Spin Dependence Research Articles

Direct detection of spin-dependent sub-GeV dark matter via Migdal effect

Motivated by the current strong constraints on the spin-independent dark matter (DM)-nucleus scattering, we investigate the spin-dependent (SD) interactions of the light Majorana DM with the nucleus mediated by an axial-vector boson. Due to the small nucleus recoil energy, the ionization signals have now been used to probe the light dark matter particles in direct detection experiments. With the existing ionization data, we derive the exclusion limits on the SD DM-nucleus scattering through Migdal effect in the MeV-GeV DM mass range. It is found that the lower limit of the DM mass can reach about several MeVs. Due to the momentum transfer correction induced by the light mediator, the bounds on the SD DM-nucleus scattering cross sections can be weakened in comparison with the heavy mediator.

Nuclear collective motion of heavy nuclei with axial quadrupole and octupole deformation

A quadrupole-octupole axially symmetric model is constructed for the unified description of alternate parity bands corresponding to octupole vibration or a stable deformation. The model depends on two parameters whose clear physical meaning allows a systematic description of the rotation-vibration dynamics of alternate parity bands analyzed for isotopic sequences of Ra, Th, U, and Pu nuclei. A critical point is identified in the $A=224--228$ mass region of the Ra and Th nuclei marking different stages of the transition between static and dynamic octupole deformation. Model predictions are performed for energies of unobserved states of the yrast sequence and of the excited bands as well as for the $E1, E2$, and $E3$ transition rates, which reproduce the available experimental data and exhibit a specific spin dependence for the transitional nuclei.

π-Stacked (Cn-C6H6–Fe–C6H6–C13-n)n=2: A spin operated thermoelectric nanodevice

Harvesting waste heat back into electricity by exploiting the temperature difference across two ends of a nanodevice and its concomitant spin dependence has led to the emergence of a new field known as spin caloritronics. Herein, we report the spin polarized thermoelectric features in a π-stacked system comprised of (Cn-C6H6–Fe–C6H6–C13-n)n = 2. A decisive factor, the Seebeck coefficient, becomes fully spin dependent on temperature and switches from positive to negative values, which illustrates the switching of the thermoelectric behavior from a p-to n-type due to the change in the spin state from spin-down to spin-up. A relatively large thermoelectric figure of merit has been reported in the case of the spin figure of merit of the system. In this context, three major observations have been made: i) The Seebeck coefficient has a distinctive feature over two different spin channels, ii) the spin Seebeck coefficient (Ss) is nearly four times larger than the charge Seebeck coefficient (Sc), and (iii) the spin thermoelectric figure of merit (ZS) rises by 80% with respect to charge thermoelectric figure of merit (ZC) under thermal bias. Our results have been well explained through the analysis of temperature dependent transmission spectra of the system. The emergence of a relatively large spin Seebeck coefficient allows us to measure the pure spin current of the system as well as extending the devices application from simple memory (MRAM) devices to on-chip energy harvesting systems.

Thermodynamic and dynamical signatures of a quantum spin Hall insulator to superconductor transition

Thermodynamic and dynamical properties of a model of Dirac fermions with a deconfined quantum critical point (DQCP) separating an interaction-generated quantum spin-Hall insulator from an s-wave superconductor [Nature Comm.~{\bf 10}, 2658 (2019)] are studied by quantum Monte Carlo simulations. Inside the deconfined quantum critical region bound by the single-particle gap, spinons and spinless charge-2e skyrmions emerge. Since the model conserves total spin and charge, and has a single length scale, these excitations lead to a characteristic linear temperature dependence of the uniform spin and charge susceptibilities. At the DQCP, the order parameter dynamic structure factors show remarkable similarities that support emergent Lorentz symmetry. Above a critical temperature, superconductivity is destroyed by the proliferation of spin-1/2 vortices.

Searching conformational analysis of Asp residues through theoretical 3J vicinal coupling constants and Karplus equations

AbstractThe dependence of the vicinal spin–spin coupling constants on the torsion side chain angle χ1 through the Karplus equations is considered for the study of the structure of Asp amino acid residues. Experimental and theoretical, obtained with density functional theory methods, vicinal coupling constants combined with extended Karplus equations, which include six coefficients, are applied to a dipeptide model of the amino acid Asp. To find out the empirical χ1 angles of the side chain, a statistical analysis procedure is developed to compute the rmsd values and find the χ1 as the minimum of those values. The χ1 values obtained in this work for nine Asp residues of the flavodoxin protein Desulfovibrio vulgaris are successfully compared with those derived by nuclear magnetic resonance and X‐rays.

The NICA-SPD project: a new tool to investigate the hadron structure

SPD is an international Collaboration gathering around the Spin Physics Detector at the Nuclotron-based Ion Collider FAcility (NICA), presently under construction at the Joint Institute per Nuclear Research, in Dubna. The project is briefly presented with special focus to the opportunities opened by the collision of high luminosity polarized proton and deuteron beams with total energy up to $\sqrt{s}$=27 GeV. Examples of the foreseen research program are highlighted, in connection with the spin structure of light nuclei, the proton gluon content and the spin dependence of the nucleon-nucleon interaction. The unicity of NICA-SPD makes the future results complementary to the studies that have been or will be performed at other polarized hadron machines in different energy domains.

On the conformal spin dependence of the perturbative QCD vacuum singularity

We study the four-gluon scattering amplitude in the high energy limit of QCD written in terms of its conformal expansion. We highlight the need to include both even and odd conformal spin contributions in order to map it to an iterative representation in rapidity and transverse momentum space which we have evaluated numerically. By Fourier expanding in a set of three azimuthal angles, we find a new form for the amplitude in terms of 4F3 hypergeometric functions. An alternative formulation is possible when connecting this Fourier expansion with Bessel kernels studied in analytic number theory.

Method for the definitive detection of orbital angular momentum states in neutrons by spin-polarized 3He.

A standard method to detect thermal neutrons is the nuclear interaction 3He(n,p)3H. The spin dependence of this interaction is also the basis of a neutron spin-polarization filter using nuclear polarized 3He. We consider the corresponding interaction for neutrons placed in an intrinsic orbital angular momentum (OAM) state. We derive the relative polarization-dependent absorption cross sections for neutrons in an OAM state. The absorption of those neutrons results in compound states , , and . Varying the three available polarizations tests that an OAM neutron has been absorbed and probes which decay states are physically possible. We describe the energetically likely excited states of 4He after absorption, taking account of the odd parity of the compound state. This provides a definitive method for detecting neutron OAM states and suggests that intrinsic OAM states offer the possibility to observe new physics, including anomalous cross sections and new channels of radioactive decay.

Spin-Dependent Scattering of Scalar and Vector Dark Matter on the Electron

The property of dark matter remains to date unknown. However, a model-independent classification of dark matter candidates can be achieved by using various symmetries, as performed in the standard model. Fermionic dark matter has been extensively researched, and one favored candidate is the neutralino in the Minimal Supersymmetric Standard Model, which is required by fermion–boson symmetry and the preservation of R-parity. Bosonic dark matter has not been sufficiently studied, especially the scenario of dark matter with a mass of sub-GeV. In this paper, we consider the effect of spin-dependent (SD) on scalar and vector dark matter, which are mediated by pseudoscalar and axial-vector, and evaluate the effect on the dark matter–electron scattering cross-section. We list all the interactions and form factor of dark matter–electron SD scattering, and use XENON10/100/1T experiment data to derive the exclusion limit of the SD cross-section. We find that the SD scattering of scalar and vector dark matter can be three orders of magnitude stronger than spin-independent (SI) scattering due to the p-wave scattering.

Molecular motion of imidazolium cations and phase transitions in (ImH)2KCo(CN)6 with double perovskite structure

Temperature dependence of 1H nuclear magnetic resonance spin–lattice relaxation time T1 of (ImH)2KCo(CN)6, ImH+: imidazolium cation, is reported. The asymmetric T1 minimum observed in intermediate-temperature phase between 198 and 112 K is analyzed assuming the Cole-Davidson distribution of correlation time. Temperature dependences of 14N nuclear quadrupole resonance frequencies and spin–lattice relaxation times are also reported. The phase transitions at 198 and 112 K are shown to be of second and first order, respectively. The 14N relaxation is shown to be governed by the electric field gradient fluctuation due to the in-plane reorientational motion of the imidazolium cations.

Motion of spinning particles around electrically charged black hole in Eddington-inspired Born–Infeld gravity

A test particle possessing spin angular momentum moves along a non-geodesic path due to an additional spin-curvature force. We study the spinning test particle moving in the vicinity of the electrically charged black hole formation in Eddington-inspired Born–Infeld (EiBI) gravity. Through the numerical analysis of its effective potential and orbits, it is found that the orbital eccentricity reduces as the deviation parameter kappa increases. By comparing the orbits for the observed stars around Sagittarius A*, we conclude that the observed orbits with too large radii can not give a stringent constraint with acceptable magnitude. To dig out the potential observation effects of the relations between the orbits and parameter kappa , we mainly focus on the orbits in the vicinity of black hole in this paper. The parameters of inner most stable circular orbit (ISCO) decrease monotonously with kappa when the spin angular momentum is small, however they change non-monotonously with kappa when the spin is large enough. Moreover, the spin dependences of ISCO parameters have similar behavior to that of Reissner–Nordström (RN) black hole. We analyze the causality of the circular orbits by using the superluminal constraint condition as well. As a result, two new parameter regions may emerge in case of large kappa , where the particle has two stable circular orbits with one subluminal and the other superluminal.

Spontaneous fission hindrance in even-odd nuclei within a cluster approach

For even-odd isotopes of actinides and superheavy nuclei, spontaneous fission and $\ensuremath{\alpha}$-decay half-lives are calculated within the dinuclear system model and compared with the existing experimental data. All these processes are considered as the evolution of a nucleus in the charge (mass) asymmetry coordinate and in the relative distance between the centers of clusters formed. The important role of the spin dependence of total potential energy in the charge asymmetry coordinate is shown and the origin of the fission hindrance in even-odd nuclei is explained.

Thickness dependence of spin–orbit torques in Pt/Co structures on epitaxial substrates

We investigate the Pt thickness dependence of spin–orbit torques (SOTs) in Co/Pt layers grown on single crystalline SrTiO3 and LaAlO3 and amorphous SiO2 substrates. We measure the SOT-induced effective damping-like fields and spin Hall magnetoresistances of the Co/Pt (tPt) samples, where tPt varies from 0.5 to 5.5 nm. We find that the Co/Pt layers grown on the single crystalline substrates show weaker thickness dependence of the SOT than the samples on the SiO2 substrate, which cannot be explained by the conventional bulk spin Hall effect in the Pt layer. This indicates that there is a non-negligible interfacial SOT originating from the Pt/substrate interface, which is more pronounced for thinner Pt. These results provide a way to design SOT material structures with enhanced SOT efficiency by incorporating interfacial SOT.

The thickness dependence of the field-like spin–orbit torque in heavy metal/CoFeB/MgO heterostructures

We investigated the ferromagnet (FM) and heavy metal (HM) thickness dependence of the electric current-induced spin orbit torque (SOT), especially the field-like (FL) torque component in HM/CoFeB/MgO heterostructures. For Pt/CoFeB/MgO and Ta/CoFeB/MgO structures, after subtracting the dead-layer thickness of CoFeB, the damping-like (DL) effective field follows 1/tFM dependence, while the FL effective field deviates from 1/tFM dependence at the ultra-thin FM thickness range, indicating that an extra origination of FL torque, i.e., spin backflow at the FM/MgO interface, is responsible for the large FL torque in HM/CoFeB/MgO structures with a ultra-thin CoFeB layer. For Ta/Pt(tPt)/CoFeB(1)/MgO structures, the FL-SOT exhibits a gradual change similar to the DL-SOT, suggesting that the spin Hall effect is the dominant origination of spin current, which enhances the FL-SOT in the HM/CoFeB/MgO structures by the spin backflow effect when tCoFeB is less than the spin dephasing length. We also demonstrated that the obvious dead-layer thickness at the Ta/CoFeB interface reduces the effective CoFeB thickness and enhances the spin backflow effect further.

Possible Studies at the First Stage of the NICA Collider Operation with Polarized and Unpolarized Proton and Deuteron Beams

This paper contains suggestions for experiments with usage of the Spin Physics Detector (SPD) at the first stage of the SPD NICA Programme developing at JINR. Double polarized pp-, dd- and pd- collisions at c.m.s. NN energies of 3.4-10 GeV, which will be accessible at the initial stage of experiments, allow one to study spin dependence of the NN interaction, search for multiquark states at double strangeness, charm and beauty thresholds, study the short-range structure of the deuteron. Double polarized pd scattering offer a possibility to test the Standard Model through the search for T-invariance violation.

Magnetic moment predictions of odd-A nuclei with the Bayesian neural network approach * *Supported by the National Natural Science Foundation of China (11675063, 11875070, 11205068) and the Open fund for Discipline Construction, Institute of Physical Science and Information Technology, Anhui University

The Bayesian neural network approach has been employed to improve the nuclear magnetic moment predictions of odd-A nuclei. The Schmidt magnetic moment obtained from the extreme single-particle shell model makes large root-mean-square (rms) deviations from data, i.e., 0.949 and 1.272 for odd-neutron nuclei and odd-proton nuclei, respectively. By including the dependence of the nuclear spin and Schmidt magnetic moment, the machine-learning approach precisely describes the magnetic moments of odd-A nuclei with rms deviations of 0.036 for odd-neutron nuclei and 0.061 for odd-proton nuclei. Furthermore, the evolution of magnetic moments along isotopic chains, including the staggering and sudden jump trend, which are difficult to describe using nuclear models, have been well reproduced by the Bayesian neural network (BNN) approach. The magnetic moments of doubly closed-shell nuclei, for example, isoscalar and isovector magnetic moments, have been well studied and compared with the corresponding non-relativistic and relativistic calculations.

Dynamical preparation of stripe states in spin-orbit-coupled gases

In spinor Bose-Einstein condensates, spin-changing collisions are a remarkable proxy to coherently realize macroscopic many-body quantum states. These processes have been, e.g., exploited to generate entanglement, to study dynamical quantum phase transitions, and proposed for realizing nematic phases in atomic condensates. In the same systems dressed by Raman beams, the coupling between spin and momentum induces a spin dependence in the scattering processes taking place in the gas. Here we show that, at weak couplings, such modulation of the collisions leads to an effective Hamiltonian which is equivalent to the one of an artificial spinor gas with spin-changing collisions that are tunable with the Raman intensity. By exploiting this dressed-basis description, we propose a robust protocol to coherently drive the spin-orbit coupled condensate into the ferromagnetic stripe phase via crossing a quantum phase transition of the effective low-energy model in an excited-state.

The SAMI Galaxy Survey: Detection of Environmental Dependence of Galaxy Spin in Observations and Simulations Using Marked Correlation Functions

Abstract The existence of a kinematic morphology–density relation remains uncertain, and instead stellar mass appears the more dominant driver of galaxy kinematics. We investigate the dependence of the stellar spin parameter proxy λ R e on environment using a marked cross-correlation method with data from the Sydney Australian Astronomical Observatory Multi-object Integral-field Spectrograph (SAMI) Galaxy Survey. Our sample contains 710 galaxies with spatially resolved stellar velocity and velocity dispersion measurements. By utilizing the highly complete spectroscopic data from the Galaxy and Mass Assembly Survey, we calculate marked cross-correlation functions for SAMI galaxies using a pair count estimator and marks based on stellar mass and λ R e . We detect an anticorrelation of stellar kinematics with environment at the 3.2σ level, such that galaxies with low λ R e values are preferably located in denser galaxy environments. However, a significant correlation between stellar mass and environment is also found (correlation at 2.4σ), as found in previous works. We compare these results to mock observations from the cosmological Evolution and Assembly of Galaxies and their Environments (EAGLE) simulations, where we find a similar significant λ R e anticorrelation with environment, and a mass and environment correlation. We demonstrate that the environmental correlation of λ R e is not caused by the mass–environment relation. The significant relationship between λ R e and environment remains when we exclude slow rotators. The signals in SAMI and EAGLE are strongest on small scales (10–100 kpc) as expected from galaxy interactions and mergers. Our work demonstrates that the technique of marked correlation functions is an effective tool for detecting the relationship between λ R e and environment.

Ion beam etching dependence of spin–orbit torque memory devices with switching current densities reduced by Hf interlayers

We report on the fabrication of nanoscale, three-terminal in-plane spin–orbit torque switching devices with low switching current densities. Critical parameters in the fabrication process, including the ion beam etching angle and time, were optimized to avoid fabrication defects and improve device yield. Measurements of the magnetic field and current-induced switching behavior of the tunnel junctions demonstrate a sensitivity to the nanopillar aspect ratio, which dictates the nanopillars’ anisotropy and thermal stability. Additionally, we show that the current density required for switching can be reduced and the device thermal stability increased by inserting Hf interlayers into the heterostructure. Micromagnetic simulations are generally consistent with the experimentally observed switching behavior, suggesting an increase in the interfacial perpendicular anisotropy at the CoFeB/MgO interface and the reduction in the Dzyaloshinskii–Moriya interaction at the W/CoFeB interface by the Hf interlayers.

Evidence for new enantiospecific interaction force in chiral biomolecules

Evidence for new enantiospecific interaction force in chiral biomolecules