23,314 research outputs found
Weak coupling d-wave BCS superconductivity and unpaired electrons in overdoped La_{2-x}Sr_{x}CuO_{4} single crystals
The low-temperature specific heat (SH) of overdoped La_{2-x}Sr_{x}CuO_{4}
single crystals (0.178=<x=<0.290) has been measured. For the superconducting
samples (0.178=<x=<0.238), the derived gap values (without any adjusting
parameters) approach closely onto the theoretical prediction
\Delta_{0}=2.14k_{B}T_{c} for the weak-coupling d-wave BCS superconductivity.
In addition, the residual term \gamma(0) of SH at H=0 increases with x
dramatically when beyond x~0.22, and finally evolves into the value of a
complete normal metallic state at higher doping levels, indicating growing
amount of unpaired electrons. We argue that this large \gamma(0) cannot be
simply attributed to the pair breaking induced by the impurity scattering,
instead the phase separation is possible.Comment: 6 pages, 6 figures; Contents added; Accepted for publication in Phys.
Rev.
Gapless Fermions and Quantum Order
Using 2D quantum spin-1/2 model as a concrete example, we studied the
relation between gapless fermionic excitations (spinons) and quantum orders in
some spin liquid states. Using winding number, we find the projective symmetry
group that characterizes the quantum order directly determines the pattern of
Fermi points in the Brillouin zone. Thus quantum orders provide an origin for
gapless fermionic excitations.Comment: 23 pages. LaTeX. Homepage http://dao.mit.edu/~we
Quantum Hall Ferromagnets
It is pointed out recently that the quantum Hall states in bilayer
systems behave like easy plane quantum ferromagnets. We study the
magnetotransport of these systems using their ``ferromagnetic" properties and a
novel spin-charge relation of their excitations. The general transport is a
combination of the ususal Hall transport and a time dependent transport with
time average. The latter is due to a phase slippage process in
and is characterized by two topological constants. (Figures will be
provided upon requests).Comment: 4 pages, Revtex, Ohio State Universit
Large single crystal growth of BaFe1.87Co0.13As2 using a nucleation pole
Co-doped iron arsenic single crystal of BaFe1.87Co0.13As2 with dimension up
to 20 x 10 x 2 mm3 were grown by a nucleation pole: an alumina stick served as
nucleation center during growth. The high quality of crystalline was
illustrated by the measurements of neutron rocking curve and X-ray diffraction
pattern. A very sharp superconducting transition temperature Tc~25 K was
revealed by both resistivity and susceptibility measurements. A nearly 100%
shielding fraction and bulk nature of the superconductivity for the single
crystal were confirmed using magnetic susceptibility data.Comment: 4 pages, 5 figure
A multiple exp-function method for nonlinear differential equations and its application
A multiple exp-function method to exact multiple wave solutions of nonlinear
partial differential equations is proposed. The method is oriented towards ease
of use and capability of computer algebra systems, and provides a direct and
systematical solution procedure which generalizes Hirota's perturbation scheme.
With help of Maple, an application of the approach to the dimensional
potential-Yu-Toda-Sasa-Fukuyama equation yields exact explicit 1-wave and
2-wave and 3-wave solutions, which include 1-soliton, 2-soliton and 3-soliton
type solutions. Two cases with specific values of the involved parameters are
plotted for each of 2-wave and 3-wave solutions.Comment: 12 pages, 16 figure
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