3,108 research outputs found
Tailoring Graphene with Metals on Top
We study the effects of metallic doping on the electronic properties of
graphene using density functional theory in the local density approximation in
the presence of a local charging energy (LDA+U). The electronic properties are
sensitive to whether graphene is doped with alkali or transition metals. We
estimate the the charge transfer from a single layer of Potassium on top of
graphene in terms of the local charging energy of the graphene sheet. The
coating of graphene with a non-magnetic layer of Palladium, on the other hand,
can lead to a magnetic instability in coated graphene due to the hybridization
between the transition-metal and the carbon orbitals.Comment: 5 pages, 4 figure
An alternative approach for the dynamics of polarons in one dimension
We developed a new method based on functional integration to treat the
dynamics of polarons in one-dimensional systems. We treat the acoustical and
the optical case in an unified manner, showing their differences and
similarities. The mobility and diffusion coefficients are calculated in the
Markovian approximation in the strong coupling limit.Comment: 57 page
Evidence for Lattice Effects at the Charge-Ordering Transition in (TMTTF)X
High-resolution thermal expansion measurements have been performed for
exploring the mysterious "structureless transition" in (TMTTF)X (X =
PF and AsF), where charge ordering at coincides with the
onset of ferroelectric order. Particularly distinct lattice effects are found
at in the uniaxial expansivity along the interstack
-direction. We propose a scheme involving a charge
modulation along the TMTTF stacks and its coupling to displacements of the
counteranions X. These anion shifts, which lift the inversion symmetry
enabling ferroelectric order to develop, determine the 3D charge pattern
without ambiguity. Evidence is found for another anomaly for both materials at
0.6 indicative of a phase transition
related to the charge ordering
Exotic Superconducting Phases of Ultracold Atom Mixtures on Triangular Lattices
We study the phase diagram of two-dimensional Bose-Fermi mixtures of
ultracold atoms on a triangular optical lattice, in the limit when the velocity
of bosonic condensate fluctuations is much larger than the Fermi velocity.
We contrast this work with our previous results for a square lattice system
in Phys. Rev. Lett. {\bf 97}, 030601 (2006).
Using functional renormalization group techniques we show that the phase
diagrams for a triangular lattice contain exotic superconducting phases. For
spin-1/2 fermions on an isotropic lattice we find a competition of -, -,
extended -, and -wave symmetry, as well as antiferromagnetic order. For
an anisotropic lattice, we further find an extended p-wave phase. A Bose-Fermi
mixture with spinless fermions on an isotropic lattice shows a competition
between - and -wave symmetry.
These phases can be traced back to the geometric shapes of the Fermi surfaces
in various regimes, as well as the intrinsic frustration of a triangular
lattice.Comment: 6 pages, 4 figures, extended version, slight modification
Negative Hopping Magnetoresistance and Dimensional Crossover in Lightly Doped Cuprate Superconductors
We show that, due to the weak ferromagnetism of LaSrCuO, an
external magnetic field leads to a dimensional crossover 2D 3D for the
in-plane transport. The crossover results in an increase of the hole's
localization length and hence in a dramatic negative magnetoresistance in the
variable range hopping regime. This mechanism quantitatively explains puzzling
experimental data on the negative magnetoresistance in the N\'eel phase of
LaSrCuO.Comment: 6 pages, 3 figures; published versio
- …