Small Spin Research Articles

Light-cone sum rules study on the purely nonfactorizable Λc+→Ξ0K+ decay

We investigate the purely nonfactorizable Λc+→Ξ0K+ decay using light-cone sum rules. To extract the decay amplitudes, a three-point correlation function is defined and calculated at hadron and quark-gluon level, respectively. Both the W-exchange and the W-inward emission diagrams are considered in the quark-gluon level calculation, where the two-particle light-cone distribution amplitudes (LCDAs) of kaon are used as nonperturbative input. We obtain the decay amplitudes contributed from the twist-2 and twist-3 kaon LCDAs, respectively. The obtained P-wave amplitude is consistent with those predicted in the literature, while the S-wave one is much smaller. This significant difference between the S- and P -wave amplitudes leads to small up-down spin asymmetry, close to the experimental measurement. Published by the American Physical Society 2024

On the non-dissipative orbital evolution of a binary system comprising non-compact components with misaligned spin and orbital angular momenta

Abstract In this Paper we determine the non-dissipative tidal evolution of a close binary system with an arbitrary eccentricity in which the spin angular momenta of both components is misaligned with the orbital angular momentum. We focus on the situation where the orbital angular momentum dominates the spin angular momenta and so remains at small inclination to the conserved total angular momentum. Torques arising from rotational distortion and tidal distortion taking account of Coriolis forces are included. This extends the previous work of Ivanov & Papaloizou relaxing the limitation resulting from the assumption that one of the components is compact and has zero spin angular momentum. Unlike the above study, the evolution of spin-orbit inclination angles is driven by both types of torque. We develop a simple analytic theory describing the evolution of orbital angles and compare it with direct numerical simulations. We find that the tidal torque prevails near ’critical curves’ in parameter space where the time-averaged apsidal precession rate is close to zero. In the limit of small spin, these curves exist only for systems that have at least one component with retrograde rotation. As in our previous work, we find solutions close to these curves for which the apsidal angle librates. As noted there, this could result in oscillation between prograde and retrograde states. We consider the application of our approach to systems with parameters similar to those of the misaligned binary DI Herc.

Spin-Hall conductivity and optical characteristics of noncentrosymmetric quantum spin Hall insulators: the case of PbBiI

Quantum spin Hall insulators have attracted significant attention in recent years. Understanding the optical properties and spin Hall effect in these materials is crucial for technological advancements. In this study, we present theoretical analyses to explore the optical properties, Berry curvature and spin Hall conductivity of pristine and perturbed PbBiI using the linear combination of atomic orbitals and the Kubo formula. The system is not centrosymmetric and it is hosting at the same time Rashba spin-splitting and quantized spin Hall conductivity. Our calculations reveal that the electronic structure can be modified using staggered exchange fields and electric fields, leading to changes in the optical properties. Additionally, the spin Berry curvature and spin Hall conductivity are investigated as a function of the energy and temperature. The results indicate that due to the small dynamical spin Hall conductivity, generating an ac spin current in the PbBiI requires the use of external magnetic fields or magnetic materials.

Control of spin-wave polarity and velocity using a ferrimagnetic domain wall

We present a theoretical study of the scattering of spin waves by a domain wall (DW) in a ferrimagnetic (FiM) spin chain in which two sublattices carry spins of unequal magnitudes. We find that a narrow but atomically smooth FiM DW exhibits a different behavior in comparison with similarly smooth ferromagnetic and antiferromagnetic DWs due to the inequivalence of the two sublattices. Specifically, for sufficiently weak anisotropy, the smaller spin at the center of the DW is found to become precisely normal to the easy axis, selecting an arbitrary direction in the xy plane and thereby breaking the U(1) spin-rotational symmetry spontaneously. This particular form of a FiM DW does not occur in antiferromagnetic systems and is shown to lead to a strong dependence of spin-wave scattering pattern on the state of polarization of the spin wave, which can be either right-handed or left-handed, suggesting the utilization of such a narrow DW as a spin-wave filter. Moreover, we find that in the case of an atomically sharp DW, where all the spins point either up or down due to strong easy-axis anisotropy and therefore the polarization of the spin wave is conserved upon transmission, the wave vector of the spin-wave changes after passing through the DW leading to a change in the group velocity of the spin wave. This change of the wave vector indicates the acceleration or deceleration of the spin waves and thus a sharp FiM DW could serve as a spin-wave accelerator or decelerator in spintronics devices, offering a functionality absent in a ferromagnetic and an antiferromagnetic counterpart. Our results indicate that FiM spin textures can interact with spin waves distinctly from ferromagnetic and antiferromagnetic counterparts, suggesting that they may offer spin-wave functionalities that are absent in more conventional magnets. Published by the American Physical Society 2024

A [Mn8] Defective Supertetrahedron T3 and Its Dimeric [Mn16] Analogue.

The initial use of 2-(pyridin-2-yl)propane-1,3-diol (pypdH2) in Mn cluster chemistry has afforded two new mixed-valence polynuclear Mn clusters, namely, [Mn8Ο5(pypd)(hmp)3(O2CCMe3)8] (1) and [Mn16Ο10(N3)2(pypd)2{(py)2CO2}4(O2CEt)12] (2) (hmp- = deprotonated 2-hydroxymethylpyridine; (py)2CO2 2- = deprotonated gem-diol form of di-2-pyridyl ketone). Compound 1 features a novel [MnIII 7MnII(μ4-O)2(μ3-O)3(μ-OR)5]8+ structural core resembling a supertetrahedron T3, lacking two apexes, while complex 2 has a [MnIII 14MnII 2(μ4-O)4(μ3-O)6(μ-N3)2(μ3-OR)2(μ-OR)8]14+ core consisting of two [Mn8] subunits related to 1 and thus is a dimeric analogue of 1. Direct current (dc) magnetic susceptibility studies revealed the presence of dominant antiferromagentic exchange interactions between the Mn ions in complexes 1 and 2 and small ground state spin values for both compounds. Overall, this work highlights the capability of polyol-like chelates like pypdH2 to stabilize high nuclearity 3d metal clusters based on polynuclear building blocks.

Magnetic resonance imaging of the cerebellopontine angle: comparison between constructive interference steady-state and small field-of-view technique turbo spin echo sequences.

The aim of this work was to optimize athree-dimensional (3D) turbo-spin-echo (TSE) sequence using asmall field-of-view (FOV) technique for the study of the cerebellopontine angle and to compare it with aconstructive interference steady-state (CISS) sequence. A total of 30consecutive patients underwent magnetic resonance imaging with a3Tesla (T) scanner, including 3D CISS and the optimized 3D small FOV technique turbo spin echo (3D SFT-TSE) T2-weightedsequences for the study of the cerebellopontine angle. The 3D SFT-TSE sequence was optimized after three different steps, and aquantitative evaluation of the signal-to-noise ratio (SNR) was obtained according to the National Electrical Manufacturers Association (NEMA) method. Three neuroradiologists made ablind comparative qualitative evaluation of the images between the 3D CISS and the 3D SFT-TSE obtained after the third optimization step, based on spatial resolution, contrast resolution, and presence of artifacts and noise. The calculation of SNR using the NEMA method confirmed the superiority of the third optimization step over the others. For both spatial and contrast resolution, the optimized SFT-TSE was considered better (p < 0.001) than the CISS, while image artifacts and noise were considered worse in the CISS sequence (p < 0.001). Intraobserver analysis showed that all neuroradiologists preferred the 3D SFT-TSE sequence in terms of both spatial resolution and contrast resolution and found more noise and artifact disruption in the CISS sequence. The use of the 2D radiofrequency pulse technique with a3D SFT-TSE T2 sequence was significantly more efficient than the 3D CISS sequence for the study of the cerebellopontine angle and inner ear structures.

Numerical simulation of RHIC polarized proton run 17 spin flipper experiments

RHIC nine-magnet spin flipper has been operated successfully during RHIC polarized proton Run 17, with 97% spin flip efficiency achieved. The results show the importance of mirror resonance removal, small spin tune spread, and proper spin flipper driving tune sweep speed. Detailed spin tracking simulations, based on a Lorentz force and Thomas-BMT differential equation numerical solver code for accuracy, have been carried out to understand the experimental results. Agreement within measurement accuracy is obtained at injection energy, 23.8 GeV. It is not as tight at 255 GeV, reasons for that are exposed. These measurements and numerical studies allow to determine the sensitivity of spin-flip efficiency to the dispersion slopes at the two Siberian snakes and to the ac dipole frequency sweep speed. They also provide guidance for future developments at BNL’s electron-ion collider. Published by the American Physical Society 2024

Complete realization of energy landscapes and non-equilibrium trapping dynamics in small spin glass and optimization problems

Energy landscapes are high-dimensional surfaces underlie all physical systems, which determine crucially the energetic and behavioral dependence of the systems on variable configurations, but are difficult to be analyzed due to their high-dimensional nature. Here we introduce an approach to reveal for the complete energy landscapes of spin glasses and Boolean satisfiability problems with a small system size, and unravels their non-equilibrium dynamics at an arbitrary temperature for an arbitrarily long time. Remarkably, our results show that it can be less likely for the system to attain ground states when temperature decreases, due to trapping in individual local minima, which ceases at a different time, leading to multiple abrupt jumps in the ground-state probability. For large systems, we introduce a variant approach to extract partially the energy landscapes and observe both semi-analytically and in simulations similar phenomena. This work introduces new methodology to unravel the energy landscapes and non-equilibrium dynamics of glassy systems, and provides us with a clear, complete and new physical picture on their long-time behaviors inaccessible by existing approaches.

Terahertz magnetic excitation in a collinear antiferromagnet: Canonical transformation model and atomistic spin simulations

In this study, simple canonical transformation theory is introduced to describe the current-driven magnetization dynamics in collinear antiferromagnets. The theory is confirmed by atomistic level dynamical simulations performed in an antiferromagnetic L10-type MnPt sample. The simulations indicate that when a small spin polarized current is perpendicularly applied to the MnPt sample, a stable initial stationary state remains with a perpendicular antiferromagnetic structure. For a current larger than a threshold, the transition from a stationary state to a stable in-plane precession state is observed without any assistance of magnetic fields, accompanied by a generation of terahertz magnetic signals. The simulations show a good agreement with the analytical theory, from which we could gain a comprehensive understanding of current-induced magnetization dynamics in collinear antiferromagnets at the atomic level.

Coupled spin-lattice dynamics from the tight-binding electronic structure

We developed a method which performs the coupled adiabatic spin and lattice dynamics based on the tight-binding electronic structure model, where the intrinsic magnetic field and ionic forces are calculated from the converged self-consistent electronic structure at every time step. By doing so, this method allows us to explore limits where the physics described by a parameterized spin-lattice Hamiltonian is no longer accurate. We demonstrate how the lattice dynamics is strongly influenced by the underlying magnetic configuration, where disorder is able to induce significant lattice distortions. The presented method requires significantly less computational resources than methods, such as time-dependent density functional theory (TD-DFT). Compared to parameterized Hamiltonian-based methods, it also describes more accurately the dynamics of the coupled spin and lattice degrees of freedom, which becomes important outside of the regime of small lattice and spin fluctuations. Published by the American Physical Society 2024

Quantum phase transitions in the alternating XY chain with three-site interactions

We investigate the quantum phase transition in the alternating XY chain with the XZY+YZX type of three-spin interactions. We present the exact solution derived by means of the Jordan–Wigner transformation and study the average magnetization, spin correlations, and von Neumann entropy to establish the phase diagram. The phase diagram consists of the ferromagnetic phases, the paramagnetic phases, and the phase with weak magnetization (WM). By examining the nearest-neighbor transverse spin correlation, we probe that in the WM phase, the spins within a supercell generate a cluster with a small total spin, but between the nearest-neighbor supercells are distributed randomly. Especially for the dimerized limit case, the spins within a supercell tend to point to opposite directions of the transverse field. In addition, we also investigate the influence of the three-site interaction, and find that the WM phase is absent as the strength of the three-site interaction increases. Our findings shed light on the complex behavior of the alternating XY chain and provide valuable insights for future studies.

Skyrmion based universal logic gates and computation operation

Swirling spin configurations with a non-trivial topological state are popularly known as magnetic skyrmions. They are often observed in magnetic thin films with perpendicular magnetic anisotropy and Dzyaloshinskii–Moriya interaction (DMI). Due to their small size and non-collinear spin texture, they are being considered as a potential candidate for spintronic devices such as data storage devices, and logic-based devices. These skyrmions have distinct properties and interactions, that can be utilized to control their movement by applying an external electric current. In this work, we have successfully demonstrated the operation of skyrmion-based universal NAND and NOR logic gates. We have further performed arithmetic addition of two and three single-bit by using a half and full adder, fabricated based on the XOR and AND gates. We have observed that the presence of only uniform DMI is not enough to achieve all logic operations. The presence of a negative DMI at the edges is crucial in achieving proper logic operations. The findings are very important for the realization of skyrmion-based logic and computational operations.

Discovery and Characterization of Antiferromagnetic UFe5As3.

This work presents a study on a new uranium iron arsenide UFe5As3. By implementing Bi-flux synthesis, we were able to grow mm-sized single crystals of this compound, which show twinning. UFe5As3 is one of only two known uranium iron arsenides. It adopts a monoclinic, UCr5P3-type crystal structure (space group P21/m, Pearson symbol mP18, a = 7.050(2) Å, b = 3.8582(9) Å, c = 9.634(1) Å, β = 100.25(1)°). The magnetic susceptibility of UFe5As3 indicates it to be an antiferromagnet with TN = 47 K and μeff = 4.94 μB per formula unit, signaling that both U and Fe are likely magnetic in this material. The material appears to be anisotropic, with a small (likely ferromagnetic) spin reorientation transition around T = 29 K. The Sommerfeld coefficient γ0 = 135 mJ mol-1 K-2 suggests enhanced effective electron mass in UFe5As3, while electrical resistivity indicates metallic, Kondo-like behavior.

Quantum phase transitions in skewed ladder systems.

In this brief review, we introduce a new spin ladder system called skewed spin ladders and discuss the exotic quantum phases of this system. The spin ladders studied are the 5/7, 3/4 and 3/5 systems corresponding to alternately fused 5 and 7 membered rings; 3 and 4 membered rings; and 3 and 5 membered rings. These ladders show completely different behaviour as the Hamiltonian model parameter is changed. When the Hamiltonian parameter is increased the 5/7 ladder switches from an initial singlet ground state to progressively higher spin ground state and then to a reentrant singlet state before finally settling to the highest spin ground state whose spin equals the number of unit cells in the system. The 3/4 ladder goes from a singlet ground state to a high spin ground state with each unit cell contributing spin 1 to the state, as the model parameter is increased. The 3/5 ladder shows a singlet ground state for small parameters and high spin ground state for intermediate values of the parameter and for still higher parameters, a reentrant singlet ground state. They can also show interesting magnetization plateaus as illustrated by studies on a specific spin ladder.

Standing spin waves in finite quantum spin spiral chains

Standing spin waves in quantum spin-spiral chains are investigated using the local Pn and total absorbed power P. This method allows the investigation of the spin wave pattern and dispersion even if the quantum mechanical spin system initially has no magnetic order due to quantum fluctuations. In addition, the spin dynamics during resonance were examined more closely. Without taking damping into account, a multi-spin Rabi oscillation can be observed. The Rabi Oscillation disappears when damping is taken into account. The cause of this behavior becomes apparent when looking at the spin wave excitation in the semi-classical description. In the semi-classical description, also a Rabi oscillation occurs, which will be prevented by damping. The cause of the semi-classical Rabi oscillation is to be found in the effective field, which periodically drives the spins out of the equilibrium position or brings them in. The damping creates a spin torque directed against the effective field’s spin torque which results in small spin oscillations around its equilibrium position.

Orbital Hanle Magnetoresistance in a 3d Transition Metal.

The Hanle magnetoresistance is a telltale signature of spin precession in nonmagnetic conductors, in which strong spin-orbit coupling generates edge spin accumulation via the spin Hall effect. Here, we report the existence of a large Hanle magnetoresistance in single layers of Mn with weak spin-orbit coupling, which we attribute to the orbital Hall effect. The simultaneous observation of a sizable Hanle magnetoresistance and vanishing small spin Hall magnetoresistance in BiYIG/Mn bilayers corroborates the orbital origin of both effects. We estimate an orbital Hall angle of 0.016, an orbital relaxation time of 2ps and diffusion length of the order of 2nm in disordered Mn. Our findings indicate that current-induced orbital moments are responsible for magnetoresistance effects comparable to or even larger than those determined by spin moments, and provide a tool to investigate nonequilibrium orbital transport phenomena.

Blandford–Znajek process in Einsteinian cubic gravity

In this paper, we investigate the Blandford–Znajek (BZ) process within the framework of Einsteinian cubic gravity (ECG). To analytically study the BZ process using the split monopole configuration, we construct a slowly rotating black hole in ECG up to cubic order in small spin, considering the leading order in small coupling constant of higher curvature terms. By deriving the magnetosphere solution around the black hole, we determine the BZ power up to the second relative order in spin. The BZ power is modified by the coupling constant compared to Kerr black hole case. Although the general nature of the BZ process in ECG remains unchanged at the leading order in spin, the coupling constant introduces modification at the second relative order in spin. Therefore, we anticipate that it is feasible to discern general relativity from higher derivative gravities by examining the BZ power in rapidly rotating black holes.

Achieving short-wavelength free radical emission by combining small conjugated structure and anti-Kasha emission

Since the natural narrow bandgaps of free radicals usually lead to emission in the long-wavelength region, it is still of great challenge to design radical luminescent materials with stable and short-wavelength emission in the ambient environment. In this work, a series of dicarbonyl-substituted organic molecules with small conjugated structures were used to form free radicals with short-wavelength radical emission. These low-conjugated molecules with only one benzene ring showed stable photoinduced free radical emission after doping with polymethyl methacrylate (PMMA) because the rigid polymer environment could help stabilize the free radicals and limit the non-radiative energy transfer. Moreover, PMMA with electron-withdrawing groups could promote the generation of carbonyl radical cations. The theoretical calculation suggests that the free radical with anti-Kasha emission derived from high energy excited state (D4 or D5) would directly relax to the ground state, combining with the small spin delocalization of the low conjugation free radical, leading to short-wavelength emission. More importantly, such free radical emissions could also respond to external stimulation such as light irradiation or heat treatment. These materials show great potential in lithography information recording and information encryption. This design strategy provides new insights into molecular and functional diversity of free radical materials.

Kinetic Studies of WO3-Based Photochromism in Polyvinyl Alcohol Film.

Tungsten oxide (WO3) has been extensively studied for various photochromic applications. Blue coloration of WO3 is explained in terms of the intervalence charge transfer (IVCT) transition of electrons between W6+ and W5+. However, various absorption spectra with different shapes have been reported. Herein, a transparent film was prepared by drying aqueous solutions containing polyvinyl alcohol, WO3 nanoparticles and ethylene glycol (EG). For comparison, the photochromic behavior of an aqueous WO3 colloidal solution containing EG was also investigated. Under UV irradiation, a single intense peak was always observed at ca. 777 nm in the colloidal solution, but the absorption spectra of the film changed from a peak at 770 nm to two distinct peaks at 654 and 1003 nm. All absorption spectra observed with the film and the colloidal solution were deconvoluted into five peaks at 540, 640, 775, 984, and 1265 nm. Kinetic studies using the colloidal solution indicated that the coloration rates (r0) estimated at the deconvoluted peaks of 640, 775, and 984 nm followed the same rate law. On the other hand, in the case of the film, r0 evaluated at 640 or 984 nm was independent of the water amounts but increased proportionally to the EG amounts and the light intensity, although r0 at 775 nm significantly increased with the increasing amounts of water and EG. Raman and electron spin resonance spectroscopic observations of the film revealed that the photogenerated electrons migrated toward the terminal W═O moiety to accumulate and then a small anisotropic electron spin resonance signal appeared. Our study demonstrates that the absorption at 775 nm is due to IVCT between W6+ and W5+, which is stabilized with water in the bulk and the absorption peaks at 640 and 984 nm are attributable to IVCT on the WO3 surface.

Averaging of the free induction decay from an ensemble of small spin clusters

Averaging of the free induction decay from an ensemble of small spin clusters