817 research outputs found
Enhancement of electronic anomalies in iron-substituted La_2-x_Sr_x_Cu_1-y_Fe_y_O_4_ around x=0.22
We have measured the temperature dependences of Rho and Chi for
Fe-substituted La_2-x_Sr_x_Cu_1-y_Fe_y_O_4_ in the overdoped regime, in order
to investigate Fe-substitution effects on electronic properties around x=0.22.
From the Rho measurements, it has been found around x=0.22 that the values of
Rho are large at room temperature and that Rho exhibits a pronounced upturn at
low temperatures. Moreover, from the Rho and Chi measurements, it has been
found that T_c_ is anomalously depressed around x=0.22. These results indicate
that the electronic anomalies around x=0.22 are enhanced by Fe substitution,
which might be related to the development of stripe correlations by Fe
substitution.Comment: 7 pages, 3 figure
Magnetic ordering in Sr2RuO4 induced by nonmagnetic impurities
We report unusual effects of nonmagnetic impurities on the spin-triplet
superconductor Sr2RuO4. The substitution of nonmagnetic Ti4+ for Ru4+ induces
localized-moment magnetism characterized by unexpected Ising anisotropy with
the easy axis along the interlayer c direction. Furthermore, for x(Ti) > 0.03
magnetic ordering occurs in the metallic state with the remnant magnetization
along the c-axis. We argue that the localized moments are induced in the Ru4+
and/or oxygen ions surrounding Ti4+ and that the ordering is due to their
interaction mediated by itinerant Ru-4d electrons with strong spin
fluctuations.Comment: 5 pages, 4figure
Charge Localization from Local Destruction of Antiferromagnetic Correlation in Zn-doped YBa2Cu3O7-d
The in-plane normal-state resistivity of Zn-doped YBa2Cu3O7-d single crystals
is measured down to low temperatures by suppressing superconductivity with
magnetic fields up to 18 T. Substitution of Cu with Zn in the CuO2 planes is
found to induce carrier localization at low temperatures in "clean" samples
with kF l > 5, where the mean free path l is larger than the electron wave
length and thus localization is not normally expected. The destruction of the
local antiferromagnetic correlation among Cu spins by Zn is discussed to be the
possible origin of this unusual charge localization.Comment: 4 pages of LaTeX (revtex and epsf) including 4 postscript figure
Unusual T_c variation with hole concentration in Bi_2Sr_{2-x}La_xCuO_{6+\delta}
We have investigated the variation with the hole concentration in
the La-doped Bi 2201 system, BiSrLaCuO. It is
found that the Bi 2201 system does not follow the systematics in and
observed in other high- cuprate superconductors (HTSC's). The vs
characteristics are quite similar to what observed in Zn-doped HTSC's. An
exceptionally large residual resistivity component in the inplane resistivity
indicates that strong potential scatterers of charge carriers reside in CuO
planes and are responsible for the unusual variation with , as in the
Zn-doped systems. However, contrary to the Zn-doped HTSC's, the strong scatter
in the Bi 2201 system is possibly a vacancy in the Cu site.Comment: RevTeX, 3 figures, to be published in the Physical Review
59-Co and 75-As NMR Investigation of Electron-Doped High Tc Superconductor BaFe(1.8)Co(0.2)As(2) (Tc = 22K)
We report an NMR investigation of the superconductivity in BaFe(2)As(2)
induced by Co doping (Tc=22K). We demonstrate that Co atoms form an alloy with
Fe atoms and donate carriers without creating localized moments. Our finding
strongly suggests that the underlying physics of iron-pnictide superconductors
is quite different from the widely accepted physical picture of high Tc
cuprates as doped Mott insulators. We also show a crossover of electronic
properties into a low temperature pseudo-gap phase with a pseudo-gap Delta
560K, where chi(spin) constant and resisitivty T. The NMR Knight shift below Tc
decreases for both along the c-axis and ab-plane, and is consistent with the
singlet pairing scenario.Comment: Accepted for publication in J. Phys. Soc. Jpn. (4 pages
Isotope effects in underdoped cuprate superconductors: a quantum phenomenon
We show that the unusual doping dependence of the isotope effects on
transition temperature and zero temperature in - plane penetration depth
naturally follows from the doping driven 3D-2D crossover, the 2D quantum
superconductor to insulator transition (QSI) in the underdoped limit and the
change of the relative doping concentration upon isotope substitution. Close to
the QSI transition both, the isotope coefficient of transition temperature and
penetration depth approach the coefficient of the relative dopant
concentration, and its divergence sets the scale. These predictions are fully
consistent with the experimental data and imply that close to the underdoped
limit the unusual isotope effect on transition temperature and penetration
depth uncovers critical phenomena associated with the quantum superconductor to
insulator transition in two dimensions.Comment: 6 pages, 3 figure
Zn-doping effect on the magnetotransport properties of Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta} single crystals
We report the magnetotransport properties of
Bi_{2}Sr_{2-x}La_{x}Cu_{1-z}Zn_{z}O_{6+\delta} (Zn-doped BSLCO) single crystals
with z of up to 2.2%. Besides the typical Zn-doping effects on the in-plane
resistivity and the Hall angle, we demonstrate that the nature of the
low-temperature normal state in the Zn-doped samples is significantly altered
from that in the pristine samples under high magnetic fields. In particular, we
observe nearly-isotropic negative magnetoresistance as well as an increase in
the Hall coefficient at very low temperatures in non-superconducting Zn-doped
samples, which we propose to be caused by the Kondo scattering from the local
moments induced by Zn impurities.Comment: 4 pages, 4 figures, final version (one reference added), published in
Phys. Rev.
Effects of In-Plane Impurity Substitution in Sr2RuO4
We report comparative substitution effects of nonmagnetic Ti^(4+) and
magnetic Ir^(4+) impurities for Ru^(4+) in the spin-triplet superconductor
Sr2RuO4. We found that both impurities suppress the superconductivity
completely at a concentration of approximately 0.15%, reflecting the high
sensitivity to translational symmetry breaking in Sr2RuO4. In addition, a rapid
enhancement of residual resistivity is in quantitative agreement with
unitarity-limit scattering. Our result suggests that both nonmagnetic and
magnetic impurities in Sr2RuO4 act as strong potential scatterers, similar to
the nonmagnetic Zn^(2+) impurity in the high-Tc cuprates.Comment: 4 pages, 2 figures. submitted to Journal of the Physical Society of
Japa
Evolution of the resistivity anisotropy in Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta} single crystals for a wide range of hole doping
To elucidate how the temperature dependence of the resistivity anisotropy of
the cuprate superconductors changes with hole doping, both the in-plane and the
out-of-plane resistivities (\rho_{ab} and \rho_{c}) are measured in a series of
high-quality Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta} (BSLCO) single crystals for a
wide range of x (x = 0.23 - 1.02), which corresponds to the hole doping per Cu,
p, of 0.03 - 0.18. The anisotropy ratio, \rho_{c}/\rho_{ab}, shows a systematic
increase with decreasing p at moderate temperatures, except for the most
underdoped composition where the localization effect enhances \rho_{ab} and
thus lowers \rho_{c}/\rho_{ab}. The exact p dependence of \rho_{c}/\rho_{ab} at
a fixed temperature is found to be quite peculiar, which is discussed to be due
to the effect of the pseudogap that causes \rho_{c}/\rho_{ab} to be
increasingly more enhanced as p is reduced. The pseudogap also causes a rapid
growth of \rho_{c}/\rho_{ab} with decreasing temperature, and, as a result, the
\rho_{c}/\rho_{ab} value almost reaches 10^6 in underdoped samples just above
T_c. Furthermore, it is found that the temperature dependence of \rho_{c} of
underdoped samples show two distinct temperature regions in the pseudogap
phase, which suggests that the divergence of \rho_{c} below the pseudogap
temperature is governed by two different mechanisms.Comment: 10 pages, 10 figures, revised version. Discussions are expanded with
a new analysis of the T-dependence of \rho_{c} and the resulting new phase
diagra
Spin Dynamics near the Superconductor-to-Insulator Transition in Impurity-Doped YBa2Cu4O8
We studied low-frequency spin dynamics near the impurity-induced
superconductor-to-insulator transition for underdoped high-Tc superconductor
YBa2(Cu1-xMx)4O8 (M=Ni, Zn) using the Cu nuclear quadrupole resonance (NQR)
spin-echo technique. We observed remarkable suppression of the normal-state
pseudo spin-gap and a loss of Cu NQR spectrum intensity at low temperatures
around the critical impurity concentration.Comment: 6 pages, 4 figures. To be published in J. Phys. Soc. Jpn. Vol.70,
No.7 (2001
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