110 research outputs found
Oxygen adsorption effect on magnetic properties of graphite
Both experimental and theoretical studies of the magnetic properties of
micrographite and nanographite indicate a crucial role of the partial oxidation
of graphitic zigzag edges in ferromagnetism. In contrast to total and partial
hydrogenation, the oxidation of half of the carbon atoms on the graphite edges
transforms the antiferromagnetic exchange interaction between graphite planes
and over graphite ribbons to the ferromagnetic interaction. The stability of
the ferromagnetism is discussed.Comment: 14 pages, 6 figure
Disorder and interaction effects in two dimensional graphene sheets
The interplay between different types of disorder and electron-electron
interactions in graphene planes is studied by means of Renormalization Group
techniques. The low temperature properties of the system are determined by
fixed points where the strength of the interactions remains finite, as in one
dimensional Luttinger liquids. These fixed points can be either stable
(attractive), when the disorder is associated to topological defects in the
lattice or to a random mass term, or unstable (repulsive) when the disorder is
induced by impurities outside the graphene planes. In addition, we analyze
mid-gap states which can arise near interfaces or vacancies.Comment: 4 pages, 3 figure
Local superconductivity and ferromagnetism interplay in graphite-sulfur composites
The superconductivity of graphite-sulfur composites is highly anisotropic and associated with the graphite planes. The superconducting state coexists with the ferromagnetism of pure graphite, and a continuous crossover from superconducting to ferromagnetic-like behavior could be achieved by increasing the magnetic field or the temperature. The angular dependence of the magnetic moment m(alpha) provides evidence for an interaction between the ferromagnetic and the superconducting order parameters.76276
Vortex Lattice in Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta} Well Above the First-Order Phase-Transition Boundary
Measurements of non-local in-plane resistance originating from transverse
vortex-vortex correlations have been performed on a
Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta} high-T_c superconductor in a magnetic field up
to 9 T applied along the crystal c-axis. Our results demonstrate that a rigid
vortex lattice does exist over a broad portion of the magnetic field --
temperature (H-T) phase diagram, well above the first-order transition boundary
H_{FOT}(T). The results also provide evidence for the vortex lattice melting
and vortex liquid decoupling phase transitions, occurring above the H_{FOT}(T).Comment: 14 pages, 10 figure
Universal Magnetic-Field-Driven Metal-Insulator-Metal Transformations in Graphite and Bismuth
Applied magnetic field induces metal - insulator and re-entrant
insulator-metal transitions in both graphite and rhombohedral bismuth. The
corresponding transition boundaries plotted on the magnetic field - temperature
(B - T) plane nearly coincide for these semimetals and can be best described by
power laws T ~ (B - B_c)^k, where B_c is a critical field at T = 0 and k = 0.45
+/- 0.05. We show that insulator-metal-insulator (I-M-I) transformations take
place in the Landau level quantization regime and illustrate how the IMT in
quasi-3D graphite transforms into a cascade of I-M-I transitions, related to
the quantum Hall effect in quasi-2D graphite samples. We discuss the possible
coupling of superconducting and excitonic correlations with the observed
phenomena, as well as the signatures of quantum phase transitions associated
with the M-I and I-M transformations.Comment: 23 pages including 14 figure
Interaction Between Superconducting and Ferromagnetic Order Parameters in Graphite-Sulfur Composites
The superconductivity of graphite-sulfur composites is highly anisotropic and
associated with the graphite planes. The superconducting state coexists with
the ferromagnetism of pure graphite, and a continuous crossover from
superconducting to ferromagnetic-like behavior could be achieved by increasing
the magnetic field or the temperature. The angular dependence of the magnetic
moment m(alpha) provides evidence for an interaction between the ferromagnetic
and the superconducting order parameters.Comment: 11 pages, 4 figures, to be published in Phys. Rev.
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