758 research outputs found
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
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
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
Non-magnetic impurities in two- and three- dimensional Heisenberg antiferromagnets
In this paper we study in a large-S expansion effects of substituting spins
by non-magnetic impurities in two- and three- dimensional Heisenberg
antiferromagnets in a weak magnetic field. In particular, we demonstrate a
novel mechanism where magnetic moments are induced around non-magnetic
impurities when magnetic field is present. As a result, Curie-type behaviour in
magnetic susceptibility can be observed well below the Neel temperature, in
agreement with what is being observed in and
compounds.Comment: Latex fil
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
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
Accelerated gas-liquid visible light photoredox catalysis with continuous-flow photochemical microreactors
In this protocol, we describe the construction and use of an operationally simple photochemical microreactor for gas-liquid photoredox catalysis using visible light. The general procedure includes details on how to set up the microreactor appropriately with inlets for gaseous reagents and organic starting materials, and it includes examples of how to use it to achieve continuous-flow preparation of disulfides or trifluoromethylated heterocycles and thiols. The reported photomicroreactors are modular, inexpensive and can be prepared rapidly from commercially available parts within 1 h even by nonspecialists. Interestingly, typical reaction times of gas-liquid visible light photocatalytic reactions performed in microflow are lower (in the minute range) than comparable reactions performed as a batch process (in the hour range). This can be attributed to the improved irradiation efficiency of the reaction mixture and the enhanced gas-liquid mass transfer in the segmented gas-liquid flow regime
Structure and Unprecedented Reactivity of a Mononuclear Nonheme Cobalt(III) Iodosylbenzene Complex
A mononuclear nonheme cobalt(III) iodosylbenzene complex, [CoIII(TQA)(OIPh)(OH)]2+ (1), is synthesized and characterized structurally and spectroscopically. While 1 is a sluggish oxidant in oxidation reactions, it becomes a competent oxidant in oxygen atom transfer reactions, such as olefin epoxidation, in the presence of a small amount of proton. More interestingly, 1 shows a nucleophilic reactivity in aldehyde deformylation reaction, demonstrating that 1 has an amphoteric reactivity. Another interesting observation is that 1 can be used as an oxygen atom donor in the generation of high-valent metal-oxo complexes. To our knowledge, we present the first crystal structure of a CoIII iodosylbenzene complex and the unprecedented reactivity of metal-iodosylarene adduct
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