1,366 research outputs found
Generic phase diagram of "electron-doped" T' cuprates
We investigated the generic phase diagram of the electron doped
superconductor, Nd2-xCexCuO4, using films prepared by metal organic
decomposition. After careful oxygen reduction treatment to remove interstitial
Oap atoms, we found that the Tc increases monotonically from 24 K to 29 K with
decreasing x from 0.15 to 0.00, demonstrating a quite different phase diagram
from the previous bulk one. The implication of our results is discussed on the
basis of tremendous influence of Oap "impurities" on superconductivity and also
magnetism in T' cuprates. Then we conclude that our result represents the
generic phase diagram for oxygen-stoichiometric Nd2-xCexCuO4.Comment: 12 pages, 4 figures; International Symposium on Superconductivity
(ISS) 200
Efficient method for simulating quantum electron dynamics under the time dependent Kohn-Sham equation
A numerical scheme for solving the time-evolution of wave functions under the
time dependent Kohn-Sham equation has been developed. Since the effective
Hamiltonian depends on the wave functions, the wave functions and the effective
Hamiltonian should evolve consistently with each other. For this purpose, a
self-consistent loop is required at every time-step for solving the
time-evolution numerically, which is computationally expensive. However, in
this paper, we develop a different approach expressing a formal solution of the
TD-KS equation, and prove that it is possible to solve the TD-KS equation
efficiently and accurately by means of a simple numerical scheme without the
use of any self-consistent loops.Comment: 5 pages, 3 figures. Physical Review E, 2002, in pres
Two-stage spin-flop transitions in S = 1/2 antiferromagnetic spin chain BaCu_2Si_2O_7
Two-stage spin-flop transitions are observed the in quasi-one-dimensional
antiferromagnet, BaCuSiO. A magnetic field applied along the
easy axis induces a spin-flop transition at 2.0 T followed by a second
transition at 4.9 T. The magnetic susceptibility indicates the presence of
Dzyaloshinskii-Moriya (DM) antisymmetric interactions between the intrachain
neighboring spins. We discuss a possible mechanism whereby the geometrical
competition between DM and interchain interactions, as discussed for the
two-dimensional antiferromagnet LaCuO, causes the two-stage
spin-flop transitions.Comment: 5 pages, 3 figures (included), accepted for publication in Phys. Rev.
Let
Spin-Peierls instability in a quantum spin chain with Dzyaloshinskii-Moriya interaction
We analysed the ground state energy of some dimerized spin-1/2 transverse XX
and Heisenberg chains with Dzyaloshinskii-Moriya (DM) interaction to study the
influence of the latter interaction on the spin-Peierls instability. We found
that DM interaction may act either in favour of the dimerization or against it.
The actual result depends on the dependence of DM interaction on the distortion
amplitude in comparison with such dependence for the isotropic exchange
interaction.Comment: 12 pages, latex, 3 figure
Far-infrared and submillimeter-wave conductivity in electron-doped cuprate La_{2-x}Ce_xCuO_4
We performed far-infrared and submillimeter-wave conductivity experiments in
the electron-doped cuprate La_{2-x}Ce_xCuO_4 with x = 0.081 (underdoped regime,
T_c = 25 K). The onset of the absorption in the superconducting state is
gradual in frequency and is inconsistent with the isotropic s-wave gap.
Instead, a narrow quasiparticle peak is observed at zero frequency and a second
peak at finite frequencies, clear fingerprints of the conductivity in a d-wave
superconductor. A far-infrared conductivity peak can be attributed to 4Delta_0,
or to 2Delta_0 + Delta_spin, where Delta_spin is the resonance frequency of the
spin-fluctuations. The infrared conductivity as well as the suppression of the
quasiparticle scattering rate below T_c are qualitatively similar to the
results in the hole-doped cuprates.Comment: 5 pages, 4 figures include
Electron transport in Coulomb- and tunnel-coupled one-dimensional systems
We develop a linear theory of electron transport for a system of two
identical quantum wires in a wide range of the wire length L, unifying both the
ballistic and diffusive transport regimes. The microscopic model, involving the
interaction of electrons with each other and with bulk acoustical phonons
allows a reduction of the quantum kinetic equation to a set of coupled
equations for the local chemical potentials for forward- and backward-moving
electrons in the wires. As an application of the general solution of these
equations, we consider different kinds of electrical contacts to the
double-wire system and calculate the direct resistance, the transresistance, in
the presence of tunneling and Coulomb drag, and the tunneling resistance. If L
is smaller than the backscattering length l_P, both the tunneling and the drag
lead to a negative transresistance, while in the diffusive regime (L >>l_P) the
tunneling opposes the drag and leads to a positive transresistance. If L is
smaller than the phase-breaking length, the tunneling leads to interference
oscillations of the resistances that are damped exponentially with L.Comment: Text 14 pages in Latex/Revtex format, 4 Postscript figure
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