19,876 research outputs found
Effects of annealing and strain on La_{1-x}Ca_{x}MnO_{3} thin films: a new phase diagram in the ferromagnetic region
Oriented, single phase thin films of La_{1-x}Ca_{x}MnO_{3} have been
deposited onto (100)-oriented LaAlO_{3} (0.1<x<0.5) substrates using the Pulsed
Laser Deposition technique. While for some compositions the physical properties
(transport and magnetization) of the as-grown films are higher than the bulk
values, for other calcium contents the optimized properties are obtained only
after annealing under oxygen. These data can be partly explained by changes in
oxygen content, resulting in cationic vacancies and thus self-doping effects -
accompanying structural changes, may be the cause of properties beyond the
phase diagram. We propose a new phase diagram for
(La_{1-x}Ca_{x})_{1-y}\square_{y}MnO_{3} (0.1<x<0.5) thin films.Comment: 8 pages, 5 figures submitted to Applied Physics Letter
Evidence for a quantum phase transition in electron-doped PrCeCuO from Thermopower measurements
The evidence for a quantum phase transition under the superconducting dome in
the high- cuprates has been controversial. We report low temperature
normal state thermopower(S) measurements in electron-doped
PrCeCuO as a function of doping (x from 0.11 to
0.19). We find that at 2K both S and S/T increase dramatically from x=0.11 to
0.16 and then saturate in the overdoped region. This behavior has a remarkable
similarity to previous Hall effect results in
PrCeCuO . Our results are further evidence for an
antiferromagnetic to paramagnetic quantum phase transition in electron-doped
cuprates near x=0.16.Comment: 4 pages, 5 figure
c-Axis longitudinal magnetoresistance of the electron-doped superconductor Pr1.85Ce0.15CuO4
We report c-axis resistivity and longitudinal magnetoresistance measurements
of superconducting Pr1.85Ce0.15CuO4 single crystals. In the temperature range
13K<T<32K, a negative magnetoresistance is observed at fields just above Hc2.
Our studies suggest that this negative magnetoresistance is caused by
superconducting fluctuations. At lower temperatures (T<13K), a different
magnetoresistance behavior and a resistivity upturn are observed, whose origin
is still unknown.Comment: Accepted for publication in Phys. Rev.
The effect of substrate induced strain on the charge-ordering transition in Nd_{0.5}Sr_{0.5}MnO_{3} thin films
We report the synthesis and characterization of Nd_{0.5}Sr_{0.5}MnO_{3} thin
films grown by the Pulsed Laser Deposition technique on 100 -oriented LaAlO_{3}
substrates. X-ray diffraction (XRD) studies show that the films are 101
-oriented, with a strained and quasi-relaxed component, the latter increasing
with film thickness. We observe that transport properties are strongly
dependent on the thickness of the films. Variable temperature XRD down to 100 K
suggests that this is caused by substrate induced strain on the films.Comment: 3 pages REVTeX, 4 figures included, submitted to AP
Comment on "Spectroscopic Evidence for Multiple Order Parameter Components in the Heavy Fermion Superconductor CeCoIn"
Recently, Rourke et al. reported point-contact spectroscopy results on the
heavy-fermion superconductor CeCoIn [1]. They obtained conductance spectra
on the c-axis surfaces of CeCoIn single crystals. Their major claims are
two-fold: CeCoIn has i) d-wave pairing symmetry and ii) two coexisting
order parameter components. In this Comment, we show that these claims are not
warranted by the data presented. [1] Rourke et al., Phys. Rev. Lett. 94, 107005
(2005).Comment: accepted for publication in Phys. Rev. Lett., final for
Coexistence of Antiferromagnetism and Superconductivity in Electron-doped High-Tc Superconductors
We present magnetotransport evidence for antiferromagnetism in films of the
electron-doped cuprates PrCeCuO. Our results show clear
signature of static antiferromagnetism up to optimal doping x=0.15, with a
quantum phase transition close to x=0.16, and a coexistence of static
antiferromagnetism and superconductivity for 0.12x0.15
Point-contact spectroscopy in heavy-fermion superconductors
We develop a minimal model to calculate point-contact spectra between a
metallic tip and a superconducting heavy-fermion system. We apply our tunneling
model to the heavy fermion CeCoIn5, both in the normal and superconducting
state. In point-contact and scanning tunneling spectroscopy many heavy-fermion
materials, like CeCoIn5, exhibit an asymmetric differential conductance, dI/dV,
combined with a strongly suppressed Andreev reflection signal in the
superconducting state. We argue that both features may be explained in terms of
a multichannel tunneling model in the presence of localized states near the
interface. We find that it is not sufficient to tunnel into two itinerant bands
of light and heavy electrons to explain the Fano line shape of the differential
conductance. Localized states in the bulk or near the interface are an
essential component for quantum interference to occur when an electron tunnels
from the metallic tip of the point contact into the heavy-fermion system.Comment: 13 pages, 9 figures. Accepted for publication in Physical Review
Normal State Nernst Effect in Electron-doped Pr2-xCexCuO4: Superconducting Fluctuations and Two-band Transport
We report a systematic study of normal state Nernst effect in the
electron-doped cuprates PrCeCuO over a wide range of
doping (0.050.21) and temperature. At low temperatures, we
observed a notable vortex Nernst signal above T in the underdoped films,
but no such normal state vortex Nernst signal is found in the overdoped region.
The superconducting fluctuations in the underdoped region are most likely
incoherent phase fluctuations as found in hole-doped cuprates. At high
temperatures, a large normal state Nernst signal is found at dopings from
slightly underdoped to highly overdoped. Combined with normal state
thermoelectric power, Hall effect and magnetoresistance measurements, the large
Nernst effect is compatible with two-band model. For the highly overdoped
films, the large Nernst effect is anomalous and not explainable with a simple
hole-like Fermi surface seen in photoemission experiments.Comment: 9 pages, 8 figures, accepted in PR
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