Spin Rotation Research Articles

Study of the effect of ethanol on the properties of poloxamer 338 solutions by rotational viscometry and spin probe method

The aim. Study the properties of 20 % solutions of poloxamer 338 (P338) in water and mixed solvents water-ethanol using rotational viscometry and the spin probe method at various temperatures. Materials and methods. 20 % m/m solutions of P338 in water and water – ethanol mixtures were the objects of research. The solutions were studied by rotational viscometry at various temperatures; the flow behaviour, lower yield stress (t0) and dynamic or apparent viscosity (η) were determined. Spin probes based on fatty acids, which differ in molecular structure, solubility, and radical localization, were added to the solutions. Electron paramagnetic resonance (EPR) spectra were obtained to determine their type and parameters. Results. Depending on the content, ethanol affects the rheological properties of 20 % solution of P338. The solution was demonstrated to be able to thermally induce sol → gel transition at 32 °C when ethanol content is 5 % m/m. The rheological parameters of the gel at 32 °C and 37 °C exhibit an increase (in comparison to the gel without ethanol), accompanied by a reduction in the packing density of polypropylene oxide (PPO) chains within the cores of P338 micelles. At an ethanol content of 10 % m/m, the gel formation temperature rises to 40 °C. At ethanol content of 15 % m/m and above, 20 % P338 solutions do not form gels at temperatures between 25 °C and 40 °C. The values of rotational correlation times (τ) and the order parameter (S) of fatty acid-based spin probes were observed to decrease with increasing ethanol content up to 30 % m/m; in the case of the ammonium salt of 5‑doxylstearic acid (5-DSA NH4 salt), the anisotropic EPR spectra transform, becoming a superposition of two triplets and subsequently a triplet. P338 solutions retain their ability to undergo thermally induced sol ↔ gel transitions as long as the EPR spectra of this probe exhibit anisotropy at temperatures ranging from 25 °C to 37 °C. As the concentration of ethanol in the solution increases, the solvation of the cores of P338 micelles by the dispersion medium of the solution also increases. Conclusions. It was demonstrated that ethanol, when added to the 20 % P338 solution, results in changes to the rheological properties of this solution. However, at the ethanol content of 5-10 % m/m, the ability of P338 to thermally induce sol → gel transition remains unaltered. The rheological properties of the 20 % P338 solution exhibit a correlation with the observed change in EPR spectra types for the 5-DSA NH4 salt. As the ethanol content in the solution increases, the solvation of P338 micelle cores by the dispersion medium increases, accompanied by decreased density and orderliness of the PPO chains packing in the micelle cores

Observation of Mermin-Wagner behavior in LaFeO3/SrTiO3 superlattices

Two-dimensional magnetic materials can exhibit new magnetic properties due to the enhanced spin fluctuations that arise in reduced dimension. However, the suppression of the long-range magnetic order in two dimensions due to long-wavelength spin fluctuations, as suggested by the Mermin-Wagner theorem, has been questioned for finite-size laboratory samples. Here we study the magnetic properties of a dimensional crossover in superlattices composed of the antiferromagnetic LaFeO3 and SrTiO3 that, thanks to their large lateral size, allowed examination using a sensitive magnetic probe — muon spin rotation spectroscopy. We show that the iron electronic moments in superlattices with 3 and 2 monolayers of LaFeO3 exhibit a static antiferromagnetic order. In contrast, in the superlattices with single LaFeO3 monolayer, the moments do not order and fluctuate to the lowest measured temperature as expected from the Mermin-Wagner theorem. Our work shows how dimensionality can be used to tune the magnetic properties of ultrathin films.

Extracting off-diagonal order from diagonal basis measurements

Quantum gas microscopy has developed into a powerful tool to explore strongly correlated quantum systems. However, discerning phases with topological or off-diagonal long range order requires the ability to extract these correlations from site-resolved measurements. Here, we show that a multiscale complexity measure can pinpoint the transition to and from the bond ordered wave phase of the one-dimensional extended Hubbard model with an off-diagonal order parameter, sandwiched between diagonal charge and spin density wave phases, using only diagonal descriptors. We study the model directly in the thermodynamic limit using the recently developed variational uniform matrix product states algorithm, and draw our samples from degenerate ground states related by global spin rotations, emulating the projective measurements that are accessible in experiments. Our results will have important implications for the study of exotic phases using optical lattice experiments. Published by the American Physical Society 2024

Spin and valley-polarized Faraday rotation in irradiated buckled Xene materials

This study delves into the theoretical exploration of Faraday rotation and ellipticity in light beams transmitted through buckled Xene materials. These materials undergo topological phase transitions (TPTs), shifting from topologically non-trivial to trivial systems under the influence of an off-resonance irradiated laser field or a staggered electric potential. Specifically, we investigate the manifestation of these phenomena when the buckled Xene material is exposed to an off-resonant laser and staggered sublattice potential. Using the Kubo formula, we derive the optical conductivities of the buckled Xene material to analyze transmission spectra through Fresnel’s transmission coefficients. Additionally, we calculate the spin and valley-dependent Faraday rotation angles and ellipticities of the buckled Xene by selecting suitable parameters for the circularly polarized off-resonant laser field and staggered electric potential across distinct topological quantum phases. Our findings reveal a high sensitivity of Faraday rotation and ellipticity to the topological invariants. In particular, we find that due to the broken time-reversal symmetry (TRS), the amount of the maximum spin and valley polarized Faraday rotation angle and ellipticity in irradiated buckled Xene material without magnetic field are ≊±0.53∘ and ≊±0.2∘, respectively. Our results suggest possible techniques for probing topological numbers and topological phase transitions in buckled Xene materials by Faraday rotation.

Improving the beam quality of the low-energy muon beamline at Paul Scherrer Institute: Characterization of ultrathin carbon foils

The low-energy muon (LEM) beamline at the Paul Scherrer Institute currently stands as the world’s only facility providing a continuous beam of low-energy muons with keV energies for conducting muon spin rotation experiments on a nanometer depth scale in heterostructures and near a sample’s surface. As such, optimizing the beam quality to reach its full potential is of paramount importance. One of the ongoing efforts is dedicated to improving the already applied technique of single muon tagging through the detection of secondary electrons emerging from an ultrathin carbon foil. In this work, we present the results from installing a thinner foil with a nominal thickness of 0.5 μg cm−2 and compare its performance to that of the previously installed foil with a nominal thickness of 2.0 μg cm−2. Our findings indicate improved beam quality, characterized by smaller beam spots, reduced energy loss and straggling of the muons, and enhanced tagging efficiency. Additionally, we introduce a method utilizing blue laser irradiation for cleaning the carbon foil, further improving and maintaining its characteristics. Published by the American Physical Society 2024

Penetration of a spinning sphere impacting a granular medium.

We investigate experimentally the influence of rotation on the penetration depth of a spherical projectile impacting a granular medium. We show that a rotational motion significantly increases the penetration depth achieved. Moreover, we model our experimental results by modifying the frictional term of the equationdescribing the penetration dynamics of an object in a granular medium. In particular, we find that the frictional drag decreases linearly with the velocity ratio between rotational (spin motion) and translational (falling motion) velocities. The good agreement between our model and our experimental measurements offers perspectives for estimating the depth that spinning projectiles reach after impacting onto a granular ground, such as happens with seeds dropped from aircraft or with landing probes.

Cooling method for the rotor of a superconducting motor

Electrification has been proposed as a route to decarbonizing air travel. Conventional electric motors are too heavy to achieve the power densities required for aviation so superconducting motors for aircraft are being developed. Superconductors however, work at cryogenic temperatures, which indispensably require a reliable and efficient cooling mechanism with a cryocooler. The Robinson Research Institute is developing a 3 MW superconducting motor using an HTS (High Temperature Superconductor) rotor operating at 50 K and MgB2 running at near 20 K for the stator. The motor is intended to run at a shaft speed of 4500-6000 rpm to directly drive a ducted fan. A key challenge is the removal of heat from a cryogenic spinning rotor to a stationary refrigerator so it can be rejected at ambient temperatures. Previous motors have utilized externally pumped or thermos-syphoned cryogens to cool the rotor, which require complex rotary seals. The aircraft application demands a compact and low weight solution. This paper presents a novel cooling design where a stationary cryocooler’s cold heat exchanger penetrates the rotor, and the relative motion of the two creates a pumping motion for cold helium gas to transfer heat from the rotor to the cryocooler. The sealing is low pressure and at ambient temperature and pressure with a temperature gradient in the helium adjacent to the cryocooler regenerator. Design and CFD modelling of the concept are presented showing the system can generate sufficient cold helium flow to transfer heat from the rotor to the cryocooler with a small temperature difference, resulting in a compact, efficient, and low-weight rotor cooling method.

Spin Rotations in a Bose-Einstein Condensate Driven by Counterflow and Spin-Independent Interactions.

We observe spin rotations caused by atomic collisions in a nonequilibrium Bose-condensed gas of ^{87}Rb. Reflection from a pseudomagnetic barrier creates counterflow in which forward- and backward-propagating matter waves have partly transverse spin directions. Even though inter-atomic interaction strengths are state independent, the indistinguishability of parallel spins leads to spin dynamics. A local magnetodynamic model, which captures the salient features of the observed spin textures, highlights an essential connection between four-wave mixing and collisional spin rotation. The observed phenomenon is commonly thought not to occur in Bose condensates; our observations and model clarify the nature of these effective-magnetic spin rotations.

Nonmagnetic Ground State in RuO_{2} Revealed by Muon Spin Rotation.

The magnetic ground state of single crystalline RuO_{2} was investigated by the muon spin rotation and relaxation (μSR) experiment. The spin precession signal due to the spontaneous internal magnetic field B_{loc}, which is expected in the magnetically ordered phase, was not observed in the temperature range 5-400K. Muon sites were evaluated by first-principles calculations using dilute hydrogen simulating muon as pseudohydrogen, and B_{loc} was simulated for the antiferromagnetic structures with a Ru magnetic moment |m_{Ru}|≈0.05μ_{B} suggested from diffraction experiments. As a result, the possibility was ruled out that muons are localized at sites where B_{loc} accidentally cancels. Conversely, assuming that the slow relaxation observed in μSR spectra was part of the precession signal, the upper limit for the magnitude of |m_{Ru}| was estimated to be 4.8(2)×10^{-4}μ_{B}, which is significantly less than 0.05μ_{B}. These results indicate that the antiferromagnetic order, as reported, is unlikely to exist in the bulk crystal.

Producing Conventional and Transient Amino(mercapto)methyl Radicals by Addition of Muonium to a Crystalline Thioformamide (Mes*NHCH=S).

Muonium (Mu=μ+e-) is composed of a muon of light isotope of proton (μ+) and electron (e-) and can be used as a light surrogate for a hydrogen atom. In this paper, we investigated addition of muonium to a newly synthesized Mes*-substituted thioformamide (Mes*NHCH=S, Mes*=2,4,6-tBu3C6H2). Transverse-field muon spin rotation (TF-μSR) of a solution sample of the thioformamide confirmed addition of muonium to the sulfur atom leading to the corresponding C-centered radical [Mes*NHC(H)⋅-SMu]. Density functional theory (DFT) calculations assigned a conventional amino(mercapto)methyl radical, in which both nitrogen and carbon were slightly pyramidalized, and the calculated muon hyperfine coupling constant (hfcc) including the muon isotope effect was compatible with the experimentally determined parameter. However, the muon level-crossing resonance (μLCR) spectrum of an anisotropic crystalline sample indicated two paramagnetic species, and the major product showed the considerably larger muon hfcc compared with the conventional structure of the amino(mercapto)methyl radical. The unusual transient muoniated thioformamide with the larger muon hfcc that showed rapid relaxation could be only explained by a transient structure including planarization of the nitrogen and carbon atoms in Mes*NHC(H)⋅-SMu.

Exploiting Nonclassical Motion of a Trapped Ion Crystal for Quantum-Enhanced Metrology of Global and Differential Spin Rotations.

We theoretically investigate prospects for the creation of nonclassical spin states in trapped ion arrays by coupling to a squeezed state of the collective motion of the ions. The correlations of the generated spin states can be tailored for quantum-enhanced sensing of global or differential rotations of subensembles of the spins by working with specific vibrational modes of the ion array. We propose a pair of protocols to utilize the generated states and demonstrate their viability even for small systems, while assessing limitations imposed by spin-motion entanglement and technical noise. Our work suggests new opportunities for the preparation of many-body states with tailored correlations for quantum-enhanced metrology in spin-boson systems.

Symmetries and anomalies of Kitaev spin-S models: Identifying symmetry-enforced exotic quantum matter

We analyze the internal symmetries and their anomalies in the Kitaev spin-SS models. Importantly, these models have a lattice version of a \mathbb{Z}_2ℤ2 1-form symmetry, denoted by \mathbb{Z}_2^{[1]}ℤ2[1]. There is also an ordinary 0-form \mathbb{Z}_2^{(x)}×\mathbb{Z}_2^{(y)}×\mathbb{Z}_2^Tℤ2(x)×ℤ2(y)×ℤ2T symmetry, where \mathbb{Z}_2^{(x)}×\mathbb{Z}_2^{(y)}ℤ2(x)×ℤ2(y) are \piπ spin rotations around two orthogonal axes, and \mathbb{Z}_2^Tℤ2T is the time reversal symmetry. The anomalies associated with the full \mathbb{Z}_2^{(x)}×\mathbb{Z}_2^{(y)}×\mathbb{Z}_2^T×\mathbb{Z}_2^{[1]}ℤ2(x)×ℤ2(y)×ℤ2T×ℤ2[1] symmetry are classified by \mathbb{Z}_2^{17}ℤ217. We find that for S∈\mathbb{Z}S∈ℤ the model is anomaly-free, while for S∈\mathbb{Z}+\frac{1}{2}S∈ℤ+12 there is an anomaly purely associated with the 1-form symmetry, but there is no anomaly purely associated with the ordinary symmetry or mixed anomaly between the 0-form and 1-form symmetries. The consequences of these symmetries and anomalies apply to not only the Kitaev spin-SS models, but also any of their perturbed versions, assuming that the perturbations are local and respect the symmetries. If these local perturbations are weak, generically these consequences still apply even if the perturbations break the 1-form symmetry. A notable consequence is that there should generically be a deconfined fermionic excitation carrying no fractional quantum number under the \mathbb{Z}_2^{(x)}×\mathbb{Z}_2^{(y)}×\mathbb{Z}_2^Tℤ2(x)×ℤ2(y)×ℤ2T symmetry if S∈\mathbb{Z}+\frac{1}{2}S∈ℤ+12, which implies symmetry-enforced exotic quantum matter. We also discuss the consequences for S∈\mathbb{Z}S∈ℤ.

A spin–rotation mechanism of Einstein–de Haas effect based on a ferromagnetic disk

A spin–rotation mechanism of Einstein–de Haas effect based on a ferromagnetic disk

Computation of hydromagnetic tangent hyperbolic non-Newtonian flow from a rotating non-isothermal cone to a non-Darcy porous medium with thermal radiative flux

A theoretical and numerical study is conducted on nonlinear, steady-state thermal convection boundary layer flow of a magnetized incompressible Tangent Hyperbolic non-Newtonian fluid from a rotating cone to a non-Darcy porous medium. Power-law variation in temperature on the cone surface is considered and thermal radiation heat transfer is also present. The Brinkman-Darcy-Forchheimer model is deployed for the porous medium. The study is motivated by rotational (spin) coating with new emerging magnetic rheological polymers, a process which often utilizes filtration media and high temperatures. The transformed non-dimensional conservation equations are solved numerically subject to physically appropriate boundary conditions using a second-order accurate implicit finite-difference Keller Box technique. The numerical code is validated with previous studies. Extensive visualization of axial, tangential velocity components and temperature distributions with variation in key parameters including Rosseland radiative number, Darcy number, Forchheimer number (non-Darcy inertial parameter), magnetic interaction parameter, tangent-hyperbolic non-Newtonian power-law index and Weissenberg (non-Newtonian) number is included. Additionally, axial and tangential (circumferential) skin friction and Nusselt number values are tabulated for variation in key control parameters. With increasing Weissenberg number, axial velocity is depleted near the cone surface, tangential velocity is suppressed throughout the boundary layer regime and temperature is strongly enhanced. Axial flow is strongly decelerated further from the cone surface with increasing tangent-hyperbolic power-law index and there is also a significant depletion in tangential (swirl) velocity. Temperature is however boosted throughout the boundary layer transverse to the cone surface with a rise in tangent-hyperbolic power-law index. Both tangential and axial velocity are suppressed with increment in magnetic interaction parameter whereas temperature and thermal boundary layer thickness are enhanced. With larger Darcy number (i.e. greater permeability), axial velocity is strongly increased near the cone surface with no tangible modification further from the cone; However tangential velocity is consistently elevated throughout the boundary layer with greater Darcy number whereas temperature is depleted. An increase in Forchheimer number substantially damps both axial and tangential velocity whereas it elevates temperature. Increasing radiative flux strongly energizes the magnetic polymer and elevates temperature but suppresses the axial and tangential velocities. With elevation in non-isothermal wall exponent, axial skin friction is suppressed whereas Nusselt number are elevated at the cone vertex. Further along the cone surface a similar response is observed but there is also a reduction in magnitudes of tangential skin friction.

Generating a 4-photon tetrahedron state: toward simultaneous super-sensitivity to non-commuting rotations

It is often thought that the super-sensitivity of a quantum state to an observable comes at the cost of a decreased sensitivity to other non-commuting observables. For example, a squeezed state squeezed in position quadrature is super-sensitive to position displacements, but very insensitive to momentum displacements. This misconception was cleared with the introduction of the compass state [Nature 412, 712 (2001)10.1038/35089017], a quantum state equally super-sensitive to displacements in position and momentum. When looking at quantum states used to measure spin rotations, N00N states are known to be more advantageous than classical methods as long as they are aligned to the rotation axis. When considering the estimation of a rotation with unknown direction and amplitude, a certain class of states stands out with interesting properties. These states are equally sensitive to rotations around any axis, are second-order unpolarized, and can possess the rotational properties of Platonic solids in particular dimensions. Importantly, these states are optimal for simultaneously estimating the three parameters describing a rotation. In the asymptotic limit, estimating all d parameters describing a transformation simultaneously rather than sequentially can lead to a reduction of the appropriately weighted sum of the measured parameters’ variances by a factor of d. We report the experimental creation and characterization of the lowest-dimensional such state, which we call the “tetrahedron state” due to its tetrahedral symmetry. This tetrahedron state is created in the symmetric subspace of four optical photons’ polarization in a single spatial and temporal mode, which behaves as a spin-2 particle. While imperfections due to the hardware limited the performance of our method, ongoing technological advances will enable this method to generate states which out-perform any other existing strategy in per-photon comparisons.

Noncentrosymmetric Triangular Magnet CaMnTeO6: Strong Quantum Fluctuations and Role of s0 versus s2 Electronic States in Competing Exchange Interactions.

Noncentrosymmetric triangular magnets offer a unique platform for realizing strong quantum fluctuations. However, designing these quantum materials remains an open challenge attributable to a knowledge gap in the tunability of competing exchange interactions at the atomic level. Here, a new noncentrosymmetric triangular S=3/2 magnet CaMnTeO6 is created based on careful chemical and physical considerations. The model material displays competing magnetic interactions and features nonlinear optical responses with the capability of generating coherent photons. The incommensurate magnetic ground state of CaMnTeO6 with an unusually large spin rotation angle of 127°(1) indicates that the anisotropic interlayer exchange is strong and competing with the isotropic interlayer Heisenberg interaction. The moment of 1.39(1)µB, extracted from low-temperature heat capacity and neutron diffraction measurements, is only 46% of the expected value of the static moment 3µB. This reduction indicates the presence of strong quantum fluctuations in the half-integer spin S=3/2 CaMnTeO6 magnet, which is rare. By comparing the spin-polarized band structure, chemical bonding, and physical properties of AMnTeO6 (A=Ca, Sr, Pb), how quantum-chemical interpretation can illuminate insights into the fundamentals of magnetic exchange interactions, providing a powerful tool for modulating spin dynamics with atomically precise control is demonstrated.

Thermal simulations on a spinning rotor gauge to improve systematic uncertainties for viscosity measurements

Experimental values for the viscosity of the radioactive hydrogen isotope tritium (T2) are currently unavailable in literature. The value of this material property over a wide temperature range is of interest for applications in the field of fusion, neutrino physics, as well as to test ab initio calculations. To measure the viscosity of tritium, a measurement setup has been built utilizing a spinning rotor gauge inside a Dewar. Temperature control is of high importance to produce accurate and precise values. To ensure high quality measurement results, prior to the tritium measurements, thermal simulations are done on measurements with protium and deuterium inside the sample gas volume of the spinning rotor gauge.

Persistent spin texture in ferroelectric Hf0.5Zr0.5O2

Persistent spin texture (PST) refers to the unidirectional spin configuration in momentum space and preserves the SU(2) spin rotation symmetry, which protects the spin coherence against the relaxation and renders an ultimately infinite spin lifetime. In this regard, it would be desirable to find high-quality quantum materials sustaining the intrinsic PST. Here, based on density-functional theory calculations, we show that the ferroelectric Hf0.5Zr0.5O2 sustains a PST over large area of Brillouin zone around the conduction band minimum, while the Rashba-type spin texture dominates around the valence band maximum. Based on the group-theoretical analysis, we construct an effective k·p Hamiltonian model and demonstrate that the PST arises from the significant anisotropy of spin splitting, which pins the spin–orbit field to certain direction. In addition, we elucidate the spin SU(2) symmetry for the discovered PST. Given the fact that Hf0.5Zr0.5O2 is compatible with silicon semiconductor technologies, our work discovers a high-quality oxide material sustaining the PST, which holds great promise for spin-orbitronic applications.

Rotational photonic spin Hall effect on twisted bilayer metasurfaces

Optical differential operations possess the remarkable advantages of high efficiency and real-time imaging, which can improve the ability of image processing to enhance image edge detection. The photonic spin Hall effect has been demonstrated to realize optical differential operations. However, the direction of optical differential operation generated by the conventional photonic spin Hall effect is single and fixed. Here, we propose a scheme for the rotational photonic spin Hall effect on twisted bilayer metasurfaces to obtain the optical differential operations in any desirable directions and phase reconstruction. The rotation angle of the rotational photonic spin Hall effect is defined as the tangent of the in-plane spin-dependent shift to the transverse spin-dependent shift. The twist angle of the bilayer metasurfaces influence the Fresnel reflection coefficients which affect the transverse spin-dependent shift and the in-plane spin-dependent shift. Therefore, the direction of rotational photonic spin Hall effect can be controlled by the twist angle of the bilayer metasurfaces. Moreover, we show applications of the rotational photonic spin Hall effect including image edge detection and phase reconstruction. These findings open up new horizons for future applications of the rotational photonic spin Hall effect in optics.

Fabrication of single-crystalline YFeO3 films with large antiferromagnetic domains

The antiferromagnetic orthoferrite YFeO3 possesses fascinating magnetic properties for spintronics, such as terahertz spin dynamics, ultrafast domain wall motion, and long magnon decay length. YFeO3 belongs to a special family of antiferromagnets that show an unusually strong non-trivial Kerr response due to its weak ferromagnetism. The highly stable antiferromagnetic domains without any spontaneous spin rotation transitions below the 645 K Néel temperature may be useful for nanoscale device applications. We report the successful fabrication of high-quality twinning-free (110)-oriented YFeO3 films by pulsed laser deposition. Detailed structural and magnetic characterization revealed that the crystal structure and magnetic properties of the YFeO3 films are comparable to bulk single crystals. We show that the spin rotation under high magnetic fields follows the two-sublattice approximation model. The film surface is atomically flat with step-terrace surface morphology. A longitudinal magneto-optic Kerr (MOKE) rotation of 10 mdeg was observed at room temperature, which is consistent with earlier reports on bulk single crystals. The in-plane anisotropy of the Kerr response corresponds to the obtained magnetic anisotropy from the SQUID measurement. The large MOKE signal enables the imaging of antiferromagnetic domains and their reversal. The domain size was found to be larger than 100 μm. These high-quality YFeO3 thin films facilitate the fabrication of antiferromagnetic spintronic devices and provide a convenient platform for studying various spin-related phenomena in thin films and at interfaces.