Opposite Spin Components Research Articles

Polarization dynamics in the paramagnet of a charged quark-gluon plasma

It is commonly understood that the strong magnetic field produced in heavy ion collisions is short-lived. The electric conductivity of the quark-gluon plasma is unable to significantly extend the lifetime of the magnetic field. We propose an alternative scenario to achieve this: with finite baryon density and spin polarization by the initial magnetic field, the quark-gluon plasma behaves as a paramagnet, which may continue to polarize the quark after fading of the initial magnetic field. We confirm this picture by calculations in both quantum electrodynamics and quantum chromodynamics. In the former case, we find a splitting in the damping rates of probe fermions with an opposite spin component along the magnetic field. In the latter case, we find a similar splitting in damping rate of the probe quark in quark-gluon plasma in both high and low density limits. The splitting provides a way of polarizing strange quarks by the quark-gluon plasma paramagnet consisting of light quarks, which effectively extends the lifetime of the magnetic field in heavy ion collisions. Published by the American Physical Society 2024

Electrically triggered spin reversal and precise control of spin polarization for electron transport at the single-molecule level

Different from conventional ferromagnetic methods, producing a spin-polarized current through electrical ways in spintronic devices can greatly increase operating speed, reduce power consumption, and improve device integration. Inspired by recent experimental progress on the synthesis of a heptauthrene molecule, we investigate its spin-dependent transport contacted with Au electrodes through first-principles calculations. By applying a gate voltage, the transmission can be switched between completely spin-up and spin-down polarized states, achieving an electrically controlled dual-spin filter. Furthermore, a fine tuning on the spin polarization, between 100% and −100%, can also be realized, where the transport with any ratio of spin-up to spin-down electron quantities can be realized beyond the traditional devices. The peculiar transmission spectra and their shift are found to play crucial roles, where transmission peaks distribute on both sides of the Fermi level with opposite spin components. Such a spin-polarization modulating effect is found to be robust to the molecule-electrode contacting site, indicating it is an intrinsic feature of such systems. Moreover, the dimension of the device is at the single-molecule level, suggesting great application potential.

Plasmonic metasurfaces manipulating the two spin components from spin–orbit interactions of light with lattice field generations

Abstract Artificial nanostructures in metasurfaces induce strong spin–orbit interactions (SOIs), by which incident circularly polarized light can be transformed into two opposite spin components. The component with an opposite helicity to the incident light acquires a geometric phase and is used to realize the versatile functions of the metasurfaces; however, the other component, with an identical helicity, is often neglected as a diffused background. Here, by simultaneously manipulating the two spin components originating from the SOI in plasmonic metasurfaces, independent wavefields in the primary and converted spin channels are achieved; the wavefield in the primary channel is controlled by tailoring the dynamic phase, and that in the converted channel is regulated by designing the Pancharatnam–Berry phase in concurrence with the dynamic phase. The scheme is realized by generating optical lattice fields with different topologies in two spin channels, with the metasurfaces composed of metal nanoslits within six round-apertures mimicking the multi-beam interference. This study demonstrates independent optical fields in a dual-spin channel based on the SOI effect in the metasurface, which provides a higher polarization degree of freedom to modify optical properties at the subwavelength scale.

Two-body mobility edge in the Anderson-Hubbard model in three dimensions: Molecular versus scattering states

Most of our quantitative understanding of disorder-induced metal-insulator transitions comes from numerical studies of simple noninteracting tight-binding models, like the Anderson model in three dimensions. An important outstanding problem is the fate of the Anderson transition in the presence of additional Hubbard interactions of strength $U$ between particles. Based on large-scale numerics, we compute the position of the mobility edge for a system of two identical bosons or two fermions with opposite spin components. The resulting phase diagram in the interaction-energy-disorder space possesses a remarkably rich and counterintuitive structure, with multiple metallic and insulating phases. We show that this phenomenon originates from the molecular or scattering-like nature of the pair states available at given energy $E$ and disorder strength $W$. The disorder-averaged density of states of the effective model for the pair is also investigated. Finally, we discuss the implications of our results for ongoing research on many-body localization.

Black phosphorus terahertz sensing based on photonic spin Hall effect.

A novel terahertz (THz) sensing scheme is proposed based on the photonic spin Hall effect (PSHE). By illumining a paraxial Gaussian THz beam onto a black phosphorus (BP)-based Tamm structure, the reflected beam will undergo in-plane spin splitting, i.e., the centroids of two opposite spin components separate spatially. Due to Tamm plasmon resonance, one of the spin components is very sensitive to the refractive index changes of the analyte layer sandwiched by monolayer BP and distributed Bragg reflector. The sensitivity of the spin-dependent shift can be up to 2804 mm/RIU with a refractive index resolution of ∼10-8 RIU. The sensitivity and dynamic sensing region can be flexibly tuned by the BP rotation angle, thickness of analyte layer, or operation frequency. Therefore, the proposed PSHE-based THz sensing provides a new avenue for the development of high-performance THz sensors; thus, we may find applications in chemical sensing and biosensing.

Probing nanoscale fluctuation of ferromagnetic meta-atoms with a stochastic photonic spin Hall effect.

The photonic spin Hall effect, a deep subdiffraction-limited shift between the opposite spin components of light, emerges when light undergoes an evolution of polarization or trajectory that induces the geometric phase. Here, we study a stochastic photonic spin Hall effect arising from space-variant Berry-Zak phases, which are generated by disordered magneto-optical effects. This spin shift is observed from a spatially bounded lattice of ferromagnetic meta-atoms displaying nanoscale disorders. A random variation of the radii of the meta-atoms induces the nanoscale fluctuation. The standard deviation of the probability distribution of the spin shifts is proportional to the fluctuation of the meta-atoms. This enables us to detect a five-nanometre fluctuation by measuring the probability distribution of the spin shifts via weak measurements. Our approach may be used for sensing deep-subwavelength disorders by actively breaking the photonic spin symmetry and may enable investigations of fluctuation effects in magnetic nanosystems.

Q-MP2-OS: Møller-Plesset Correlation Energy by Quadrature.

We present a quadrature-based algorithm for computing the opposite-spin component of the MP2 correlation energy which scales quadratically with basis set size and is well-suited to large-scale parallelization. The key ideas, which are rooted in the earlier work of Hirata and co-workers, are to abandon all two-electron integrals, recast the energy as a seven-dimensional integral, approximate that integral by quadrature, and employ a cutoff strategy to minimize the number of intermediate quantities. We discuss our implementation in detail and show that it parallelizes almost perfectly on 840 cores for cyclosporine (a molecule with roughly 200 atoms), exhibits [Formula: see text] scaling for a sequence of polyglycines, and is principally limited by the accuracy of its quadrature.

Photonic spin Hall effect of monolayer black phosphorus in the Terahertz region

Abstract As a two-dimensional (2D) material, black phosphorus (BP) has attracted significant attention owing to exotic physical properties such as low-energy band gap, high carrier mobility, and strong in-plane anisotropy. The striking in-plane anisotropy is a promising candidate for novel light-matter interaction. Here, we investigate the photonic spin Hall effect (PSHE) on a monolayer of BP. Due to the in-plane anisotropic property of BP, the PSHE is accompanied with Goos-Hänchen and Imbert-Fedorov effects, resulting in an asymmetric spin splitting. The asymmetric spin splitting can be flexibly tuned by the angle between the incident plane and the armchair crystalline direction of BP and by the carrier density via a bias voltage. The centroid displacements of two opposite spin components of the reflected beam along directions parallel and perpendicular to the incident plane can be considered as four independent channels for information processing. The potential application in barcode-encryption is proposed and discussed. These findings provide a deeper insight into the spin-orbit interaction in 2D material and thereby facilitate the development of optoelectronic devices in the Terahertz region.

Generalized spin-ratio scaled MP2 method for accurate prediction of intermolecular interactions for neutral and ionic species.

The accurate calculation of intermolecular interactions is important to our understanding of properties in large molecular systems. The high computational cost of the current "gold standard" method, coupled cluster with singles and doubles and perturbative triples (CCSD(T), limits its application to small- to medium-sized systems. Second-order Møller-Plesset perturbation (MP2) theory is a cheaper alternative for larger systems, although at the expense of its decreased accuracy, especially when treating van der Waals complexes. In this study, a new modification of the spin-component scaled MP2 method was proposed for a wide range of intermolecular complexes including two well-known datasets, S22 and S66, and a large dataset of ionic liquids consisting of 174 single ion pairs, IL174. It was found that the spin ratio, ϵΔs=EINTOSEINTSS, calculated as the ratio of the opposite-spin component to the same-spin component of the interaction correlation energy fell in the range of 0.1 and 1.6, in contrast to the range of 3-4 usually observed for the ratio of absolute correlation energy, ϵs=EOSESS, in individual molecules. Scaled coefficients were found to become negative when the spin ratio fell in close proximity to 1.0, and therefore, the studied intermolecular complexes were divided into two groups: (1) complexes with ϵΔs< 1 and (2) complexes with ϵΔs≥ 1. A separate set of coefficients was obtained for both groups. Exclusion of counterpoise correction during scaling was found to produce superior results due to decreased error. Among a series of Dunning's basis sets, cc-pVTZ and cc-pVQZ were found to be the best performing ones, with a mean absolute error of 1.4 kJ mol-1 and maximum errors below 6.2 kJ mol-1. The new modification, spin-ratio scaled second-order Møller-Plesset perturbation, treats both dispersion-driven and hydrogen-bonded complexes equally well, thus validating its robustness with respect to the interaction type ranging from ionic to neutral species at minimal computational cost.

New SCS- and SOS-MP2 Coefficients Fitted to Semi-Coulombic Systems.

Spin-component scaled second-order Møller-Plesset perturbation theory (SCS-MP2) energy calculations, which independently scale the opposite- and same-spin components of the MP2 correlation energy, are known to consistently provide improved interaction energies in comparison to conventional MP2. This has led to the development of a number of SCS-MP2 derivatives that target particular classes of molecules, interactions or properties. In this study, SCS-MP2 scaling coefficients targeted to interaction energies of single ion pair semi-Coulombic ionic liquid (IL) systems are presented in view of circumventing the need for counterpoise correction to eliminate basis set superposition error (BSSE). A set of 174 IL ion pairs consisting of imidazolium ([C(1-4)mim](+)) and pyrrolidinium ([C(1-4)mpyr](+)) cations and routinely used anions such as Br(-), Cl(-), [BF4](-), [PF6](-), [DCA](-) (dicyanamide), [tos](-) (tosylate), [mes](-) (mesylate), and [NTf2](-) (bis(trifluoromethylsulfonyl)amide), each of which were arranged in multiple favorable conformations, were calculated at the MP2 level of theory with 17 popular basis sets ranging from double- to quadruple-ζ quality and at the CCSD(T)/CBS limit. For each basis set, the spin components of the IL set were scaled via least-squares multiple linear regression with respect to CCSD(T)/CBS benchmark interaction energies that were corrected for BSSE using the Boys and Bernardi approach. SCS-MP2 spin component coefficients of 1.05 and 0.68 are recommended for the opposite- and same-spin components, respectively, in conjunction with Dunning's cc-pVTZ basis set, which resulted in the most statistically reliable regression. Alternatively, a scaled opposite-spin MP2 (SOS-MP2) scaling factors of 1.64 is recommended for the opposite-spin component and should be used where the omission of the same-spin component results in a calculation speed-up. These two scaling schemes are termed SCS-IL-MP2 and SOS-IL-MP2, respectively. The SCS-IL-MP2 and SOS-IL-MP2 approaches show interaction energy errors on average less than 1.0 kJ mol(-1) with respect to CCSD(T)/CBS benchmark results and highlights the important consideration of basis set dependence when selecting spin-component coefficients. By calculating multiple conformations for each ion pair and scaling to reproduce BSSE corrected benchmark energies, it is suggested that improved energies may be obtained for larger IL clusters beyond ion pairs without performing costly counterpoise corrections.

Counterrotating stars in simulated galaxy discs

Counterrotating stars in disk galaxies are a puzzling dynamical feature whose origin has been ascribed to either satellite accretion events or to disk instabilities triggered by deviations from axisymmetry. We use a cosmological simulation of the formation of a disk galaxy to show that counterrotating stellar disk components may arise naturally in hierarchically-clustering scenarios even in the absence of merging. The simulated disk galaxy consists of two coplanar, overlapping stellar components with opposite spins: an inner counterrotating bar-like structure made up mostly of old stars surrounded by an extended, rotationally-supported disk of younger stars. The opposite-spin components originate from material accreted from two distinct filamentary structures which at turn around, when their net spin is acquired, intersect delineating a "V"-like structure. Each filament torques the other in opposite directions; the filament that first drains into the galaxy forms the inner counterrotating bar, while material accreted from the other filament forms the outer disk. Mergers do not play a substantial role and most stars in the galaxy are formed in situ; only 9% of all stars are contributed by accretion events. The formation scenario we describe here implies a significant age difference between the co- and counterrotating components, which may be used to discriminate between competing scenarios for the origin of counterrotating stars in disk galaxies.

Triplet order parameter component at Co/CoO/In contacts

We show measurements of the dynamical conductance of a device consisting of thin ferromagnetic cobalt strips having alternating stronger and weaker coercive fields, located less than a coherence length apart connecting two superconducting indium electrodes. At a bias lower than the superconducting gap the conductance is sensitive to the relative polarization of adjacent ferromagnetic strips. We find that the conductance is higher when the wire polarizations are parallel. The sign and magnitude of this effect are interpreted in terms of the balance between equal and opposite spin components of the superconducting order parameters at the interface.

Spin drag in a perfect fluid

Beautiful experiments in an ultracold, strongly interacting atomic Fermi gas reveal that, unexpectedly, unpaired atomic spins flow in the system with the maximum resistance permitted by the laws of quantum mechanics. See Letter p.201 Strongly interacting Fermi gases are ubiquitous in nature, from electrons in high-temperature superconductors, to nuclear matter. Their transport properties, such as the speed of diffusion, are poorly understood. Sommer et al. use controlled collisions of ultracold atomic clouds to investigate spin transport in a strongly interacting Fermi gas. They find that the spin excitations are maximally damped (leading to high spin drag), and that interactions are strong enough to reverse spin currents so that opposite spin components reflect off each other. The speed of diffusion is set by a fundamental quantum limit. The results have implications for any area involving fermion transport, from spintronics to studies of the early Universe.

Universal spin transport in a strongly interacting Fermi gas

Transport of fermions, particles with half-integer spin, is central to many fields of physics. Electron transport runs modern technology, defining states of matter such as superconductors and insulators, and electron spin is being explored as a new carrier of information. Neutrino transport energizes supernova explosions following the collapse of a dying star, and hydrodynamic transport of the quark-gluon plasma governed the expansion of the early Universe. However, our understanding of non-equilibrium dynamics in such strongly interacting fermionic matter is still limited. Ultracold gases of fermionic atoms realize a pristine model for such systems and can be studied in real time with the precision of atomic physics. Even above the superfluid transition, such gases flow as an almost perfect fluid with very low viscosity when interactions are tuned to a scattering resonance. In this hydrodynamic regime, collective density excitations are weakly damped. Here we experimentally investigate spin excitations in a Fermi gas of (6)Li atoms, finding that, in contrast, they are maximally damped. A spin current is induced by spatially separating two spin components and observing their evolution in an external trapping potential. We demonstrate that interactions can be strong enough to reverse spin currents, with components of opposite spin reflecting off each other. Near equilibrium, we obtain the spin drag coefficient, the spin diffusivity and the spin susceptibility as a function of temperature on resonance and show that they obey universal laws at high temperatures. In the degenerate regime, the spin diffusivity approaches a value set by [planck]/m, the quantum limit of diffusion, where [planck]/m is Planck's constant divided by 2π and m the atomic mass. For repulsive interactions, our measurements seem to exclude a metastable ferromagnetic state.

Improvement of the coupled-cluster singles and doubles method via scaling same- and opposite-spin components of the double excitation correlation energy

There has been much interest in cost-free improvements to second-order Møller-Plesset perturbation theory (MP2) via scaling the same- and opposite-spin components of the correlation energy (spin-component scaled MP2). By scaling the same- and opposite-spin components of the double excitation correlation energy from the coupled-cluster of single and double excitations (CCSD) method, similar improvements can be achieved. Optimized for a set of 48 reaction energies, scaling factors were determined to be 1.13 and 1.27 for the same- and opposite-spin components, respectively. Preliminary results suggest that the spin-component scaled CCSD (SCS-CCSD) method will outperform all MP2 type methods considered for describing intermolecular interactions. Potential energy curves computed with the SCS-CCSD method for the sandwich benzene dimer and methane dimer reproduce the benchmark CCSD(T) potential curves with errors of only a few hundredths of 1 kcal mol(-1) for the minima. The performance of the SCS-CCSD method suggests that it is a reliable, lower cost alternative to the CCSD(T) method.

Orbital-optimized opposite-spin scaled second-order correlation: An economical method to improve the description of open-shell molecules

Coupled-cluster methods based on Brueckner orbitals are well known to resolve the problems of symmetry breaking and spin contamination that are often associated with Hartree-Fock orbitals. However, their computational cost is large enough to prevent application to large molecules. Here the authors present a simple approximation where the orbitals are optimized with the mean-field energy plus a correlation energy taken as the opposite-spin component of the second-order many-body correlation energy, scaled by an empirically chosen parameter (recommended as 1.2 for general applications). This "optimized second-order opposite-spin" (abbreviated as O2) method requires fourth-order computation on each orbital iteration. O2 is shown to yield predictions of structure and frequencies for closed-shell molecules that are very similar to scaled second-order Moller-Plesset methods. However, it yields substantial improvements for open-shell molecules, where problems with spin contamination and symmetry breaking are shown to be greatly reduced.

Phonon-assisted Kondo effect in a single-molecule transistor out of equilibrium

The joint effect of the electron–phonon interaction and Kondo effect on nonequilibriumtransport through a single molecule transistor is investigated by using the improvedcanonical transformation scheme and extended equation of motion approach. Two types ofKondo phonon-satellite with different asymmetric shapes are fully confirmed in the spectralfunction, and are related to the electron spin singlet or hole spin singlet, respectively.Moreover, when a moderate Zeeman splitting is caused by a local magnetic field, theKondo satellites in the spin-resolved spectral function are found to disappear on oneside of the main peak, and they disappear on the opposite side for the oppositespin component. All these peculiar signatures that manifest themselves in thenonlinear differential conductance are explained with a clear physics picture.