21,918 research outputs found
Phase Diagram of Spinless Fermions on an Anisotropic Triangular Lattice at Half-filling
The strong coupling phase diagram of the spinless fermions on the anisotropic
triangular lattice at half-filling is presented. The geometry of inter-site
Coulomb interactions rules the phase diagram. Unconventional charge ordered
phases are detected which are the recently reported pinball liquid and the
striped chains. Both are induced by the quantum dynamics out of classical
disordered states and afford extremely correlated metallic states and the
particular domain wall-type of excitations, respectively. The disorder once
killed by the quantum effect revives at the finite temperature, which is
discussed in the terms of the organic -ET.Comment: 4pages 6figure
Novel Charge Order and Superconductivity in Two-Dimensional Frustrated Lattice at Quarter Filling
Motivated by the various physical properties observed in
-(BEDT-TTF)X, we study the ground state of extended Hubbard model
on two-dimensional anisotropic triangular lattice at 1/4-filling with
variational Monte Carlo method. It is shown that the nearest-neighbor Coulomb
interaction enhances the charge fluctuation and it induces the anomalous state
such as charge-ordered metallic state and the triplet next-nearest-neighbor
-wave superconductivity. We discuss the relation to the real materials and
propose the unified view of the family of -(BEDT-TTF)X.Comment: 4 pages, 5 figure
Bessel bridges decomposition with varying dimension. Applications to finance
We consider a class of stochastic processes containing the classical and
well-studied class of Squared Bessel processes. Our model, however, allows the
dimension be a function of the time. We first give some classical results in a
larger context where a time-varying drift term can be added. Then in the
non-drifted case we extend many results already proven in the case of classical
Bessel processes to our context. Our deepest result is a decomposition of the
Bridge process associated to this generalized squared Bessel process, much
similar to the much celebrated result of J. Pitman and M. Yor. On a more
practical point of view, we give a methodology to compute the Laplace transform
of additive functionals of our process and the associated bridge. This permits
in particular to get directly access to the joint distribution of the value at
t of the process and its integral. We finally give some financial applications
to illustrate the panel of applications of our results
The Origin of the Charge Ordering and Its Relevance to Superconductivity in -(BEDT-TTF)X: The Effect of the Fermi Surface Nesting and the Distant Electron-Electron Interactions
The origin of the charge ordering in organic compounds -(BEDT-TTF) ((SCN), Tl,Rb,Co, Cs,Zn) is studied using an extended
Hubbard model. Calculating the charge susceptibility within random phase
approximation (RPA), we find that the charge
ordering observed at relatively high temperatures can be considered as a
consequence of a cooperation between the Fermi surface nesting, controlled by
the hopping integral in the direction, and the electron-electron
interactions, where the distant (next nearest neighbor) interactions that have
not been taken into account in most of the previous studies play an important
role.Mean field analysis at T=0 also supports the RPA results, and further
shows that in the charge ordered state, some portions of the Fermi
surface remain ungapped and are nested with a nesting vector close to the
modulation wave vector of the horizontal stripe ordering observed at low
temperatures in (SCN). We further study the possibility of
superconductivity by taking into account the distant off-site repulsions and
the band structure corresponding to I, in which superconductivity is
experimentally observed. We find that there is a close competition between
-wave-like singlet pairing and -wave-like triplet pairing due
to a cooperation between the charge and the spin fluctuations. The present
analysis provides a possible unified understanding of the experimental phase
diagram of the -(BEDT-TTF) family, ranging from a charge ordered
insulator to a superconductor.Comment: 13 pages, 18 figures (Figs.5,6,7,14,15,18 compressed using jpeg2ps
Coherence of single spins coupled to a nuclear spin bath of varying density
The dynamics of single electron and nuclear spins in a diamond lattice with
different 13C nuclear spin concentration is investigated. It is shown that
coherent control of up to three individual nuclei in a dense nuclear spin
cluster is feasible. The free induction decays of nuclear spin Bell states and
single nuclear coherences among 13C nuclear spins are compared and analyzed.
Reduction of a free induction decay time T2* and a coherence time T2 upon
increase of nuclear spin concentration has been found. For diamond material
with depleted concentration of nuclear spin, T2* as long as 30 microseconds and
T2 of up to 1.8 ms for the electron spin has been observed. The 13C
concentration dependence of T2* is explained by Fermi contact and dipolar
interactions with nuclei in the lattice. It has been found that T2 decreases
approximately as 1/n, where n is 13C concentration, as expected for an electron
spin interacting with a nuclear spin bath.Comment: 4 pages, 4 figures, 1 movie (avi), 1 supplementary material (pdf
Reversible Fluorination of Graphene: towards a Two-Dimensional Wide Bandgap Semiconductor
We report the synthesis and evidence of graphene fluoride, a two-dimensional
wide bandgap semiconductor derived from graphene. Graphene fluoride exhibits
hexagonal crystalline order and strongly insulating behavior with resistance
exceeding 10 G at room temperature. Electron transport in graphene
fluoride is well described by variable-range hopping in two dimensions due to
the presence of localized states in the band gap. Graphene obtained through the
reduction of graphene fluoride is highly conductive, exhibiting a resistivity
of less than 100 k at room temperature. Our approach provides a new
path to reversibly engineer the band structure and conductivity of graphene for
electronic and optical applications.Comment: 7 pages, 5 figures, revtex, to appear in PR
Continued fraction solution of Krein's inverse problem
The spectral data of a vibrating string are encoded in its so-called
characteristic function. We consider the problem of recovering the distribution
of mass along the string from its characteristic function. It is well-known
that Stieltjes' continued fraction provides a solution of this inverse problem
in the particular case where the distribution of mass is purely discrete. We
show how to adapt Stieltjes' method to solve the inverse problem for a related
class of strings. An application to the excursion theory of diffusion processes
is presented.Comment: 18 pages, 2 figure
Origin of Drastic Change of Fermi Surface and Transport Anomalies in CeRhIn5 under Pressure
The mechanism of drastic change of Fermi surfaces as well as transport
anomalies near P=Pc=2.35 GPa in CeRhIn5 is explained theoretically. The key
mechanism is pointed out to be the interplay of magnetic order and Ce-valence
fluctuations. We show that the antiferromagnetic state with "small" Fermi
surfaces changes to the paramagnetic state with "large" Fermi surfaces with
huge enhancement of effective mass of electrons with keeping finite c-f
hybridization. This explains the drastic change of the de Haas-van Alphen
signals. Furthermore, it is also consistent with the emergence of T-linear
resistivity simultaneous with the residual resistivity peak at P=Pc in CeRhIn5.Comment: 5 pages, 3 figures, submitted to Journal of Physical Society of Japa
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