301 research outputs found
Partial preservation of chiral symmetry and colossal magnetoresistance in adatom doped graphene
We analyze the electronic properties of adatom doped graphene in the low
impurity concentration regime. We focus on the Anderson localized regime and
calculate the localization length () as a function of the electron doping
and an external magnetic field. The impurity states hybridize with carbon's
states and form a partially filled band close to the Dirac point. Near
the impurity band center, the chiral symmetry of the system's effective
Hamiltonian is partially preserved which leads to a large enhancement of .
The sensitivity of transport properties, namely Mott's variable range hopping
scale , to an external magnetic field perpendicular to the graphene sheet
leads to a colossal magnetoresistance effect, as observed in recent
experiments.Comment: 5 pages, 4 figs. Few comments and references added. To appear in PR
Localized Spins on Graphene
The problem of a magnetic impurity, atomic or molecular, absorbed on top of a
carbon atom in otherwise clean graphene is studied using the numerical
renormalization group. The spectral, thermodynamic, and scattering properties
of the impurity are described in detail. In the presence of a small magnetic
field, the low energy electronic features of graphene make possible to inject
spin polarized currents through the impurity using a scanning tunneling
microscope (STM). Furthermore, the impurity scattering becomes strongly spin
dependent and for a finite impurity concentration it leads to spin polarized
bulk currents and a large magnetoresistance. In gated graphene the impurity
spin is Kondo screened at low temperatures. However, at temperatures larger
than the Kondo temperature, the anomalous magnetotransport properties are
recovered.Comment: 4+ pages, 4 figures. Added reference
Transport properties and structures of vortex matter in layered superconductors
In this paper we analyze the structure, phase transitions and some transport
properties of the vortex system when the external magnetic field lies parallel
to the planes in layered superconductors. We show that experimental results for
resistivity are qualitatively consistent with numerical simulations that
describe the melting of a commensurate rotated lattice. However for some
magnetic fields, the structure factor indicates the occurrence of smectic peaks
at an intermediate temperature regime.Comment: 8 pages, 8 eps figure
Transport through quantum dots in mesoscopic circuits
We study the transport through a quantum dot, in the Kondo Coulomb blockade
valley, embedded in a mesoscopic device with finite wires. The quantization of
states in the circuit that hosts the quantum dot gives rise to finite size
effects. These effects make the conductance sensitive to the ratio of the Kondo
screening length to the wires length and provide a way of measuring the Kondo
cloud. We present results obtained with the numerical renormalization group for
a wide range of physically accessible parameters.Comment: 4 pages, 5 figure
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