5,390 research outputs found
Origin of superconducting carriers in "non-doped" T'- (La,RE)2CuO4 (RE = Sm, Eu, Gd, Tb, Lu, and Y) prepared by molecular beam epitaxy
We have performed a systematic investigation of the variations of the lattice
constants with substituent rare-earth element concentration x in the nominally
undoped superconductors T'-(La3+)2-x(RE3+)xCuO4 (RE = Sm, Eu, Gd, Tb, Lu, and
Y), which we have recently discovered using MBE. The results show both the
in-plane and out-of-plane lattice constants (a0 and c0) linearly decrease with
x, whose extrapolation to x = 2 agrees well with the reported a0 and c0 values
for each T'-RE2CuO4. This behavior is what one would expect simply from the
ionic size difference between La3+ and RE3+. The absence of the Cu-O bond
stretching due to electron-doping, which is commonly observed in electron-doped
T' and infinite-layer superconductors, implies that electron doping via oxygen
deficiencies is, at least, not a main source of charge carriers.Comment: proceedings of ISS 200
Ce doping in T-La2CuO4 films: Broken electron-hole symmetry for high-Tc superconductivity
We attempted Ce doping in La2CuO4 with the K2NiF4 (T) structure by molecular
beam epitaxy. At low growth temperature and with an appropriate substrate
choice, we found that Ce can be incorporated into the K2NiF4 lattice up to x ~
0.06, which had not yet been realized in bulk synthesis. The doping of Ce makes
T-La2-xCexCuO4 more insulating, which is in sharp contrast to Ce doping in
La2CuO4 with the Nd2CuO4 structure, which makes the compounds superconducting.
The observed smooth increase in resistivity from hole-doped side
(T-La2-xSrxCuO4) to electron-doped side (T-La2-xCexCuO4) indicates that
electron-hole symmetry is broken in the T-phase materials.Comment: proceedings of ISS 200
Phase control of La2CuO4 in thin-film synthesis
The lanthanum copper oxide, La2CuO4, which is an end member of the prototype
high-Tc superconductors (La,Sr)2CuO4 and (La,Ba)2CuO4, crystallizes in the
"K2NiF4" structure in high-temperature bulk synthesis. The crystal chemistry,
however, predicts that La2CuO4 is at the borderline of the K2NiF4 stability and
that it can crystallize in the Nd2CuO4 structure at low synthesis temperatures.
In this article we demonstrate that low-temperature thin-film synthesis
actually crystallizes La2CuO4 in the Nd2CuO4 structure. We also show that the
phase control of "K2NiF4"-type La2CuO4 versus "Nd2CuO4"-type La2CuO4 can be
achieved by varying the synthesis temperature and using different substrates.Comment: 4 pages, 5 figures, submitted to PRB, revte
Synthesis and photoemission study of as-grown superconducting MgB2 thin films
As-grown superconducting thin films of MgB2 were prepared by molecular beam
epitaxy (MBE), and studied by X-ray and ultraviolet photoelectron spectroscopy
(XPS and UPS). Only films prepared at temperatures between 150 and 320 deg.
showed superconductivity. A best TC onset of 36 K with a sharp transition width
of -1 K was obtained although the film crystallinity was poor. The in-situ
photoelectron spectra obtained on the surfaces of the MBE grown MgB2 films were
free from dirt peaks. XPS revealed that the binding energy of the Mg 2p levels
in MgB2 is close to that of metallic Mg, and the binding energy of B 1s is
close to that of transition-metal diborides. The valence UP spectra showed a
clear Fermi edge although the density of states (DOS) at EF is low and the
major components of the valence band are located between 5 and 11 eV.Comment: ISS 2001 proceedin
Computation accuracies of boundary element method and finite element method in transient eddy current analysis
The computation accuracies of the boundary-element method (BEM) and finite-element method (FEM) in transient eddy-current problems are compared by using a slot-embedded conductor model and a diffusion model that can be solved theoretically. For computing the vector potential or magnetic flux density it is shown that larger time-step width can be chosen in the BEM than in the FEM method for the same accuracy </p
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