therefore, the development of low-cost and environment-friendly catalysts with high efficacy has become a research focus and emphasis. Herein, novel Z-scheme In2S3/Bi2WO6 core-shell structure composites were controllably prepared by template and hydrothermal route. Highly improved photocatalytic degradation of tetracycline hydrochloride (TCH) over In2S3/Bi2WO6 core-shell composites was observed under visible-light (VL) irradiation (∼96.0%), which was 2.4 and 2.1 folds higher than that of In2S3 and Bi2WO6, respectively. The excellent oxygen activation and catalytic performance was ascribed to the synergistic effects of built-in electric field to ensure easy charge exchange at the interface of In2S3 and Bi2WO6, Z-scheme charge transfer path and the extended range of VL absorption. Superoxide radical (·O- 2) and hydroxyl (·OH) radicals were verified to be involved in the photocatalytic reaction by the active species capture experiment and the electron spin response (ESR) detection. The recycling experiments demonstrate the excellent stability and reusability of the In2S3/Bi2WO6. In addition, in accordance with the experimental results, the highly efficient Z-scheme photocatalytic mechanism and degradation paths were proposed. This work provided a new way for preparation of Z-scheme core-shell composites which had broad applications prospect in environmental remediation.