Spin Exchange Interaction Research Articles

Spatiotemporal characteristics of spin transport in compensated metals with electron–hole exchange interaction

We develop a theory describing spatiotemporal behavior of spin transport in two-band metals by postulating a spin–exchange interaction between electrons and holes. Starting with the semiclassical Boltzmann equation, we derive a system of coupled diffusion equations and solve them analytically under steady-state conditions. The solutions reveal two types of electron–hole coupled-spin transport modes: a dissipative mode and a nondissipative mode with an infinite spin diffusion length. The two modes are the manifestations of two types of spin coupling channels. Besides the exchange interaction, we incorporate into our derivation the relaxation caused by the spin–orbit interaction to show how it affects the spin transport characteristics of the two modes.

Spinning Molecules, Spinning Spins: Modulation of an Electron Spin Exchange Interaction in a Highly Anisotropic Hyperfine Field.

An investigation of spin and conformational dynamics in a series of symmetric Cu–Cu porphyrin dimer solutions is presented using electron paramagnetic resonance (EPR) spectroscopy. Previous spectral simulations focused on the isotropic exchange interaction (Javg) between the Cu centers. In this work, an additional line broadening parameter (Jmod) is explored in detail via variable temperature X-band EPR in liquid solution for several different structures. The Jmod phenomenon is due to fluctuations in the spin exchange interaction caused by conformational motion of the porphyrin planes. The Jmod parameter scales with the inverse of the rotational barriers that determine the Boltzmann-weighted torsional angle distribution between neighboring porphyrin planes. Arrhenius plots allow for extraction of the activation energies for rotation, which are 5.77, 2.84, and 5.31 kJ/mol for ethyne-bridged (porphinato)copper(II)-(porphinato)copper(II), butadiyne-bridged (porphinato)copper(II)-(porphinato)copper(II), and ethyne-bridged (porphinato)copper(II)-(porphinato)zinc(II)-(porphinato)copper(II) complexes, respectively. DFT calculations of these torsional barriers match well with the experimental results. This is the first report of a Jmod analysis within a highly anisotropic hyperfine field and demonstrates the utility of the theory for extraction of dynamic information.

Tunable magnetic coupling and high Curie temperature of two–dimensional PtBr3via van der waals heterostructures

Two-dimensional ferromagnetic semiconductors hold great promise for next-generation spintronic applications. However, candidates with high Curie temperature (Tc) are still lacking. Using the first-principles calculations, the PtBr3 monolayer is found to exhibit ferromagnetic order above the room temperature. The formation of PtBr3/WSe2 van der Waals heterostructures can increase the Tc to ∼ 410 K by additional super-exchange path of Pt-Se-Pt. The spin-exchange interactions for this path is as strong as ∼ 22 meV, which is superior to most other magnetic system. The out-of-plane compression further boosts the Tc to ∼ 636 K. The interlayer magnetic coupling is highly tunable depending on the stacking alignment, which closes or weakens some super-exchange channels. In addition, the interlayer interaction leads to a phase transition from half-metal to semiconductor, which greatly promotes its potential in spintronic applications. The strong stacking dependent feature is feasible to manipulate the magnetic orders by external strain or mechanical motion.

Monte Carlo simulation of a model cuprate

We develop a classical Monte Carlo algorithm based on a quasi-classical approximation for a pseudospin S = 1 Hamiltonian in real space to construct a phase diagram of a model cuprate with a high Tc. A model description takes into account both local and nonlocal correlations, Heisenberg spin-exchange interaction, correlated single-particle, and two-particle transport. We formulate a state selection algorithm for a given parameterization of the wave function in order to ensure a uniform distribution of states in the phase space. The simulation results show a qualitative agreement with the experimental phase diagrams.

Magnetic properties of ferromagnetic thin films with three spin layers as described by fourth-order perturbed Heisenberg Hamiltonian

The magnetic properties of ferromagnetic thin films with three spin layers were investigated for the first time using fourth-order perturbed Heisenberg Hamiltonian. Total magnetic energy was determined for ferromagnetic materials with simple cubic lattice. The simulation was carried out for Heisenberg Hamiltonian with different second-order magnetic anisotropy constants in different spin layers. The total magnetic energy periodically varies with spin-exchange interaction, azimuthal angle of spin, and the second-order magnetic anisotropy constant in each spin layer. The peaks along the axis of the angle are closely packed except in the 3-D plot of energy versus angle and second-order magnetic anisotropy constant of the middle spin layer. 2-D plots were perceived by rotating 3-D plots in MATLAB. According to the 3-D plot, the angle between magnetic easy and hard directions is 90 degrees. The minimum energy range was found in the 3-D plot of energy versus angle and the second-order anisotropy constant of the middle spin layer. The samples with the minimum magnetic anisotropy energies have potential application in transformer cores, magnetic switching, and magnetic amplifiers.

Evidence for new enantiospecific interaction force in chiral biomolecules

Evidence for new enantiospecific interaction force in chiral biomolecules

Influence of the Electric Charge of Spin Probes on Their Diffusion in Room-Temperature Ionic Liquids.

The rotational and translational diffusion of negatively charged and uncharged spin probes in five imidazolium-based room-temperature ionic liquids (RTILs), 1-ethyl-3-methylimidazolium tetrafluoroborate, emimBF4, 1-butyl-3-methylimidazolium tetrafluoroborate, bmimBF4, 1-octyl-3-methylimidazolium tetrafluoroborate, omimBF4, 1-octyl-3-methylimidazolium hexafluorophosphate, omimPF6, and 1-octyl-3-methylimidazolium chloride, omimCl, has been studied by means of electron paramagnetic resonance spectroscopy. Detailed analyses of the spin-Hamiltonian parameters and spin exchange interactions have been carried out. The temperature dependences of the line broadening induced by the electronic dipole-dipole interaction and the electron spin exchange coupling are determined. The translational mobility of spin probes is semiquantitatively characterized and successfully explained in the framework of a hypothesis based on the assumption of polar and unpolar domains within the RTILs.

The electronic and magnetic properties of KPbM2(PO4)3 (M = Cr and Fe) by first-principles calculations

The electronic and magnetic properties of two langbeinite-type phosphates KPbM2(PO4)3 (M = Cr and Fe) are studied by the first-principles calculations. It is found that both of them are anti-ferromagnetic semiconductors, in which the spin-exchange interactions between two M ions can be explained by the super-superexchange through the paths of M–O···O–M. The calculated spin moments and Curie–Weiss temperatures of the two materials agree well with the experimental results. Our work clarified the magnetic nature of KPbM2(PO4)3 and laid a good foundation for their possible applications in magnetic and other fields.

Theoretical Investigation in Coherent Manipulation throughout the Calculation of the Local Density of States in FM-DQD-FM Device

In this work, theoretical investigation in coherent manipulation throughout local density of states calculation for serially coupled double quantum dots embedded between ferromagnetic leads (FM-QD1-QD2-FM) by using the non-equilibrium Green's function approach. Since the local density of states are formulated incorporating the spin polarization and the type of spin configuration on the leads. Our model incorporates the inter-dot hopping, the intra-dot Coulomb correlation, the spin exchange energy and the coupling interactions between the quantum dots and leads. The results concerned to the parallel configuration at strong inter-dot coupling regime shows that the spin down electrons in the quantum dots may be more coupled coherently if the regime is tuned. The local density of states of the two dots for spin up electrons shows a broad hump with small splitting i.e. the case is decoherent for spin up electrons. In the case of weak interdot coupling it is obvious that the spin dependent density of states on the quantum dots show that the resonances are not well splitted. For the antiparallel configuration in the strong coupling regime, the spin dependent density of states of the double quantum dots show four peaks but with broaden and overlapping. In the case of weak coupling regime, the total spin dependent density of states, which have two peaks with certain board, one can conclude that the states are not coupled coherently. The case of the antiferromagnetic nature of the spin exchange interaction, our calculations for the parallel and antiparallel configurations (in strong and weak regimes) show a decoherence state.

Asymmetric conductivity of the Kondo effect in cold atomic systems

Motivated by recent theoretical and experimental advances in quantum simulations using alkaline earth (AE) atoms, we put forward a proposal to detect the Kondo physics in a cold atomic system. It has been demonstrated that the intrinsic spin-exchange interaction in AE atoms can be significantly enhanced near a confinement-induced resonance (CIR), which facilitates the simulation of Kondo physics. Since the Kondo effect appears only for antiferromagnetic coupling, we find that the conductivity of such system exhibits an asymmetry across a resonance of spin-exchange interaction. The asymmetric conductivity can serve as the smoking gun evidence for Kondo physics in the cold atom context. When an extra magnetic field ramps up, the spin-exchange process near Fermi surface is suppressed by Zee-man energy and the conductivity becomes more and more symmetric. Our results can be verified in the current experimental setup.

Ferromagnetism above Room Temperature in a Ni-Doped Organic-Based Magnetic Semiconductor.

Ferromagnetic semiconductors with structural flexibility are an indispensable feature for future flexible spin-electronic applications. In this case, we introduce magnetic ingredients into an organic semiconductor, namely, pentacene, to form a ferromagnetic organic semiconductor (FOS). The first observation for ferromagnetic Ni-doped pentacene semiconductors at room temperature in the field of semiconductor spintronics is reported in this article. To date, the mechanism of FOSs with ferromagnetism is not understood yet, especially when their Curie temperature is enhanced above room temperature. Here, we demonstrate dopants of Ni atoms and the modulation of the growth temperature in the FOS films to achieve room-temperature ferromagnetic properties in a series of FOS films, one of which has a maximum coercivity of 257.6 Oe. The spin-exchange interaction between a Ni atom and a pentacene molecule is detected through the magnetic hysteresis obtained using a superconducting quantum interference device magnetometer. We verify the effectiveness of this spin coupling through magnetic force microscopy, Raman spectroscopy, scanning Kelvin probe microscopy, and theoretical simulation. A model for the indirect spin coupling between Ni atoms is proposed for the mechanism of room-temperature ferromagnetic ordering of spins due to the exchange force indirectly. We believe that the π-electrons of pentacene molecules at the triple state for this model can support the spin coupling of electrons of Ni atoms. Our findings facilitate the development of brand-new spintronic devices with structural flexibility and room-temperature ferromagnetism.

Magnetism of Atomically Precise Gold and Doped Nanoclusters: Delocalized Spin and Interparticle Coupling

The magnetic properties of Au nanoparticles (NPs) have long been an intriguing topic in fundamental research. In the quantum size regime (1–3 nm), Au NPs indeed exhibit distinct magnetism in contrast to diamagnetic gold in bulk or relatively large plasmonic NPs. However, previous studies often give controversial results due to imprecise NPs used in magnetic studies, making it difficult to understand the origin of magnetism in Au NPs. Recent progress has led to atomically precise Au nanoclusters (NCs for differentiation with regular NPs), which can serve as a unique model for studying the delocalized spin in isolated NCs and the spin–spin exchange interaction between NCs in assembled solids. Moreover, such mechanisms are correlated to the atomic structures of the magnetic NCs. The precise formulas of the NCs serve as a clear indicator for magnetism. So far, the Au-thiolate NCs reported to be magnetic, including the doped ones, all contain icosahedral kernel structures, which are facile compared to other structures in adding or removing one electron for endowing magnetism to the NCs. Heteroatom doping in the NCs is an effective method to probe the magnetic mechanism in NCs, such as the origin of magnetic anisotropy, and the counterion tailoring for those charged NCs can also impart magnetism to the initially diamagnetic NCs via stabilizing a particular charge state of the NCs. While only a few cases of NCs have been reported with magnetism thus far, future research on metal NCs (especially in the critical regime between molecular and metallic state) will reveal more fundamentals of magnetism, and the control of spin–spin exchange coupling in nanocluster-assembled solids is particularly promising for tailoring the magnetic functionality of NCs and ultimately finding versatile applications.

Spinor F = 1 Bose-Einstein condensates loaded in two types of radially-periodic potentials with spin-orbit coupling* *Project supported by the National Natural Science of China (Grant Nos. 11904242 and 12004264) and the Natural Science Foundation of Hebei Province, China (Grant Nos. A2019210280 and A2019210124).

We consider two-dimensional spinor F = 1 Bose–Einstein condensates in two types of radially-periodic potentials with spin–orbit coupling, i.e., spin-independent and spin-dependent radially-periodic potentials. For the Bose–Einstein condensates in a spin-independent radially-periodic potential, the density of each component exhibits the periodic density modulation along the azimuthal direction, which realizes the necklacelike state in the ferromagnetic Bose–Einstein condensates. As the spin-exchange interaction increases, the necklacelike state gradually transition to the plane wave phase for the antiferromagnetic Bose–Einstein condensates with larger spin–orbit coupling. The competition of the spin-dependent radially-periodic potential, spin–orbit coupling, and spin-exchange interaction gives rise to the exotic ground-state phases when the Bose–Einstein condensates in a spin-dependent radially-periodic potential.

Realization of a bosonic antiferromagnet

Quantum antiferromagnets are of broad interest in condensed matter physics as they provide a platform for studying exotic many-body states including spin liquids and high-temperature superconductors. Here, we report on the creation of a one-dimensional Heisenberg antiferromagnet with ultracold bosons. In a two-component Bose-Hubbard system, we switch the sign of the spin-exchange interaction and realize the isotropic antiferromagnetic Heisenberg model in an extended 70-site chain. Starting from a low-entropy N\'eel-ordered state, we use optimized adiabatic passage to approach the bosonic antiferromagnet. We demonstrate the establishment of antiferromagnetism by probing the evolution of the staggered magnetization and spin correlations of the system. Compared with condensed matter systems, ultracold gases in optical lattices can be microscopically engineered and measured, offering significant advantages for exploring bosonic magnetism and spin dynamics.

Measuring spin-polarized electronic states of quantum materials: 2H−NbSe2

Probing the energy and spin electron properties of materials by means of photoemission spectroscopy gives insights into the low-energy phenomena of matter driven by spin orbit coupling or exchange interaction. The information that can be derived from complete photoelectron spectroscopy experiments, beyond $E$(k), is contained in the photoemission transition matrix elements that determine peak intensities. We present here a complete photoemission study of the spin-polarized bands of $2H\text{\ensuremath{-}}{\mathrm{NbSe}}_{2}$, a material that presents a surface spin-texture. Circular dichroism in angular-resolved photoemission spectroscopy (CD-ARPES) data are compared with spin-polarized angular-resolved spectra (SARPES) as measured with linearly polarized radiation in a well-characterized experimental chirality, at selected photon energy values. CD-ARPES is due to a matrix element effect that depends strongly on photon energy and experimental geometry: we show that it cannot be used to infer intrinsic spin properties in $2H\text{\ensuremath{-}}{\mathrm{NbSe}}_{2}$. On the other hand, SARPES data provide reliable direct information on the spin properties of the electron states. The results on $2H\text{\ensuremath{-}}{\mathrm{NbSe}}_{2}$ are discussed, and general methodological conclusions are drawn on the best experimental approach to the determination of the spin texture of quantum materials.

Room-Temperature Magnetic Field Effect on Excitonic Photoluminescence in Perovskite Nanocrystals.

Magnetic-field-enhanced spin-polarized electronic/optical properties in semiconductors are crucial for fabricating various spintronic devices. However, this spin polarization is governed by weak spin exchange interactions and easily randomized by thermal fluctuations; therefore, it is only produced at cryogenic temperatures, which severely limits the applications. Herein, a room-temperature intrinsic magnetic field effect (MFE) on excitonic photoluminescence is achieved in CsPbX3 :Mn (X = Cl, Br) perovskite nanocrystals. Through moderate Mn doping, the MFE is enhanced by exciton-Mn interactions, and through partial Br substitution, the MFE is stabilized at room temperature by exciton orbital ordering. The orbital ordering significantly enhances the g-factor difference between electrons and holes, which is evidenced by a parallel orbit-orbit interaction among excitons generated by circular polarized laser excitation. This study provides a clear avenue for engineering spintronic materials based on orbital interactions in perovskites.

Temperature Dependence of Charge and Spin Transfer in Azurin.

The steady-state charge and spin transfer yields were measured for three different Ru-modified azurin derivatives in protein films on silver electrodes. While the charge-transfer yields exhibit weak temperature dependences, consistent with operation of a near activation-less mechanism, the spin selectivity of the electron transfer improves as temperature increases. This enhancement of spin selectivity with temperature is explained by a vibrationally induced spin exchange interaction between the Cu(II) and its chiral ligands. These results indicate that distinct mechanisms control charge and spin transfer within proteins. As with electron charge transfer, proteins deliver polarized electron spins with a yield that depends on the protein’s structure. This finding suggests a new role for protein structure in biochemical redox processes.

Observation of spin-exchange dynamics between itinerant and localized Yb171 atoms

We report on the observation of the spin-exchange dynamics of $^{171}\mathrm{Yb}$ atoms in the ground state $^1\mathrm{S}_0$ and in the metastable state $^3\mathrm{P}_0$. We implement the mixed-dimensional two-orbital system using a near-resonant and magic-wavelength optical lattices, where the $^1\mathrm{S}_0$ and $^3\mathrm{P}_0$ atoms are itinerant in a one-dimensional tube and localized in three dimensions, respectively. By exploiting an optical Stern-Gerlach method, we observe the spin depolarization of the $^1\mathrm{S}_0$ atoms induced by the spin-exchange interaction with the $^3\mathrm{P}_0$ atom. Our work could open the way to the quantum simulation of the Kondo effect.

Superconductivity with and without glue and the role of the double-occupancy forbidding constraint in the t−J−V model

The occurrence of retarded (with glue) and unretarded (without glue) pairing is thoroughly discussed in cuprates. We analyze some aspects of this problem in the context of the t-J-V model in a large-N approximation. When 1/N renormalizations are neglected the mean-field result is recovered, where the unretarded d-wave superconducting pairing triggered by the spin-exchange interaction J is obtained. However, the presence of a non-negligible nearest-neighbors Coulomb interaction V(q) kills superconductivity. If the non-double-occupancy constraint and its fluctuations are considered, the situation changes drastically. In this case, V(q) is screened making d-wave superconductivity very robust. In addition, we show that the early proposal for the presence of an unretarded pairing contribution triggered by the spin-exchange interaction J can be discussed in this context.

A new imaging concept in spin polarimetry based on the spin-filter effect.

The concept of an imaging-type 3D spin detector, based on the combination of spin-exchange interactions in the ferromagnetic (FM) film and spin selectivity of the electron-photon conversion effect in a semiconductor heterostructure, is proposed and demonstrated on a model system. This novel multichannel concept is based on the idea of direct transfer of a 2D spin-polarized electron distribution to image cathodoluminescence (CL). The detector is a hybrid structure consisting of a thin magnetic layer deposited on a semiconductor structure allowing measurement of the spatial and polarization-dependent CL intensity from injected spin-polarized free electrons. The idea is to use spin-dependent electron transmission through in-plane magnetized FM film for in-plane spin detection by measuring the CL intensity from recombined electrons transmitted in the semiconductor. For the incoming electrons with out-of-plane spin polarization, the intensity of circularly polarized CL light can be detected from recombined polarized electrons with holes in the semiconductor. In order to demonstrate the ability of the solid-state spin detector in the image-type mode operation, a spin detector prototype was developed, which consists of a compact proximity focused vacuum tube with a spin-polarized electron source [p-GaAs(Cs,O)], a negative electron affinity (NEA) photocathode and the target [semiconductor heterostructure with quantum wells also with NEA]. The injection of polarized low-energy electrons into the target by varying the kinetic energy in the range 0.5-3.0 eV and up to 1.3 keV was studied in image-type mode. The figure of merit as a function of electron kinetic energy and the target temperature is determined. The spin asymmetry of the CL intensity in a ferromagnetic/semiconductor (FM-SC) junction provides a compact optical method for measuring spin polarization of free-electron beams in image-type mode. The FM-SC detector has the potential for realizing multichannel 3D vectorial reconstruction of spin polarization in momentum microscope and angle-resolved photoelectron spectroscopy systems.