Floquet spin states in graphene under ac driven spin-orbit interaction

We study the role of periodically driven time-dependent Rashba spin-orbit coupling (RSOC) on a monolayer graphene sample. After recasting the originally $4\times 4$ system of dynamical equations as two time-reversal related two-level problems, the quasi-energy spectrum and the related dynamics are investigated via various techniques and approximations. In the static case the system is a gapped at the Dirac point. The rotating wave approximation (RWA) applied to the driven system unphysically preserves this feature, while the Magnus-Floquet approach as well as a numerically exact evaluation of the Floquet equation show that this gap is dynamically closed. In addition, a sizable oscillating pattern of the out-of-plane spin polarization is found in the driven case for states which completely unpolarized in the static limit. Evaluation of the autocorrelation function shows that the original uniform interference pattern corresponding to time-independent RSOC gets distorted. The resulting structure can be qualitatively explained as a consequence of the transitions induced by the ac driving among the static eigenstates, i.e., these transitions modulate the relative phases that add up to give the quantum revivals of the autocorrelation function. Contrary to the static case, in the driven scenario, quantum revivals (suppresions) are correlated to spin up (down) phases.Comment: 10 pages, 8 figures. Typos corrected. Accepted for publication in PR

Graphene with time-dependent spin-orbit coupling: Truncated Magnus expansion approach

We analyze the role of ac-driven Rashba spin-orbit coupling in monolayer graphene including a spin-dependent mass term. Using the Magnus expansion as a semi-analytical approximation scheme a full account of the quasienergie spectrum of spin states is given. We discuss the subtleties arising in correctly applying the Magnus expansion technique in order to determine the quasienergy spectrum. Comparison to the exact numerical solution gives appropriate boundaries to the validity of the Magnus expansion solution.Comment: 8 pages, 4 figure

Zero-field magnetization reversal of two-body Stoner particles with dipolar interaction

Nanomagnetism has recently attracted explosive attention, in particular, because of the enormous potential applications in information industry, e.g. new harddisk technology, race-track memory[1], and logic devices[2]. Recent technological advances[3] allow for the fabrication of single-domain magnetic nanoparticles (Stoner particles), whose magnetization dynamics have been extensively studied, both experimentally and theoretically, involving magnetic fields[4-9] and/or by spin-polarized currents[10-20]. From an industrial point of view, important issues include lowering the critical switching field $H_c$, and achieving short reversal times. Here we predict a new technological perspective: $H_c$ can be dramatically lowered (including $H_c=0$) by appropriately engineering the dipole-dipole interaction (DDI) in a system of two synchronized Stoner particles. Here, in a modified Stoner-Wohlfarth (SW) limit, both of the above goals can be achieved. The experimental feasibility of realizing our proposal is illustrated on the example of cobalt nanoparticles.Comment: 5 pages, 4 figure

Search for a Standard Model Higgs Boson in the H → ZZ → ℓ^+ℓ^-vv Decay Channel with the ATLAS Detector

A search for a heavy standard model Higgs boson decaying via H→ZZ→ℓ^+ℓ^-νν̅ , where ℓ=e, μ, is presented. It is based on proton-proton collision data at √s=7  TeV, collected by the ATLAS experiment at the LHC in the first half of 2011 and corresponding to an integrated luminosity of 1.04  fb^(-1). The data are compared to the expected standard model backgrounds. The data and the background expectations are found to be in agreement and upper limits are placed on the Higgs boson production cross section over the entire mass window considered; in particular, the production of a standard model Higgs boson is excluded in the region 340<m_H<450  GeV at the 95% confidence level

Study of jet shapes in inclusive jet production in pp collisions at √s=7 TeV using the ATLAS detector

Jet shapes have been measured in inclusive jet production in proton-proton collisions at √s=7  TeV using 3  pb^(-1) of data recorded by the ATLAS experiment at the LHC. Jets are reconstructed using the anti-k_t algorithm with transverse momentum 30  GeV<pT<600  GeV and rapidity in the region |y|<2.8. The data are corrected for detector effects and compared to several leading-order QCD matrix elements plus parton shower Monte Carlo predictions, including different sets of parameters tuned to model fragmentation processes and underlying event contributions in the final state. The measured jets become narrower with increasing jet transverse momentum and the jet shapes present a moderate jet rapidity dependence. Within QCD, the data test a variety of perturbative and nonperturbative effects. In particular, the data show sensitivity to the details of the parton shower, fragmentation, and underlying event models in the Monte Carlo generators. For an appropriate choice of the parameters used in these models, the data are well described

A re-analysis of τ Ursae Majoris

Se realiza un nuevo análisis de las estrellas Am τ U Ma utilizando nuevas determinaciones de su temperatura efectiva y gravedad superficial y nuevas medidas de anchos equivalentes e identificaciones de líneas. Con el método de las curvas de crecimiento se calculan las abundancias de elementos. Se investiga la existencia de ciertos elementos pesados encontrados en las estrellas Ap más frías, especialmente aquellos con Z entre 41 y 55 pero no existe evidencia de ellos. Lo mismo sucede con los elementos más pesados de la tabla periódica.Asociación Argentina de Astronomí

A re-analysis of τ U Ma

A re-analysis of the Am star τ U Ma is carried out using new determinations of effective temperature and gravity. The abundances agree in general except a constant factor with those found by Greenstein. The existence of certain heavy elements found in the most cold Ap stars is investigated.Asociación Argentina de Astronomí

A re-analysis of τ U Ma

A re-analysis of the Am star τ U Ma is carried out using new determinations of effective temperature and gravity. The abundances agree in general except a constant factor with those found by Greenstein. The existence of certain heavy elements found in the most cold Ap stars is investigated.Asociación Argentina de Astronomí

A re-analysis of τ U Ma

A re-analysis of the Am star τ U Ma is carried out using new determinations of effective temperature and gravity. The abundances agree in general except a constant factor with those found by Greenstein. The existence of certain heavy elements found in the most cold Ap stars is investigated.Asociación Argentina de Astronomí