5,768 research outputs found
Combined Pricing and Portfolio Option Procurement
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90569/1/poms1255.pd
Structural and transport properties of epitaxial NaxCoO2 thin films
We have studied structural and transport properties of epitaxial NaxCoO2 thin
films on (0001) sapphire substrate prepared by topotaxially converting an
epitaxial Co3O4 film to NaxCoO2 with annealing in Na vapor. The films are c
axis oriented and in-plane aligned with [10 1 0] NaxCoO2 rotated by 30 degrees
from [10 1 0] sapphire. Different Na vapor pressures during the annealing
resulted in films with different Na concentrations, which showed distinct
transport properties
Two-dimensional universal conductance fluctuations and the electron-phonon interaction of topological surface states in Bi2Te2Se nanoribbons
The universal conductance fluctuations (UCFs), one of the most important
manifestations of mesoscopic electronic interference, have not yet been
demonstrated for the two-dimensional surface state of topological insulators
(TIs). Even if one delicately suppresses the bulk conductance by improving the
quality of TI crystals, the fluctuation of the bulk conductance still keeps
competitive and difficult to be separated from the desired UCFs of surface
carriers. Here we report on the experimental evidence of the UCFs of the
two-dimensional surface state in the bulk insulating Bi2Te2Se nanoribbons. The
solely-B\perp-dependent UCF is achieved and its temperature dependence is
investigated. The surface transport is further revealed by weak
antilocalizations. Such survived UCFs of the topological surface states result
from the limited dephasing length of the bulk carriers in ternary crystals. The
electron-phonon interaction is addressed as a secondary source of the surface
state dephasing based on the temperature-dependent scaling behavior
Pairing in the iron arsenides: a functional RG treatment
We study the phase diagram of a microscopic model for the superconducting
iron arsenides by means of a functional renormalization group. Our treatment
establishes a connection between a strongly simplified two-patch model by
Chubukov et al. and a five-band- analysis by Wang et al.. For a wide parameter
range, the dominant pairing instability occurs in the extended s-wave channel.
The results clearly show the relevance of pair scattering between electron and
hole pockets. We also give arguments that the phase transition between the
antiferromagnetic phase for the undoped system and the superconducting phase
may be first order
Coexistence of Itinerant Electrons and Local Moments in Iron-Based Superconductors
In view of the recent experimental facts in the iron-pnictides, we make a
proposal that the itinerant electrons and local moments are simultaneously
present in such multiband materials. We study a minimal model composed of
coupled itinerant electrons and local moments to illustrate how a consistent
explanation of the experimental measurements can be obtained in the leading
order approximation. In this mean-field approach, the spin-density-wave (SDW)
order and superconducting pairing of the itinerant electrons are not directly
driven by the Fermi surface nesting, but are mainly induced by their coupling
to the local moments. The presence of the local moments as independent degrees
of freedom naturally provides strong pairing strength for superconductivity and
also explains the normal-state linear-temperature magnetic susceptibility above
the SDW transition temperature. We show that this simple model is supported by
various anomalous magnetic properties and isotope effect which are in
quantitative agreement with experiments.Comment: 7 pages, 4 figures; an expanded versio
Competitions of magnetism and superconductivity in FeAs-based materials
Using the numerical unrestricted Hartree-Fock approach, we study the ground
state of a two-orbital model describing newly discovered FeAs-based
superconductors. We observe the competition of a mode spin-density
wave and the superconductivity as the doping concentration changes. There might
be a small region in the electron-doping side where the magnetism and
superconductivity coexist. The superconducting pairing is found to be spin
singlet, orbital even, and mixed s + d wave (even
parity).Comment: 5 pages, 3 figure
Partial wave analysis of J/psi to p pbar pi0
Using a sample of 58 million events collected with the BESII
detector at the BEPC, more than 100,000 events are
selected, and a detailed partial wave analysis is performed. The branching
fraction is determined to be . A long-sought `missing' , first observed in , is observed in this decay too, with mass and width of
MeV/c and MeV/c,
respectively. Its spin-parity favors . The masses, widths, and
spin-parities of other states are obtained as well.Comment: Add one author nam
In situ epitaxial MgB2 thin films for superconducting electronics
A thin film technology compatible with multilayer device fabrication is
critical for exploring the potential of the 39-K superconductor magnesium
diboride for superconducting electronics. Using a Hybrid Physical-Chemical
Vapor Deposition (HPCVD) process, it is shown that the high Mg vapor pressure
necessary to keep the MgB phase thermodynamically stable can be achieved
for the {\it in situ} growth of MgB thin films. The films grow epitaxially
on (0001) sapphire and (0001) 4H-SiC substrates and show a bulk-like of
39 K, a (4.2K) of A/cm in zero field, and a
of 29.2 T in parallel magnetic field. The surface is smooth with a
root-mean-square roughness of 2.5 nm for MgB films on SiC. This deposition
method opens tremendous opportunities for superconducting electronics using
MgB
Topological semimetal in a fermionic optical lattice
Optical lattices play a versatile role in advancing our understanding of
correlated quantum matter. The recent implementation of orbital degrees of
freedom in chequerboard and hexagonal optical lattices opens up a new thrust
towards discovering novel quantum states of matter, which have no prior analogs
in solid state electronic materials. Here, we demonstrate that an exotic
topological semimetal emerges as a parity-protected gapless state in the
orbital bands of a two-dimensional fermionic optical lattice. The new quantum
state is characterized by a parabolic band-degeneracy point with Berry flux
, in sharp contrast to the flux of Dirac points as in graphene. We
prove that the appearance of this topological liquid is universal for all
lattices with D point group symmetry as long as orbitals with opposite
parities hybridize strongly with each other and the band degeneracy is
protected by odd parity. Turning on inter-particle repulsive interactions, the
system undergoes a phase transition to a topological insulator whose
experimental signature includes chiral gapless domain-wall modes, reminiscent
of quantum Hall edge states.Comment: 6 pages, 3 figures and Supplementary Informatio
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