Electron gas at the interface between two antiferromagnetic insulating manganites

We study theoretically the magnetic and electric properties of the interface between two antiferromagnetic and insulating manganites: La0.5Ca0.5MnO3, a strong correlated insulator, and CaMnO3, a band-insulator. We find that a ferromagnetic and metallic electron gas is formed at the interface between the two layers. We confirm the metallic character of the interface by calculating the in-plane conductance. The possibility of increasing the electron gas density by selective doping is also discussed.Comment: 6 pages, including 9 figure

Transversal inhomogeneities in dilute vibrofluidized granular fluids

The spontaneous symmetry breaking taking place in the direction perpendicular to the energy flux in a dilute vibrofluidized granular system is investigated, using both a hydrodynamic description and simulation methods. The latter include molecular dynamics and direct Monte Carlo simulation of the Boltzmann equation. A marginal stability analysis of the hydrodynamic equations, carried out in the WKB approximation, is shown to be in good agreement with the simulation results. The shape of the hydrodynamic profiles beyond the bifurcation is discussed

Solitonic Phase in Manganites

Whenever a symmetry in the ground state of a system is broken, topological defects will exist. These defects are essential for understanding phase transitions in low dimensional systems[1]. Excitingly in some unique condensed matter systems the defects are also the low energy electric charge excitations. This is the case of skyrmions in quantum Hall ferromagnets[2] and solitons in polymers[3]. Orbital order present in several transitions metal compounds[4-6] could give rise to topological defects. Here we argue that the topological defects in orbital ordered half doped manganites are orbital solitons. Surprisingly, these solitons carry a fractional charge of $\pm$e/2, and whenever extra charge is added to the system an array of solitons is formed and an incommensurate solitonic phase occurs. The striking experimental asymmetry in the phase diagram as electrons or holes are added to half doped manganites[7-12], is explained by the energy difference between positive and negative charged solitons. Contrary to existent models that explain coexistence between phases in manganites as an extrinsic effect[13-14], the presence of inhomogeneities is naturally explained by the existence of solitonic phases. The occurrence and relevance of orbital solitons might be a general phenomena in strongly correlated systems.Comment: 10 pages, 5 figures include

Effect of strain on the orbital and magnetic ordering of manganite thin films and their interface with an insulator

We study the effect of uniform uniaxial strain on the ground state electronic configuration of a thin film manganite. Our model Hamiltonian includes the double-exchange, the Jahn-Teller electron-lattice coupling, and the antiferromagnetic superexchange. The strain arises due to the lattice mismatch between an insulating substrate and a manganite which produces a tetragonal distortion. This is included in the model via a modification of the hopping amplitude and the introduction of an energy splitting between the Mn e_g levels. We analyze the bulk properties of half-doped manganites and the electronic reconstruction at the interface between a ferromagnetic and metallic manganite and the insulating substrate. The strain drives an orbital selection modifying the electronic properties and the magnetic ordering of manganites and their interfaces.Comment: 8 pages, 8 figure

Zero Landau level in folded graphene nanoribbons

Graphene nanoribbons can be folded into a double layer system keeping the two layers decoupled. In the Quantum Hall regime folds behave as a new type of Hall bar edge. We show that the symmetry properties of the zero Landau level in metallic nanoribbons dictate that the zero energy edge states traversing a fold are perfectly transmitted onto the opposite layer. This result is valid irrespective of fold geometry, magnetic field strength and crystallographic orientation of the nanoribbon. Backscattering suppression on the N=0 Hall plateau is ultimately due to the orthogonality of forward and backward channels, much like in the Klein paradox.Comment: Final published version, with supplementary material appendi

Velocity distribution of fluidized granular gases in presence of gravity

The velocity distribution of a fluidized dilute granular gas in the direction perpendicular to the gravitational field is investigated by means of Molecular Dynamics simulations. The results indicate that the velocity distribution can be exactly described neither by a Gaussian nor by a stretched exponential law. Moreover, it does not exhibit any kind of scaling. In fact, the actual shape of the distribution depends on the number of monolayers at rest, on the restitution coefficient and on the height at what it is measured. The role played by the number of particle-particle collisions as compared with the number of particle-wall collisions is discussed

Instability of the symmetric Couette-flow in a granular gas: hydrodynamic field profiles and transport

We investigate the inelastic hard disk gas sheared by two parallel bumpy walls (Couette-flow). In our molecular dynamic simulations we found a sensitivity to the asymmetries of the initial condition of the particle places and velocities and an asymmetric stationary state, where the deviation from (anti)symmetric hydrodynamic fields is stronger as the normal restitution coefficient decreases. For the better understanding of this sensitivity we carried out a linear stability analysis of the former kinetic theoretical solution [Jenkins and Richman: J. Fluid. Mech. {\bf 171} (1986)] and found it to be unstable. The effect of this asymmetry on the self-diffusion coefficient is also discussed.Comment: 9 pages RevTeX, 14 postscript figures, sent to Phys. Rev.

Zener tunneling isospin Hall effect in HgTe quantum wells and graphene multilayers

A Zener diode is a paradigmatic device in semiconductor-based electronics that consists of a p-n junction where an external electric field induces a switching behavior in the current-voltage characteristics. We study Zener tunneling in HgTe quantum wells and graphene multilayers. We find that the tunneling transition probability depends asymmetrically on the parallel momentum of the carriers to the barrier. In HgTe quantum wells the asymmetry is the opposite for each spin, whereas for graphene multilayers it is the opposite for each valley degree of freedom. In both cases, a spin/valley current flowing in the perpendicular direction to the applied field is produced. We relate the origin of this Zener tunneling spin/valley Hall effect to the Berry phase acquired by the carriers when they are adiabatically reflected from the gapped regionWe acknowledge fruitful discussions with B. Dora, S. Kohler, and M. O. Goerbig. Funding for this work was provided by MICINN-Spain via Grant No. FIS2009-08744, the CSIC JAE-Doc program, and was supported in part by the National Science Foundation under Grant No. NSF PHY05-5116