Polarization effect on the spin symmetry for anti-Lambda spectrum in ^16O＋∧ system

^The polarization effect on the spin symmetry for anti-Lambda spectrum in 16 O＋Λ system has been studied in relativistic mean-field theory.The PK1 effective interaction is used for nucleon-meson couplings and G-parity symmetry with a reduction factor ξ = 0.3 is adopted for anti-Lambda-meson couplings.The energy differences between spin doublets in the anti-Lambda spectrum are around 0.10-0.73 MeV for p Λ state.The dominant components of the Dirac spinor for the anti-Lambda spin doublets are found to be near identical.It indicates that the spin symmetry is still well-conserved against the polarization effect from the valence antiLambda hyperon,which leads to a highly compressed cold nucleus with the central density up to 2 - 3 times of saturated density.     

Spin Symmetry for Anti-Lambda Spectrum in Atomic Nucleus

The spin symmetry of the anti-Lambda spectrum in nucleus 16O is studied in the relativistic mean field theory. The spin-orbit splittings of spin doublets are found to be around 0.03-0.07MeV and the dominant components of the Dirac spinor for the anti-Lambda spin doublets are found to be near identical. It is indicated that there is an even better spin symmetry in the anti-Lambda spectrum than that in the anti-nucleon spectrum.     

Spin and Charge Currents through a Quantum Dot Connected to Ferromagnetic Leads

We investigate the spin polarized current through a quantum dot connected to ferromagnetic leads in the presence of a finite spin-dependent chemical potential. The effects of the spin polarization of the leads p and the external magnetic field B are studied. It is found that both the magnitude and the symmetry of the current are dependent on the spin polarization of the leads. When the two ferromagnetic leads are in parallel configuration, the spin polarization p has an insignificant effect on the spin current, and an accompanying charge current appears with the increase of p. When the leads are in antiparallel configuration, however, the effect of p is distinct. The charge current is always zero regardless of the variation of p in the absence of B. The peaks appearing in the pure spin current are greatly suppressed and become asymmetric as p is increased. The applied magnetic field B results in an accompanying charge current in both the parallel and antiparallel configurations of the leads. The characteristics of the currents are explained in terms of the density of states of the quantum dot.     

Tunable valley filter efficiency by spin–orbit coupling in silicene nanoconstrictions

Valley filter is a promising device for producing valley polarized current in graphene-like two-dimensional honeycomb lattice materials. The relatively large spin–orbit coupling in silicene contributes to remarkable quantum spin Hall effect, which leads to distinctive valley-dependent transport properties compared with intrinsic graphene. In this paper,quantized conductance and valley polarization in silicene nanoconstrictions are theoretically investigated in quantum spinHall insulator phase. Nearly perfect valley filter effect is found by aligning the gate voltage in the central constriction region. However, the valley polarization plateaus are shifted with the increase of spin–orbit coupling strength, accompanied by smooth variation of polarization reversal. Our findings provide new strategies to control the valley polarization in valleytronic devices.     

Spin polarization effect for Mn2 molecule

The density functional theory method （DFT） （b3p86） of Gaussian 03 has been used to optimize the structure of the Mn2 molecule. The result shows that the ground state of the Mn2 molecule is an 11-multiple state, indicating a spin polarization effect in the Mn2 molecule, a transition metal element molecule. Meanwhile, we have not found any spin pollution because the wavefunction of the ground state does not mingle with wavefunctions of higher-energy states. So the ground state for Mn2 molecule being of an 11-multiple state is the indicative of spin polarization effect of the Mn2 molecule among those in the transition metal elements： that is, there are 10 parallel spin electrons in a Mn2 molecule. The number of non-conjugated electrons is the greatest. These electrons occupy different spacious orbitals so that the energy of the Mn2 molecule is minimized. It can be concluded that the effect of parallel spin in the Mn2 molecule is larger than the effect of the conjugated molecule, which is obviously related to the effect of electron d delocalization. In addition, the Murrell-Sorbie potential functions with the parameters for the ground state and other states of the Mn2 molecule are derived. The dissociation energy De for the ground state of the Mn2 molecule is 1.4477 eV, equilibrium bond length Re is 0.2506 nm, vibration frequency ωe is 211.51 cm^-1. Its force constants f2, f3, and f4 are 0.7240 aJ·nm-2, -3.35574 aJ·nm^-3, 11.4813 aJ·nm^-4 respectively. The other spectroscopic data for the ground state of the Mn2 molecule ωeχe, Be, αe are 1.5301 cm^-1, 0.0978 cm^-1, 7.7825×10^-4 cm^-1 respectively.     

Spin polarization effect of Ni2 molecule

The density functional theory （DFT） method （b3p86） of Gaussian 03 is used to optimize the structure of the Ni2 molecule. The result shows that the ground state for the Ni2 molecule is a 5-multiple state, symbolizing a spin polarization effect existing in the Ni2 molecule, a transition metal molecule, but no spin pollution is found because the wavefunction of the ground state does not mingle with wavefunctions of higher-energy states. So the ground state for Ni2 molecule, which is a 5-multiple state, is indicative of spin polarization effect of the Ni2 molecule, that is, there exist 4 parallel spin electrons in Ni2 molecule. The number of non-conjugated electrons is greatest. These electrons occupy different spatial orbitals so that the energy of the Ni2 molecule is minimized. It can be concluded that the effect of parallel spin in the Ni2 molecule is larger than that of the conjugated molecule, which is obviously related to the effect of electron d delocalization. In addition, the Murrell-Sorbie potential functions with the parameters of the ground state and other states of the Ni2 molecule are derived. The dissociation energy De for the ground state of the Ni2 molecule is 1.835 eV, equilibrium bond length Re is 0.2243 nm, vibration frequency we is 262.35 cm^-1. Its force constants f2, f3 and f4 are 1.1901 aJ.nm^-2, -5.8723 aJ.nm^-3, and 21.2505 aJ.nm^-4 respectively. The other spectroscopic data for the ground state of the Ni2 molecule ωeχe, Be and αe are 1.6315cm 2, 0.1141 cm^-1, and 8.0145× 10^-4 cm^-1 respectively.     

Thermodynamic Stability,Half-Metallic and Optical Properties of Sc2CoSi [001] Film:a DFT Study

The electronic and optical characteristics of the Sc2 CoSi Heusler with L21 structure and also the surface effect on electronic and optical properties, and the ?lms thermodynamic stability of the [001] direction in four cases including:Sc-Sc, Sc-Co, Sc-Si and Co-Si terminations are studied using the ?rst principles calculations(FPLAPW) within the framework of the density functional theory(DFT). The band structure calculations represent the ferromagnetic halfmetallic properties with 100% spin polarization and 0.54 e V indirect gap in spin down for Sc2 CoSi bulk with optimized lattice parameters of 6.25 A?. The total magnetic moment obtained for this compound is-1.0 μB, which is in accordance with Slater-Pauling rule. The half-metallic(HM) behavior by 100% spin polarization at Fermi level is occurred in the Sc-Si termination with a 0.32 eV gap in down spin. The optical responses have been calculated for the bulk and ScSi termination by a red shift in these parameters and the metallic treatments have been increased. According to the thermodynamic phase diagrams, it is shown the Sc-Si and Sc-Sc terminations are more stable than other terminations.     

Spin-Polarized States of Nuclear Matter

The equations of state of spin-polarized nuclear matter and pure neutron matter are studied in theframework of the Brueckner-Hartree-Fock theory including a three-body force. The energy per nucleon E A (δ) calculatedin the full range of spin polarization δ = (ρ↑ - ρ↓)/ρ for symmetric nuclear matter and pure neutron matter fulfills aparabolic law. In both the cases the spin-symmetry energy is calculated as a function of the baryonic density alongwith the related quantities such as the magnetic susceptibility and the Landau parameter Go. The main effect of thethree-body force is to strongly reduce the degenerate Fermi gas magnetic susceptibility even more than the value withonly two-body force. The equation of state is monotonically increasing with the density for all spin-aligned configurationsstudied here so that no any signature is found for a spontaneous transition to a ferromagnetic state.     

Spin polarization effect for Cr2 molecule

Density functional theory （DFT） （B3P86） of Gaussian 03 has been used to optimize the structure of the Cr2 molecule, a transition metal element molecule. The result shows that the ground state for the Cr2 molecule is a 13- multiple state, indicating that there exists a spin polarization effect in the Cr2 molecule. Meanwhile, we have not found any spin pollution because the wave function of the ground state does not mingle with wave functions of higher-energy states. So the ground state for Cr2 molecule being a 13-multiple state is indicative of spin polarization effect of the Cr2 molecule among transition metal elements, that is, there are 12 parallel spin electrons in the Cr2 molecule. The number of non-conjugated electrons is greatest. These electrons occupy different spatial orbitals so that the energy of the Cr2 molecule is minimized. It can be concluded that the effect of parallel spin in the Cr2 molecule is larger than the effect of the conjugated molecule, which is obviously related to the effect of electron d delocalization. In addition, the Murrell Sorbie potential functions with the parameters for the ground state and other states of the Cr2 molecule are derived. The dissociation energy De for the ground state of the Cr2 molecule is 0.1034eV, equilibrium bond length Re is 0.3396 nm, and vibration frequency we is 73.81cm^-1. Its force constants f2, f3 and f4 are 0.0835, -0.2831 and 0.3535 aJ. nm^-4 respectively. The other spectroscopic data for the ground state of the Cr2 molecule ωeχe, Be and αe are 1.2105, 0.0562 and 7.2938 x 10^-4cm^-1 respectively.     

Spin polarization effect for Fe2 molecule

This paper uses the density functional theory （DFT）（B3p86） of Gaussian03 to optimize the structure of Fe2 molecule. The result shows that the ground state for Fe2 molecule is a 9-multiple state, which shows spin polarization effect of Fe2 molecule of transition metal elements for the first time. Meanwhile, we have not found any spin pollution because the wavefunction of the ground state does not mingle with wavefunctions with higher energy states. So, that the ground state for Fe2 molecule is a 9-multiple state is indicative of the spin polarization effect of Fe2 molecule of transition metal elements. That is, there exist 8 parallel spin electrons. The non-conjugated electron is greatest in number. These electrons occupy different spacious tracks, so that the energy of the Fe2 molecule is minimized. It can be concluded that the effect of parallel spin of the Fe2 molecule is laFger than the effect of the conjugated molecule, which is obviously related to the effect of electron d delocalization. In addition, the Murrell Sorbie potential functions with the parameters for the ground state and other states of Fe2 molecule are derived. Dissociation energy De for the ground state of Fe2 molecule is 2.8586ev, equilibrium bond length Re is 0.2124nm, vibration frequency we is 336.38 cm^-1. Its force constants f2, f3, and f4 are 1.8615aJ.nm^-2, -8.6704aJ.nm^-3, 29.1676aj.nm^-4 respectively. The other spectroscopic data for the ground state of Fe2 molecule weXe, Be, αe are 1.5461 cm^-1, 0.1339cm^-1, 7.3428× 10^-4 cm^-1 respectively.     

Generalized Rashba Coupling Approximation to a Resonant Spin Hall Effect of the Spin–Orbit Coupling System in a Magnetic Field

We introduce a generalized Rashba coupling approximation to analytically solve confined two-dimensional electron systems with both the Rashba and Dresselhaus spin–orbit couplings in an external magnetic field. A solvable Hamiltonian is obtained by performing a simple change of basis, which has the same form as that with only Rashba coupling. Each Landau state becomes a new displaced-Fock state instead of the original Harmonic oscillator Fock state. Analytical energies are consistent with the numerical ones in a wide range of coupling strength even for a strong Zeeman splitting, exhibiting the validity of the analytical approximation. By using the eigenstates, spin polarization correctly displays a jump at the energy-level crossing point, where the corresponding spin conductance exhibits a pronounced resonant peak. As the component of the Dresselhaus coupling increases,the resonant point shifts to a smaller value of the magnetic field. In contrast to pure Rashba couplings, we find that the Dresselhaus coupling and Zeeman splittings tend to suppress the resonant spin Hall effect. Our method provides an easy-to-implement analytical treatment to two-dimensional electron gas systems with both types of spin–orbit couplings by applying a magnetic field.     

Maximal symmetry and mass generation of Dirac fermions and gravitational gauge field theory in six-dimensional spacetime

The relativistic Dirac equation in four-dimensional spacetime reveals a coherent relation between the dimensions of spacetime and the degrees of freedom of fermionic spinors. A massless Dirac fermion generates new symmetries corresponding to chirality spin and charge spin as well as conformal scaling transformations. With the introduction of intrinsic W-parity, a massless Dirac fermion can be treated as a Majorana-type or Weyl-type spinor in a six-dimensional spacetime that reflects the intrinsic quantum numbers of chirality spin. A generalized Dirac equation is obtained in the six-dimensional spacetime with a maximal symmetry. Based on the framework of gravitational quantum field theory proposed in Ref. [1] with the postulate of gauge invariance and coordinate independence, we arrive at a maximally symmetric gravitational gauge field theory for the massless Dirac fermion in six-dimensional spacetime. Such a theory is governed by the local spin gauge symmetry SP(1,5) and the global Poincar′e symmetry P(1,5)= SO(1,5) P~(1,5) as well as the charge spin gauge symmetry SU(2). The theory leads to the prediction of doubly electrically charged bosons. A scalar field and conformal scaling gauge field are introduced to maintain both global and local conformal scaling symmetries. A generalized gravitational Dirac equation for the massless Dirac fermion is derived in the six-dimensional spacetime. The equations of motion for gauge fields are obtained with conserved currents in the presence of gravitational effects. The dynamics of the gauge-type gravifield as a Goldstone-like boson is shown to be governed by a conserved energy-momentum tensor, and its symmetric part provides a generalized Einstein equation of gravity. An alternative geometrical symmetry breaking mechanism for the mass generation of Dirac fermions is demonstrated.     

Topological superfluid in a two-dimensional polarized Fermi gas with spin-orbit coupling and adiabatic rotation

We study the properties of superfluid in a two-dimensional(2 D) polarized Fermi gas with spin–orbit coupling and adiabatic rotation which are trapped in a harmonic potential. Due to the competition between polarization, spin–orbit coupling, and adiabatic rotation, the Fermi gas exhibits many intriguing phenomena. By using the Bardeen–Cooper–Schrieffer(BCS) mean-field method with local density approximation, we investigate the dependence of order parameter solution on the spin–orbit coupling strength and the rotation velocity. The energy spectra with different rotation velocities are studied in detail. Besides, the conditions for the zero-energy Majorana fermions in topological superfluid phase to be observed are obtained. By investigating distributions of number density, we find that the rotation has opposite effect on the distribution of number density with different spins, which leads to the enhancement of the polarization of Fermi gas. Here,we focus on the region of BCS pairing and ignore the Fulde–Ferrell–Larkin–Ovchinnikov state.     

Fano Resonance by Symmetry Breaking Stub in a Metal-Dielectric-Metal Waveguide

The coupling of a stub obliquely intersected with a metal-dielectric-metal plasmonic waveguide is investigated by using the finite difference in time domain method. Results show that an odd mode, except for the usual even mode, is excited in the stub due to the symmetry breaking of the oblique intersection. Moreover, the results show that tile quality factor of the odd mode is very high in comparison with that of the usual even mode, which is then explained by the symmetry breaking of the oblique stub intersection. The superposition of the even and the odd mode generates a Fano shaped spectrum with a very narrow linewidth. The effect of metallic loss and compensation are also discussed. Both the stub and the waveguide are compact in size, and simple in structure, which are beneficial for the achievements of narrow band filtering, sensing, lasing, and nonlinearity enhancement.     

Spin Transport in a Magnetic Superlattice with Broken Two-Fold Symmetry

We theoretically investigate the spin-dependent electron transport properties in a magnetic superlattice （MSL） with broken two-fold symmetry. An abnormal barrier in the MSL can break the two-fold symmetry of the system when it is not located at the two-fold symmetry center. A two-fold symmetry breaking factor is introduced to describe the two-fold symmetry breaking degree. Our numerical calculations show that the transmission, the conductance and the spin polarization are non-trivially dependent on the two-fold symmetry breaking factor. When the factor is large enough, the polarization almost approaches 100% in a proper Fermi energy range. However, for two mutually mirror-symmetric MSLs with the same factor, their polarizations may be either similar or distinct. These features provide some clues to the design and applications of MSL-based spin filters or spin-dependent tunneling electron devices.     

Assignment of Photoelectron Spectra of MC2 （M= V, Cr, Fe, and Co）

Hybrid density functional theory （DFT） calculations are performed to study MC2 （M= V, Cr, Fe and Co） clusters in the neutral and anionic charge states. We find that the equilibrium geometries of MC2 and their anions are all cyclic structures with C2v symmetry, which agrees well with the previous theoretical studies. The Mulliken charge and spin populations of MC2 clusters and their anions are also calculated, and it is found that the electron charge transformations from anions to neutral molecules mainly take place on the M atoms. Time-dependent DFT is used to calculate the excited states, and a theoretical assignment for the features in the experimental photoelectron spectrum is given, which are in good agreement with the available experimental data.     

The spin and pseudospin symmetries in the relativistic formalism: Similarities and differences

The effects of the symmetry breaking terms, spin-orbit potential (SOP) and pseudospin-orbit potential (PSOP), in the spin and pseudospin symmetries, respectively, are studied in a comparative way. The analytical properties of the small component F of the Dirac spinor for pseudospin doublets (PSDs) are investigated around the singularity point of the PSOP. We show that the PSOP and the pseudocentrifugal barrier must be appropriately related to each other to describe adequately the wave functions in the nuclear surface, whereas it is not the case for the centrifugal barrier and the SOP. We also determine a modified PSOP smaller than the PSOP when the parameter ˉ, appearing in it, is left to vary in the domain of real numbers. The inclusion of this modified PSOP allows us to define a continuous way that connects the two states of a PSD as ˉ varies continuously between the physical (integer) values of ˉ corresponding to these states. Our results indicate that whereas the SOP can be considered as a small spin symmetry breaking term that allows a simple explanation of the spin symmetry, the consideration of the PSOP as the pseudospin symmetry breaking term presents serious difficulties. Thus, we propose a new strategy to explain, in a simple way, the quasi-degeneracy of the PSDs.     

Exact solution of Dirac equation for Scarf potential with new tensor coupling potential for spin and pseudospin symmetries using Romanovski polynomials

The bound state solutions of Dirac equations for a trigonometric Scarf potential with a new tensor potential under spin and pseudospin symmetry limits are investigated using Romanovski polynomials. The proposed new tensor potential is inspired by superpotential form in supersymmetric(SUSY) quantum mechanics. The Dirac equations with trigonometric Scarf potential coupled by a new tensor potential for the pseudospin and spin symmetries reduce to Schrdinger-type equations with a shape invariant potential since the proposed new tensor potential is similar to the superpotential of trigonometric Scarf potential. The relativistic wave functions are exactly obtained in terms of Romanovski polynomials and the relativistic energy equations are also exactly obtained in the approximation scheme of centrifugal term. The new tensor potential removes the degeneracies both for pseudospin and spin symmetries.     

Spin transport properties for B-doped zigzag silicene nanoribbons with different edge hydrogenations

Exploring silicon-based spin modulating junction is one of the most promising areas of spintronics.Using nonequilibrium Green's function combined with density functional theory,a set of spin filters of hydrogenated zigzag silicene nanoribbons is designed by substituting a silicon atom with a boron one and the spin-correlated transport properties are studied.The results show that the spin polarization can be realized by structural symmetry breaking induced by boron doping.Remarkably,by tuning the edge hydrogenation,it is found that the spin filter efficiency can be varied from 30%to 58%.Moreover,it is also found and explained that the asymmetric hydrogenation can give rise to an obvious negative differential resistance which usually appears at weakly coupled junction.These findings indicate that the boron-doped ZSiNR is a promising material for spintronic applications.     

Spin Injection from Ferromagnetic Metal Directly into Non-Magnetic Semiconductor under Different Injection Currents

For ferromagnetic metal （FM）/semiconductor （SO） structure with ohmic contact, the effect of carrier polarization in the semiconductor combined with drift part of injection current on current polarization is investigated. Based on the general model we established here, spin injection efficiency under different injection current levels is calculated. Under a reasonable high injection current, current polarization in the semiconductor is actually much larger than that predicted by the conductivity mismatch model because the effect of carrier polarization is enhanced by the increasing drift current. An appreciable current polarization of 1% could be achieved for the FM/SC structure via ohmic contact, which means that efficient spin injection from FM into SC via ohmic contact is possible. The reported dependence of current polarization on temperature is verified quantitatively. To achieve even larger spin injection efficiency, a gradient doping semiconductor is suggested to enhance the drift current effect.