Effect of hybridization on the magnetic properties of correlated two-band metals

The magnetic properties of transition-like metals are discussed within the single site approximation, which is a picture to take into account electron correlations. The metal is described by two hybridized bands one of which includes Coulomb correlation. The presented results indicate that ferromagnetism arises for adequate values of hybridization (V), correlation (U) and occupation number($n_{\sigma}$). Some similarities with Dynamical Mean-Field Theory (DMFT) are indicated.Comment: 3 pages, 3 figures, presented at the 53rd MMM08 conference in Austin, 200

Scaling laws for the decay of multiqubit entanglement

We investigate the decay of entanglement of generalized N-particle Greenberger-Horne-Zeilinger (GHZ) states interacting with independent reservoirs. Scaling laws for the decay of entanglement and for its finite-time extinction (sudden death) are derived for different types of reservoirs. The latter is found to increase with the number of particles. However, entanglement becomes arbitrarily small, and therefore useless as a resource, much before it completely disappears, around a time which is inversely proportional to the number of particles. We also show that the decay of multi-particle GHZ states can generate bound entangled states.Comment: Minor mistakes correcte

Wavepacket scattering on graphene edges in the presence of a (pseudo) magnetic field

The scattering of a Gaussian wavepacket in armchair and zigzag graphene edges is theoretically investigated by numerically solving the time dependent Schr\"odinger equation for the tight-binding model Hamiltonian. Our theory allows to investigate scattering in reciprocal space, and depending on the type of graphene edge we observe scattering within the same valley, or between different valleys. In the presence of an external magnetic field, the well know skipping orbits are observed. However, our results demonstrate that in the case of a pseudo-magnetic field, induced by non-uniform strain, the scattering by an armchair edge results in a non-propagating edge state.Comment: 8 pages, 7 figure

Thermal Stability of the Magnetization in Perpendicularly Magnetized Thin Film Nanomagnets

Understanding the stability of thin film nanomagnets with perpendicular magnetic anisotropy (PMA) against thermally induced magnetization reversal is important when designing perpendicularly magnetized patterned media and magnetic random access memories. The leading-order dependence of magnetization reversal rates are governed by the energy barrier the system needs to surmount in order for reversal to proceed. In this paper we study the reversal dynamics of these systems and compute the relevant barriers using the string method of E, Vanden-Eijnden, and Ren. We find the reversal to be often spatially incoherent; that is, rather than the magnetization flipping as a rigid unit, reversal proceeds instead through a soliton-like domain wall sweeping through the system. We show that for square nanomagnetic elements the energy barrier increases with element size up to a critical length scale, beyond which the energy barrier is constant. For circular elements the energy barrier continues to increase indefinitely, albeit more slowly beyond a critical size. In both cases the energy barriers are smaller than those expected for coherent magnetization reversal.Comment: 5 pages, 4 Figure

All-strain based valley filter in graphene nanoribbons using snake states

A pseudo-magnetic field kink can be realized along a graphene nanoribbon using strain engineering. Electron transport along this kink is governed by snake states that are characterized by a single propagation direction. Those pseudo-magnetic fields point towards opposite directions in the K and K' valleys, leading to valley polarized snake states. In a graphene nanoribbon with armchair edges this effect results in a valley filter that is based only on strain engineering. We discuss how to maximize this valley filtering by adjusting the parameters that define the stress distribution along the graphene ribbon.Comment: 8 pages, 6 figure

Multipartite quantum nonlocality under local decoherence

We study the nonlocal properties of two-qubit maximally-entangled and N-qubit Greenberger-Horne-Zeilinger states under local decoherence. We show that the (non)resilience of entanglement under local depolarization or dephasing is not necessarily equivalent to the (non)resilience of Bell-inequality violations. Apart from entanglement and Bell-inequality violations, we consider also nonlocality as quantified by the nonlocal content of correlations, and provide several examples of anomalous behaviors, both in the bipartite and multipartite cases. In addition, we study the practical implications of these anomalies on the usefulness of noisy Greenberger-Horne-Zeilinger states as resources for nonlocality-based physical protocols given by communication complexity problems. There, we provide examples of quantum gains improving with the number of particles that coexist with exponentially-decaying entanglement and non-local contents.Comment: 6 pages, 4 figure

Micromagnetic Simulations of Ferromagnetic Rings

Thin nanomagnetic rings have generated interest for fundamental studies of magnetization reversal and also for their potential in various applications, particularly as magnetic memories. They are a rare example of a geometry in which an analytical solution for the rate of thermally induced magnetic reversal has been determined, in an approximation whose errors can be estimated and bounded. In this work, numerical simulations of soft ferromagnetic rings are used to explore aspects of the analytical solution. The evolution of the energy near the transition states confirms that, consistent with analytical predictions, thermally induced magnetization reversal can have one of two intermediate states: either constant or soliton-like saddle configurations, depending on ring size and externally applied magnetic field. The results confirm analytical predictions of a transition in thermally activated reversal behavior as magnetic field is varied at constant ring size. Simulations also show that the analytic one dimensional model continues to hold even for wide rings

Microfenótipos e proteínas associados à expressão da resistência durável à ferrugem da folha do trigo.

Editores técnicos: Joseani Mesquita Antunes, Ana Lídia Variani Bonato, Márcia Barrocas Moreira Pimentel