Static and dynamic properties of vortices in anisotropic magnetic disks

We investigate the effect of the magnetic anisotropy ($K_z$) on the static and dynamic properties of magnetic vortices in small disks. Our micromagnetic calculations reveal that for a range of $K_z$ there is an enlargement of the vortex core. We analyze the influence of $K_z$ on the dynamics of the vortex core magnetization reversal under the excitation of a pulsed field. The presence of $K_z$, which leads to better resolved vortex structures, allows us to discuss in more details the role played by the in-plane and perpendicular components of the gyrotropic field during the vortex-antivortex nucleation and annihilation.Comment: 4 pages, 4 figure

Griffiths phases in the strongly disordered Kondo necklace model

The effect of strong disorder on the one-dimensional Kondo necklace model is studied using a perturbative real-space renormalization group approach which becomes asymptotically exact in the low energy limit. The phase diagram of the model presents a random quantum critical point separating two phases; the {\em random singlet phase} of a quantum disordered XY chain and the random Kondo phase. We also consider an anisotropic version of the model and show that it maps on the strongly disordered transverse Ising model. The present results provide a rigorous microscopic basis for non-Fermi liquid behavior in disordered heavy fermions due to Griffiths phases.Comment: 4 pages, 4 figure

Adatoms and Anderson localization in graphene

We address the nature of the disordered state that results from the adsorption of adatoms in graphene. For adatoms that sit at the center of the honeycomb plaquette, as in the case of most transition metals, we show that the ones that form a zero-energy resonant state lead to Anderson localization in the vicinity of the Dirac point. Among those, we show that there is a symmetry class of adatoms where Anderson localization is suppressed, leading to an exotic metallic state with large and rare charge droplets, that localizes only at the Dirac point. We identify the experimental conditions for the observation of the Anderson transition for adatoms in graphene.Comment: 8 pages, 5 figures, 2 appendixes, Final versio

Quantum Hall Effect in Graphene with Interface-Induced Spin-Orbit Coupling

We consider an effective model for graphene with interface-induced spin-orbit coupling and calculate the quantum Hall effect in the low-energy limit. We perform a systematic analysis of the contribution of the different terms of the effective Hamiltonian to the quantum Hall effect (QHE). By analysing the spin-splitting of the quantum Hall states as a function of magnetic field and gate-voltage, we obtain different scaling laws that can be used to characterise the spin-orbit coupling in experiments. Furthermore, we employ a real-space quantum transport approach to calculate the quantum Hall conductivity and investigate the robustness of the QHE to disorder introduced by hydrogen impurities. For that purpose, we combine first-principles calculations and a genetic algorithm strategy to obtain a graphene-only Hamiltonian that models the impurity

Real-space calculation of the conductivity tensor for disordered topological matter

We describe an efficient numerical approach to calculate the longitudinal and transverse Kubo conductivities of large systems using Bastin's formulation. We expand the Green's functions in terms of Chebyshev polynomials and compute the conductivity tensor for any temperature and chemical potential in a single step. To illustrate the power and generality of the approach, we calculate the conductivity tensor for the quantum Hall effect in disordered graphene and analyze the effect of the disorder in a Chern insulator in Haldane's model on a honeycomb lattice.Comment: 5 pages, 3 figures and a supplementary material (3 pages

The effect of the Abrikosov vortex phase on spin and charge states in magnetic semiconductor-superconductor hybrids

We explore the possibility of using the inhomogeneous magnetic field carried by an Abrikosov vortex in a type-II superconductor to localize spin-polarized textures in a nearby magnetic semiconductor quantum well. We show how Zeeman-induced localization induced by a single vortex is indeed possible, and use these results to investigate the effect of a periodic vortex array on the transport properties of the magnetic semiconductor. In particular, we find an unconventional Integer Quantum Hall regime, and predict directly testable experimental consequences due to the presence of the periodic spin polarized structure induced by the superconducting vortex lattice in the magnetic semiconductor.Comment: 12 pages, 15 figure