6,362 research outputs found
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
Impurities and electronic localization in graphene bilayers
We analyze the electronic properties of bilayer graphene with Bernal stacking
and a low concentration of adatoms. Assuming that the host bilayer lies on top
of a substrate, we consider the case where impurities are adsorbed only on the
upper layer. We describe non-magnetic impurities as a single orbital hybridized
with carbon's pz states. The effect of impurity doping on the local density of
states with and without a gated electric field perpendicular to the layers is
analyzed. We look for Anderson localization in the different regimes and
estimate the localization length. In the biased system, the field induced gap
is partially filled by strongly localized impurity states. Interestingly, the
structure, distribution and localization length of these states depend on the
field polarization.Comment: 7 pages, 6 figure
Perception and Barriers to Indoor Air Quality and Perceived Impact on Respiratory Health: An Assessment in Rural Honduras
Objective. The aim of this study was to identify household-specific factors associated with respiratory symptoms and to study the perceived impact of indoor air pollution (IAP) as a health issue. Methods. An IRB-approved, voluntary, anonymous 23-item survey was conducted in Spanish at a medical outreach clinic in June 2012 and at the homes of survey respondents (N = 79). Comparative analyses were performed to investigate relationships between specific house characteristics and respiratory complaints. Results. Seventy-nine surveys were completed. Respiratory symptoms were frequently reported by survey respondents: 42% stated that smoke in their household caused them to have watery eyes, 42% reported household members with coughs within the past two weeks, and 25% stated that there were currently household members experiencing difficulty in breathing. Stove location and kitchen roof construction material were significantly associated with frequency of respiratory symptoms. The vast majority used firewood as their major fuel type. Most respondents indicated that neither indoor air quality was a problem nor did it affect their daily life. Conclusions. Respiratory complaints are common in Yoro, Honduras. Stove location and kitchen roof construction material were significantly associated with frequency of respiratory symptoms; this may have implications for efforts to improve respiratory health in the region
Competing Ferromagnetic and Charge-Ordered States in Models for Manganites: the Origin of the CMR Effect
The one-orbital model for manganites with cooperative phonons and
superexchange coupling has been investigated via large-scale Monte
Carlo (MC) simulations. Results for two-orbitals are also briefly discussed.
Focusing on electronic density =0.75, a regime of competition between
ferromagnetic (FM) metallic and charge-ordered (CO) insulating states was
identified. In the vicinity of the associated bicritical point, colossal
magnetoresistance (CMR) effects were observed. The CMR is associated with the
development of short-distance correlations among polarons, above the spin
ordering temperatures, resembling the charge arrangement of the low-temperature
CO state.Comment: 4 pages, 4 figures, accepted for publication in the Phys. Rev. Let
Electronic Transport through Magnetic Molecules with Soft Vibrating Modes
The low-temperature transport properties of a molecule are studied in the
field-effect transitor geometry. The molecule has an internal mechanical mode
that modulates its electronic levels and renormalizes both the interactions and
the coupling to the electrodes. For a soft mechanical mode the spin
fluctuations in the molecule are dominated by the bare couplings while the
valence changes are determined by the dressed energies. In this case, the
transport properties present an anomalous behavior and the Kondo temperature
has a weak gate voltage dependence. These observations are in agreement with
recent experimental data.Comment: 4 pages, 3 figures, accepted in PRB R
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