Magnetic anisotropy and spin-spiral wave in V, Cr and Mn atomic chains on Cu(001) surface: First principles calculations

Recent ab intio studies of the magnetic properties of all 3d transition metal(TM) freestanding atomic chains predicted that these nanowires could have a giant magnetic anisotropy energy (MAE) and might support a spin-spiral structure, thereby suggesting that these nanowires would have technological applicationsin, e.g., high density magnetic data storages. In order to investigate how the substrates may affect the magnetic properties of the nanowires, here we systematically study the V, Cr and Mn linear atomic chains on the Cu(001) surface based on the density functional theory with the generalized gradient approximation. We find that V, Cr, and Mn linear chains on the Cu(001) surface still have a stable or metastable ferromagnetic state. However, the ferromagnetic state is unstable against formation of a noncollinear spin-spiral structure in the Mn linear chains and also the V linear chain on the atop sites on the Cu(001) surface, due to the frustrated magnetic interactions in these systems. Nonetheless, the presence of the Cu(001) substrate does destabilize the spin-spiral state already present in the freestanding V linear chain and stabilizes the ferromagnetic state in the V linear chain on the hollow sites on Cu(001). When spin-orbit coupling (SOC) is included, the spin magnetic moments remain almost unchanged, due to the weakness of SOC in 3d TM chains. Furthermore, both the orbital magnetic moments and MAEs for the V, Cr and Mn are small, in comparison with both the corresponding freestanding nanowires and also the Fe, Co and Ni linear chains on the Cu (001) surface.Comment: Accepted for publication in J. Phys. D: Applied Physic

Optimal Topological Test for Degeneracies of Real Hamiltonians

We consider adiabatic transport of eigenstates of real Hamiltonians around loops in parameter space. It is demonstrated that loops that map to nontrivial loops in the space of eigenbases must encircle degeneracies. Examples from Jahn-Teller theory are presented to illustrate the test. We show furthermore that the proposed test is optimal.Comment: Minor corrections, accepted in Phys. Rev. Let

How should one formulate, extract, and interpret `non-observables' for nuclei?

Nuclear observables such as binding energies and cross sections can be directly measured. Other physically useful quantities, such as spectroscopic factors, are related to measured quantities by a convolution whose decomposition is not unique. Can a framework for these nuclear structure `non-observables' be formulated systematically so that they can be extracted from experiment with known uncertainties and calculated with consistent theory? Parton distribution functions in hadrons serve as an illustrative example of how this can be done. A systematic framework is also needed to address questions of interpretation, such as whether short-range correlations are important for nuclear structure.Comment: 7 pages. Contribution to the "Focus issue on Open Problems in Nuclear Structure", Journal of Physics

Impact of the various spin and orbital ordering processes on multiferroic properties of orthovanadate DyVO3

The orthovanadate DyVO3 crystal, known to exhibit multiple structural, spin and orbital ordering transitions, is presently investigated on the basis of magnetization, heat capacity, resistivity, dielectric and polarization measurements. Our main result is experimental evidence for the existence of multiferroicity below a high TC of 108 K over a wide temperature range including different spin-orbital ordered states. The onset of ferroelectricity is found to coincide with the antiferromagnetic C-type spin ordering transition taking place at 108 K, which indicates that DyVO3 belongs to type II multiferroics exhibiting a coupling between magnetism and ferroelectricity. Some anomalies detected on the temperature dependence of electric polarization are discussed with respect to the nature of the spin-orbital ordered states of the V sublattice and the degree of spin alignment in the Dy sublattice. The orthovanadates RVO3 (R = rare earth or Y) form an important new category for searching for high-TC multiferroics.Comment: 25 pages, 7 figures, 68 references, one supplementary material, Physical Review B, Published 23 July 201

Resonant Subband Landau Level Coupling in Symmetric Quantum Well

Subband structure and depolarization shifts in an ultra-high mobility GaAs/Al_{0.24}Ga_{0.76}As quantum well are studied using magneto-infrared spectroscopy via resonant subband Landau level coupling. Resonant couplings between the 1st and up to the 4th subbands are identified by well-separated anti-level-crossing split resonance, while the hy-lying subbands were identified by the cyclotron resonance linewidth broadening in the literature. In addition, a forbidden intersubband transition (1st to 3rd) has been observed. With the precise determination of the subband structure, we find that the depolarization shift can be well described by the semiclassical slab plasma model, and the possible origins for the forbidden transition are discussed.Comment: 4 pages, 2 figure

A note on the realignment criterion

For a quantum state in a bipartite system represented as a density matrix, researchers used the realignment matrix and functions on its singular values to study the separability of the quantum state. We obtain bounds for elementary symmetric functions of singular values of realignment matrices. This answers some open problems proposed by Lupo, Aniello, and Scardicchio. As a consequence, we show that the proposed scheme by these authors for testing separability would not work if the two subsystems of the bipartite system have the same dimension.Comment: 11 pages, to appear in Journal of Physics A: Mathematical and Theoretica

Heavy Quark Mass Effects in Deep Inelastic Scattering and Global QCD Analysis

A new implementation of the general PQCD formalism of Collins, including heavy quark mass effects, is described. Important features that contribute to the accuracy and efficiency of the calculation of both neutral current (NC) and charged current (CC) processess are explicitly discussed. This new implementation is applied to the global analysis of the full HERA I data sets on NC and CC cross sections, with correlated systematic errors, in conjunction with the usual fixed-target and hadron collider data sets. By using a variety of parametrizations to explore the parton parameter space, robust new parton distribution function (PDF) sets (CTEQ6.5) are obtained. The new quark distributions are consistently higher in the region x ~ 10^{-3} than previous ones, with important implications on hadron collider phenomenology, especially at the LHC. The uncertainties of the parton distributions are reassessed and are compared to the previous ones. A new set of CTEQ6.5 eigenvector PDFs that encapsulates these uncertainties is also presented.Comment: 32 pages, 12 figures; updated, Publication Versio

Leptoproduction of heavy quarks

There are presently two approaches to calculating heavy quark production for the deeply inelastic scattering process in current literature. The conventional fixed-flavor scheme focuses on the flavor creation mechanism and includes the heavy quark only as a final state particle in the hard scattering cross section; this has been computed to next-to-leading order--\alphas^2. The more recently formulated variable-flavor scheme includes, in addition, the flavor excitation process where the initial state partons of all flavors contribute above their respective threshold, as commonly accepted for calculations of other high energy processes; this was initially carried out to leading order--\alphas^1. We first compare and contrast these existing calculations. As expected from physical grounds, the next-to-leading-order fixed-flavor scheme calculation yields good results near threshold, while the leading-order variable-flavor scheme calculation works well for asymptotic Q^2. The quality of the calculations in the intermediate region is dependent upon the x and Q^2 values chosen. An accurate self-consistent QCD calculation over the entire range can be obtained by extending the variable-flavor scheme to next-to-leading-order. Recent work to carry out this calculation is described. Preliminary numerical results of this calculation are also presented for comparison

Quantum Entanglement of Moving Bodies

We study the properties of quantum information and quantum entanglement in moving frames. We show that the entanglement between the spins and the momenta of two particles can be interchanged under a Lorentz transformation, so that a pair of particles that is entangled in spin but not momentum in one reference frame, may, in another frame, be entangled in momentum at the expense of spin-entanglement. Similarly, entanglement between momenta may be transferred to spin under a Lorentz transformation. While spin and momentum entanglement each is not Lorentz invariant, the joint entanglement of the wave function is.Comment: 4 pages, 2 figures. An error was corrected in the numerical data and hence the discussion of the data was changed. Also, references were added. Another example was added to the pape

Entanglement of zero angular momentum mixtures and black hole entropy

We calculate the entanglement of formation and the entanglement of distillation for arbitrary mixtures of the zero spin states on an arbitrary-dimensional bipartite Hilbert space. Such states are relevant to quantum black holes and to decoherence-free subspaces based communication. The two measures of entanglement are equal and scale logarithmically with the system size. We discuss its relation to the black hole entropy law. Moreover, these states are locally distinguishable but not locally orthogonal, thus violating a conjecture that the entanglement measures coincide only on locally orthogonal states. We propose a slightly weaker form of this conjecture. Finally, we generalize our entanglement analysis to any unitary group.Comment: 5 pages, revtex4 Final version. A discussion of local orthogonality and entanglement is adde