Spin Coupling Research Articles

A high-efficiency, reliable multilevel hardware-accelerated annealer with in-memory spin coupling and complementary read algorithm

We proposed an in-memory spin coupler based on the 55 nm NOR flash technology to tackle the combinatorial optimization problems. The high-density and cost-effective floating-gate (FG) devices can overcome the capacity limitation in the conventional annealing machines based on static random access memory. In addition, the FG devices featuring high endurance and excellent data retention provide more robust annealing computation as compared to resistive random access memory. A novel complementary read algorithm is further developed to increase the tolerance on threshold voltage (V th) variation by 60%. Demonstrations show that the proposed in-memory spin coupling architecture with high efficiency and scalability has great potential for solving the combinatorial optimizations regardless of the problem size.

Fermions on curved backgrounds of matrix models

We discuss the propagation of fermions on generic, curved branes in Ishibashi-Kawai-Kitazawa-Tsuchiya-type matrix models. The Dirac operator can be understood either in terms of a Weitzenb\"ock connection, or in terms of the Levi-Civita connection with an extra torsion term. We discuss in detail the coupling of spin to the background geometry using the Jeffreys-Wentzel-Kramers-Brillouin approximation. Despite the absence of local Lorentz invariance in the underlying Ishibashi-Kawai-Kitazawa-Tsuchiya framework, our results agree with the expectations of Einstein-Cartan theory, and differ from general relativity only by an extra coupling to the totally antisymmetric part of the torsion. The case of Friedmann–-Lema\^{\i}tre-–Robertson-–Walker cosmic background solutions is discussed as a special case.

Spin to Charge Conversion in Semiconducting Antiferromagnetic Co3O4

Power efficient and faster spintronic devices require high spin current propagation efficiency from a ferromagnet (FM) to high spin orbit coupling material. Antiferromagnets (AFM) exhibiting high spin orbit coupling and faster spin dynamics have drawn great attention in such studies. Efficient spin current propagation in metallic AFMs via conduction electron showed promising results in spin to charge conversion physics. Recently, the insulating AFMs are also found to exhibit efficient spin current propagation due to the presence of magnonic modes. The semiconducting AFM Co3O4 is expected to show promising results in spin to charge conversion studies due to the simultaneous presence of magnon modes and conduction electrons. In this context, spin pumping and inverse spin Hall effect studies are carried out on a series of Co3O4(t nm)/Co(22 nm) samples where the t value varies from 0 to 26 nm. Damping analysis reveals that the spin diffusion length of Co3O4 is 2.5 ± 0.5 nm which is large in comparison to metallic AFMs. The maximum Hall angle of Co3O4 is found to be 0.26. A high spin transparency of 65.8% indicates efficient spin current propagation in the samples.

Impact of a non-magnetic Sr2+ ion doping on the magnetic and optical properties of Gd2-xSrxNiMnO6 (x = 0,0.3,0.5) double perovskite

The current study investigates the magnetization and optical characteristics of Sr-doped Gd2NiMnO6. Each sample's ZFC and FC magnetization measurements are presented. We discovered that the Curie temperature (TC) increases with doping. The ferromagnetic(FM) and antiferromagnetic(AFM) interactions cause different transitions in the pristine sample. The replacement of a non-magnetic Sr+2 ion reduces the Gd-Mn/Ni and Gd-Gd spin couplings, inhibiting AFM ordering and increasing the curie temperature for the doped sample in the low-temperature zone. Also decreased bandgap with doping was observed. Raman demonstrates two strong antisymmetric and symmetric modes, whereas FTIR shows two strong absorption bands caused by metal–oxygen stretching bands. Relying on the modified magnetic properties and also the calculated Eg values, the as-prepared samples might be used as a photocatalyst, and the reduction in bandgap owing to doping may find applications in solar cells.

Electron doping of a double-perovskite flat-band system

Electronic structure calculations indicate that the Sr2FeSbO6 double perovskite has a flat-band set just above the Fermi level that includes contributions from ordinary subbands with weak kinetic electron hopping plus a flat subband that can be attributed to the lattice geometry and orbital interference. To place the Fermi energy in that flat band, electron-doped samples with formulas Sr2-xLaxFeSbO6 (0 ≤ x ≤ 0.3) were synthesized, and their magnetism and ambient temperature crystal structures were determined by high-resolution synchrotron X-ray powder diffraction. All materials appear to display an antiferromagnetic-like maximum in the magnetic susceptibility, but the dominant spin coupling evolves from antiferromagnetic to ferromagnetic on electron doping. Which of the three subbands or combinations is responsible for the behavior has not been determined.

Spintronics and Optical Properties of Advanced Bio Materials

Spintronics is an interactive combination of electronics and magnetics that has grown in popularity in the twenty-first century as nanotechnology has advanced. Spintronics is a new type of electronics that employs mutual control of magnetic and other physical signals, such as electrical and optical signals. Spin current has recently received a lot of attention as a basic idea in spintronics. Understanding spin current entails deciphering the mechanisms underlying the mutual control of diverse physical signals, which should lead to future advances in spintronics. The notion of spin current and its historical context are discussed first in this chapter, followed by a discussion of innovative materials for spintronics. Much attention is also dedicated to the physical phenomena that result from the coupling of spins.

Signatures of the Bromine Atom and Open-Shell Spin Coupling in the X-ray Spectrum of the Bromobenzene Cation

Tabletop X-ray spectroscopy measurements at the carbon K-edge complemented by ab initio calculations are used to investigate the influence of the bromine atom on the carbon core-valence transitions in the bromobenzene cation (BrBz+). The electronic ground state of the cation is prepared by resonance-enhanced two-photon ionization of neutral bromobenzene (BrBz) and probed by X-rays produced by high-harmonic generation (HHG). Replacing one of the hydrogen atoms in benzene with a bromine atom shifts the transition from the 1sC* orbital of the carbon atom (C*) bonded to bromine by ∼1 eV to higher energy in the X-ray spectrum compared to the other carbon atoms (C). Moreover, in BrBz+, the X-ray spectrum is dominated by two relatively intense transitions, 1sC→π* and 1sC*→σ*(C*-Br), where the second transition is enhanced relative to the neutral BrBz. In addition, a doublet peak shape for these two transitions is observed in the experiment. The 1sC→π* doublet peak shape arises due to the spin coupling of the unpaired electron in the partially vacant π orbital (from ionization) with the two other unpaired electrons resulting from the transition from the 1sC core orbital to the fully vacant π* orbitals. The 1sC*→σ* doublet peak shape results from several transitions involving σ* and vibrational C*-Br mode activations following the UV ionization, which demonstrates the impact of the C*-Br bond length on the core-valence transition as well as on the relaxation geometry of BrBz+.

Interacting triplons in frustrated spin ladders: Binding and decay in BiCu2PO6

Establishing a comprehensive model of the rich spin dynamics in BiCu$_2$PO$_6$ has been a challenge over the last decade. Inelastic neutron scattering experiments revealed that its elementary triplons are non-degenerate showing the existence of significant anisotropic spin couplings. Evidence for triplon decay into two triplons has been found, but two prominent downturns in the dispersions eluded an explanation. Level repulsion due to hybridization of single triplons with the continuum of two-triplon scattering states has been proposed as explanation. We show that this concept may explain the weak downturn at higher energies, but fails for the most pronounced downturn at lower energy. In turn, we provide evidence that this downturn is the signature of a two-triplon bound state of essentially singlet character pointing to triplon-triplon interaction as the second crucial ingredient of the spin dynamics in this exemplary system.

Persistent spin helix on a diamond surface

Using first-principles calculations, we determine the impact of hydroxyl (OH) termination on the spin–orbit coupling (SOC) coefficient and spin texture of diamond surfaces. The persistent spin helix (PSH) state is revealed in the OH-terminated diamond (111) surface. The value of coefficient PSH α PSH was 14.2 meV·Å, which is larger than that of the zinc-blende n-type quantum well of GaAs/AlGaAs. The large α PSH is caused by the asymmetric charge density distribution near the surface rather than the size of the atomic SOC. The large α PSH will ensure the wavelength of PSH (λ PSH ), which will aid in the miniaturization of spintronic devices.

Structures and solvent effects on the 1H and 13C NMR chemical shifts of the family of three pro-lithospermate molecules: DFT study

The solvent effects on the structures and nuclear magnetic resonance spectroscopy of a series of three pro-lithospermate molecules are studied. These molecules include methyl pro-lithospermate, ethyl pro-lithospermate, and n-butyl pro-lithospermate, which exhibit enantiomers and diastereoisomers. The trans-oriented enantiomers were observed by Yu et al. [Nat. Prod. Res. 31(21), 2505–2512 (2017)] and are the subject of the present study. The density functional theory was validated using the gauge-including atomic orbital/B3LYP-D3BJ/6–31++G(d,p) and continuous set of gauge transformation (CSGT)/the long-range corrected Tao, Perdew, Staroverov, and Scuseria’s τ-dependent gradient-corrected correlation-exchange functional (LC-TPSS)TPSS/cc-pVTZ methods. The chemical shifts of 1H and 13C were calculated in dimethylsulfoxide (DMSO), methanol, and water. It turns out that solvent effects are weak on the geometrical parameters (bond lengths and bond angles). The harmonic oscillator model of the aromaticity index was used to calculate the aromaticity of the subunit rings. With regard to the available experimental results, the chemical shifts of 1H and 13C are reproduced better by B3LYP-D3BJ/6–31++G(d,p) than by LC-TPSSTPSS/cc-pVTZ in the DMSO medium. The solvent effects are significant on the 13C chemical shift, mostly for protic solvents, and insignificant on 1H. The vicinal spin–spin coupling constants of protons were calculated. The coupling constant of trans-olefinic and ortho-aromatic protons fits well with the experiment.

Simulating the Hamiltonian of dimer atomic spin model of one-dimensional optical lattice on quantum computers

The one-dimensional Ising model with its connections to several physical concepts plays a vital role in comprehension of several principles, phenomena and numerical methods. The Hamiltonian of a coupled one-dimensional dissipative spin system in the presence of magnetic field can be obtained from the Ising model. We simulate the above Hamiltonian by designing a quantum circuit with precise gate measurement and execute with the IBMQ experience platform through different [Formula: see text] states with controlled energy separation where we can check quantum synchronization in a dissipative lattice system. Our result shows the relation between various entangled states, the relation between the different energy separation ([Formula: see text]) with the spin–spin coupling ([Formula: see text]) in the lattice, along with fidelity calculations for several iterations of the model used. We also estimate the ground and first excited energy states of Ising-Hamiltonian using VQE algorithm and investigate the lowest energy values varying the number of layers of ansatz.

Spin dynamics in quantum dots on liquid helium

Liquid He-4 is free from magnetic defects, making it an ideal substrate for electrons with long-lived spin states. When electrons are localized in quantum dots and a strong magnetic field is applied along the surface, such states may serve as qubit states. A nonuniform magnetic field from a current-carrying wire submerged into helium enables switchable spin-orbit coupling. Bringing the frequency of orbital intradot vibrations close to the Larmor frequency allows for obtaining a strong Rashba electric dipole spin resonance and efficient interdot spin coupling. The authors show that the associated spin relaxation can be made sufficiently slow, permitting high-fidelity gate operations.

Electron-Coupled Proton Transfer Governed Magnetic Spin Couplings and Switching in Defect Nano Silicon Carbide

The formation mechanism, defect characterization, and potential applications of the Si vacancy (VSi) with internal H atoms in the silicon carbide (SiC) materials have been widely investigated. However, the inherent electronic properties and related phenomena induced by internal H dynamics in VSi, especially the C-radical spin interaction dynamics, are still poorly understood in such nano SiC. In this work, using the density functional calculations, we explore the magnetic coupling characteristics and dynamic behaviors induced by H-motion in nano SiC with four different types of H-doped VSi defect centers, (VSi + H)−, (VSi + H)+, (VSi + 2H), and NVH [i.e., (NCVSi + H)0 in which one of C-radical sites in VSi is replaced by N]. Our results reveal their unique ferromagnetic (FM) or antiferromagnetic (AFM) spin coupling characteristics and H-motion-induced interconversion. In general, the internal H-motion goes through the electron-coupled proton transfer (ECPT) in a C–H···C unit which has great impact on molecular orbitals, spin densities, and thus spin couplings among the C-radicals, allowing the VSi center to undergo magnetic switching between FM and AFM coupling. Interestingly, as in the (VSi + H)− center, such ECPT can further drive the excess electron delocalized on three C-radicals to gather at the ECPT unit, forming a three-center-four-electron (3c–4e) [C···H···C]− covalent H-bond with the switching of magnetic coupling. This work provides the dynamics insights into the spin coupling characteristics and its regulation by internal H-motion and multiple radical characters of such defect materials and the formation of a 3c–4e H-bond assisted by excess electron, and also provides inspired information for the design of inorganic magnetic materials and logic devices which can be controlled by interior doping and dopant dynamics.

Unveiling Electronic Behaviors in Heterochiral Charge-Density-Wave Twisted Stacking Materials with 1.25 nm Unit Dependence.

Layered charge-density-wave (CDW) materials have gained increasing interest due to their CDW stacking-dependent electronic properties for practical applications. Among the large family of CDW materials, those with star of David (SOD) patterns are very important due to the potentials for quantum spin liquid and related device applications. However, the spatial extension and the spin coupling information down to the nanoscale remain elusive. Here, we report the study of heterochiral CDW stackings in bilayer (BL) NbSe2 with high spatial resolution. We reveal that there exist well-defined heterochiral stackings, which have inhomogeneous electronic states among neighboring CDW units (star of David, SOD), significantly different from the homogeneous electronic states in the homochiral stackings. Intriguingly, the different electronic behaviors are spatially localized within each SOD with a unit size of 1.25 nm, and the gap sizes are determined by the different types of SOD stackings. Density functional theory (DFT) calculations match the experimental measurements well and reveal the SOD-stacking-dependent correlated electronic states and antiferromagnetic/ferromagnetic couplings. Our findings give a deep understanding of the spatial distribution of interlayer stacking and the delicate modulation of the spintronic states, which is very helpful for CDW-based nanoelectronic devices.

Interlayer Chemical Modulation of Phase Transitions in Two-Dimensional Metal Chalcogenides.

Two-dimensional metal chalcogenides (2D-MCs) with complex interactions are usually rich in phase transition behavior, such as superconductivity, charge density wave (CDW), and magnetic transitions, which hold great promise for the exploration of exciting physical properties and functional applications. Interlayer chemical modulation, as a renewed surface modification method, presents congenital advantages to regulate the phase transitions of 2D-MCs due to its confined space, strong guest-host interactions, and local and reversible modulation without destructing the host lattice, whereby new phenomena and functionalities can be produced. Herein, recent achievements in the interlayer chemical modulation of 2D-MCs are reviewed from the aspects of superconducting transition, CDW transition, semiconductor-to-metal transition, magnetic phase transition, and lattice transition. We systematically discuss the roles of charge transfer, spin coupling, and lattice strain on the modulation of phase transitions in the guest-host architectures of 2D-MCs established by electrochemical intercalation, solution-processed intercalation, and solid-state intercalation. New physical phenomena, new insight into the mechanism of phase transitions, and derived functional applications are presented. Finally, a prospectus of the challenges and opportunities of interlayer chemical modulation for future research is pointed out.

Spirobifluorene Mediating the Spin–Spin Coupling of Nitronyl Nitroxide Diradicals

To investigate the mechanism of this spiro conjugation magnetic behavior, we designed and synthesized three diradicals─22'SBF-NN, 44'SBF-NN, and 27SBF-NN. They are bridged by spirobifluorene and nitronyl nitroxide (NN) diradicals as the spin centers. Notably, by SQUID and electron paramagnetic resonance (EPR) zero-field splitting data analyses, the 22'SBF-NN and 27SBF-NN diradicals exhibit intramolecular, distinctly antiferromagnetic (AF) coupling, with 2J(22'SBF-NN)/kB = -5.86 K and 2J(27SBF-NN)/kB = -24.6 K, respectively. The AF of 22'SBF-NN is opposite to that predicted by the spin density alternation rule based on Hund's rule. Diradical intramolecular conjugation coupling bridged by spiro-carbon conjugation is discussed, in which the 22'SBF-NN is smaller than that of 27SBF-NN, corresponding to the room-temperature EPR characterization. This spiro conjugation is weaker than the traditional planar conjugation and generally leads to a weaker spin-spin coupling in the helical biradical molecule. The EPR spectrum of the 44'SBF-NN diradical shows a deformed nine-line curve, indicating intramolecular exchange coupling. The density functional theory calculation gives a very weak coupling constant of 2Jcalc/kB = 0.06 K, with ferromagnetic (FM) interaction as the proof, which is consistent with the spin-polarized prediction. Further analysis of magnetic susceptibility χm and VT-EPR data shows that there is indeed an extremely weak FM interaction in the 44' position diradical. We find the bridge, which is a 44' substituted SBF structure, blocks the conjugation and contains a larger twist in steric hindrance, which also hampers sufficient spin density delocalization, resulting in a much weaker spin coupling interaction. Combined with the analysis of molecular orbital calculation results, the anomalous intramolecular AF coupling mechanism of 22'SBF-NN is further explained.

Magnetic moment impact on spin-dependent Seebeck coefficient of ferromagnetic thin films

Magnetic materials may be engineered to produce thermoelectric materials using spin-related effects. However, clear understanding of localized magnetic moments (µI), free carriers, and Seebeck coefficient (S) interrelations is mandatory for efficient material design. In this work, we investigate µI influence on the spin-dependent S of model ferromagnetic thin films, allowing µI thermal fluctuations, ordering, and density variation influence to be independently investigated. µI influence on free carrier polarization is found to be of highest importance on S: efficient coupling of free carrier spin and localized magnetic moment promotes the increase of S, while spin-dependent relaxation time difference between the two spin-dependent conduction channels leads to S decrease. Our observations support new routes for thermoelectric material design based on spin-related effects in ferromagnetic materials.

Spin-photogalvanic effect in chiral lead halide perovskites.

Low-temperature solution-made chiral lead halide perovskites (LHPs) have spontaneous Bychkov-Rashba spin orbit coupling (SOC) and chiral-induced spin selectivity (CISS) qualities. Their coexistence may give rise to considerable spin and charge conversion capabilities for spin-orbitronic applications. In this study, we demonstrate the spin-photogalvanic effect for (R-MBA)2PbI4 and (S-MBA)2PbI4 polycrystalline film-based lateral devices (100 μm channel length). The light helicity dependence of the short-circuit photocurrent exhibits the circular photogalvanic effect (CPGE) and linear photogalvanic effect (LPGE) with decent two-fold symmetry for a complete cycle in a wide temperature range from 4 K to 300 K. Because of the Rashba SOC and the material helicity, the effect is converse for the two chiral LHPs. In addition, its magnitude and sign can be effectively tuned by constant magnetic fields. The Rashba effect, CISS-generated unbalanced spin transport, and chiral-induced magnetization are mutually responsible for it. Our study evidently proves the future prospect of using chiral LHPs for spin-orbitronics.

Hydrogen-migration governed dynamic magnetic coupling characteristics in nitrogen-vacancy-hydrogen nanodiamonds.

The nitrogen-vacancy center doped with hydrogen (NVH) is one of the most common defects in diamonds, and the doping of hydrogen is known to enable mobility among three equivalent C-radicals in the defect, which noticeably affects the spin coupling among the radicals. Here, we for the first time uncover the dynamic nature of magnetic coupling induced by H-migration in the NVH center of nanodiamonds, using spin-polarized density functional theory calculations and enhanced sampling metadynamics simulations. The mobility of doping H enables the interior NVH region to become a variable magnetic space (antiferromagnetic/AFM versus ferromagnetic/FM). That is, the dynamic H has three frequently reachable binding C sites where H enables the center to exhibit variable AFM coupling (high up to J = -1282 cm-1) and that in other H-reachable regions including N sites, it enables the center to exhibit FM coupling (high up to J = 598 cm-1). The magnetic switching (AFM ↔ FM) and strength fluctuation strongly depend on the H-position which can adjust the ratio of the C radical orbitals in their mixing orbitals for a special three-electron three-center covalent C⋯H⋯C H-bonding and radical orbital distributions. Clearly, this work provides insights into the dynamic switching of magnetic coupling in such multi-radical centers of defect nanodiamonds.

Proton-transfer regulated magnetic coupling characteristics in Blatter-based diradicals

We computationally design Blatter-based diradicals by adding a radical group as an additional spin source and explore their magnetic spin coupling characteristics and proton-transfer regulation.