4,223 research outputs found
Magnetic Penetration Depth Measurements of PrCeCuO Films on Buffered Substrates: Evidence for a Nodeless Gap
We report measurements of the inverse squared magnetic penetration depth,
, in PrCeCuO () superconducting films grown on SrTiO (001) substrates coated with a
buffer layer of insulating PrCuO. , and
normal-state resistivities of these films indicate that they are clean and
homogeneous. Over a wide range of Ce doping, ,
at low is flat: it changes by less than 0.15% over a
factor of 3 change in , indicating a gap in the superconducting density of
states. Fits to the first 5% decrease in produce values of
the minimum superconducting gap in the range of .Comment: 4 pages 5 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
On the peak in the far-infrared conductivity of strongly anisotropic cuprates
We investigate the far-infrared and submillimeter-wave conductivity of
electron-doped La_(2-x)Ce_xCuO_4 tilted 1 degree off from the ab-plane. The
effective conductivity measured for this tilt angle reveals an intensive peak
at finite frequency (\nu ~ 50 cm{-1}) due to a mixing of the in-plane and
out-of-plane responses. The peak disappears for the pure in-plane response and
transforms to the Drude-like contribution. Comparative analysis of the mixed
and the in-plane contributions allows to extract the c-axis conductivity which
shows a Josephson plasma resonance at 11.7 cm{-1} in the superconducting state.Comment: 4 pages, 4 figures include
Observation of Andreev bound states in bicrystal grain-boundary Josephson junctions of the electron doped superconductor LaCeCuO
We observe a zero-bias conductance peak (ZBCP) in the ab-plane quasiparticle
tunneling spectra of thin film grain-boundary Josephson junctions made of the
electron doped cuprate superconductor LaCeCuO. An applied magnetic field
reduces the spectral weight around zero energy and shifts it non-linearly to
higher energies consistent with a Doppler shift of the Andreev bound states
(ABS) energy. For all magnetic fields the ZBCP appears simultaneously with the
onset of superconductivity. These observations strongly suggest that the ZBCP
results from the formation of ABS at the junction interfaces, and,
consequently, that there is a sign change in the symmetry of the
superconducting order parameter of this compound consistent with a d-wave
symmetry.Comment: 9 pages, 7 figures; December 2004, accepted for publication in Phys.
Rev.
Synthesis of infinite-layer LaNiO2 films by metal-organic deposition
We report the synthesis of infinite-layer LaNiO2 thin films by metal organic
decomposition. Our work is aimed to synthesize perovskite-like oxides with 3d9
electronic configuration, which is common to high-Tc copper oxides. The 3d9
configuration is very rare in oxides other than cuprates. Ni1+ oxides, even
though Ni1+ is an unusual oxidation state, may be one of very few candidates.
One example of the Ni1+ phases is infinite-layer LaNiO2. The bulk synthesis of
LaNiO2 is difficult, but we demonstrate in this article that the thin-film
synthesis of LaNiO2 by metal organic decomposition is rather easy. This is due
to the advantage of thin films with a large-surface-to-volume ratio, which
makes oxygen diffusion prompt. Resistivity measurements indicate that LaNiO2 is
essentially a metal but unfortunately with no trace of superconductivity yet.Comment: 13 pages, 4 figure
Metal-insulator transition and the Pr/Pr valence shift in (PrY)CaCoO
The magnetic, electric and thermal properties of the
(Y)CaCoO perovskites (~=~Pr, Nd) were
investigated down to very low temperatures. The main attention was given to a
peculiar metal-insulator transition, which is observed in the praseodymium
based samples with and 0.15 at and 132~K, respectively.
The study suggests that the transition, reported originally in
PrCaCoO, is not due to a mere change of cobalt ions from
the intermediate- to the low-spin states, but is associated also with a
significant electron transfer between Pr and Co/Co sites,
so that the praseodymium ions occur below in a mixed
Pr/Pr valence. The presence of Pr ions in the insulating
phase of the yttrium doped samples (PrY)CaCoO
is evidenced by Schottky peak originating in Zeeman splitting of the ground
state Kramers doublet. The peak is absent in pure PrCaCoO
in which metallic phase, based solely on non-Kramers Pr ions, is
retained down to the lowest temperature.Comment: 10 figure
Development of a low-mass and high-efficiency charged particle detector
We developed a low-mass and high-efficiency charged particle detector for an
experimental study of the rare decay . The
detector is important to suppress the background with charged particles to the
level below the signal branching ratio predicted by the Standard Model
(O(10)). The detector consists of two layers of 3-mm-thick plastic
scintillators with wavelength shifting fibers embedded and Multi Pixel Photon
Counters for readout. We manufactured the counter and evaluated the performance
such as light yield, timing resolution, and efficiency. With this design, we
achieved the inefficiency per layer against penetrating charged particles to be
less than , which satisfies the requirement of the KOTO
experiment determined from simulation studies.Comment: 20 pages, 18 figure
- …