832 research outputs found
Superconductivity of the Ternary Boride Li_2Pd_3B Probed by ^{11}B NMR
We report a ^{11}B NMR measurement on the recently discovered superconductor
Li_2Pd_3B. The nuclear spin lattice relaxation rate 1/T_1 shows a well-defined
coherence peak just below T_c (H=1.46 T)=5.7 K, and the spin susceptibility
measured by the Knight shift also decreases below T_c. These results indicate
that the superconductivity is of conventional nature, with an isotropic gap.
Our results also suggest that the -electrons of boron and the d-electrons of
palladium that hybridize with boron -electrons are primarily responsible for
the superconductivity.Comment: 4 pages, 5 figure
Screening of point charge impurities in highly anisotropic metals: application to spin relaxation in underdoped cuprates
We calculate the screening charge density distribution due to a point charge,
such as that of a positive muon (), placed between the planes of a
highly anisotropic layered metal. In underdoped hole cuprates the screening
charge converts the charge density in the metallic-plane unit cells in the
vicinity of the to nearly its value in the insulating state. The
current-loop ordered state observed by polarized neutron diffraction then
vanishes in such cells, and also in nearby cells over a distance of order the
intrinsic correlation length of the loop-ordered state. This in turn strongly
suppresses the loop-current field at the site. We estimate this
suppressed field in underdoped YBaCuO and
LaSrCuO, and find consistency with the observed 0.2--0.3 G
field in the former case and the observed upper bound of 0.2 G in the
latter case. This resolves the controversy between the neutron diffraction and
SR experiments. The screening calculation also has relevance for the
effect of other charge impurities in the cuprates, such as the dopants
themselves
59Co-NQR study on superconducting NaxCoO2.yH2O
Layered Co oxide NaxCoO2.yH2O with a superconducting transition temperature
Tc =4.5 K has been studied by 59Co NQR. The nuclear spin relaxation rate 1/59T1
is nearly proportional to temperature T in the normal state. In the
superconducting state, it exhibits the coherence peak and decreases with
decreasing T below ~0.8Tc. Detailed comparison of the 1/T1T values and the
magnetic susceptibilities between NaxCoO2.yH2O and NaxCoO2 implies that the
metallic state of the former system is closer to a ferromagnetic phase than
that of the latter. These experimental results impose a restriction on the
mechanism of the superconductivity.Comment: 7 pages, 5 figures. to be published in J. Phys. Soc. Jpn. 72 (2003)
No.
Disorder, inhomogeneity and spin dynamics in f-electron non-Fermi liquid systems
Muon spin rotation and relaxation (SR) experiments have yielded evidence
that structural disorder is an important factor in many f-electron-based
non-Fermi-liquid (NFL) systems. Disorder-driven mechanisms for NFL behaviour
are suggested by the observed broad and strongly temperature-dependent SR
(and NMR) linewidths in several NFL compounds and alloys. Local disorder-driven
theories (Kondo disorder, Griffiths-McCoy singularity) are, however, not
capable of describing the time-field scaling seen in muon spin relaxation
experiments, which suggest cooperative and critical spin fluctuations rather
than a distribution of local fluctuation rates. A strong empirical correlation
is established between electronic disorder and slow spin fluctuations in NFL
materialsComment: 24 pages, 15 figures, submitted to J. Phys.: Condens. Matte
Penetration depth, multiband superconductivity, and absence of muon-induced perturbation in superconducting PrOsSb
Transverse-field muon spin rotation (SR) experiments in the
heavy-fermion superconductor PrOsSb ( K) suggest that
the superconducting penetration depth is temperature-independent
at low temperatures, consistent with a gapped quasiparticle excitation
spectrum. In contrast, radiofrequency (rf) inductive measurements yield a
stronger temperature dependence of , indicative of point nodes in
the gap. This discrepancy appears to be related to the multiband structure of
PrOsSb. Muon Knight shift measurements in PrOsSb
suggest that the perturbing effect of the muon charge on the neighboring
Pr crystalline electric field is negligibly small, and therefore is
unlikely to cause the difference between the SR and rf results.Comment: 10 pages, 7 figure
NMR investigation of vortex dynamics in Ba(Fe0.93Rh0.07)2As2 superconductor
75As NMR spin-lattice relaxation (1/T1) and spin-echo decay (1/T2) rate
measurements were performed in a single crystal of Ba(Fe0.93Rh0.07)2As2
superconductor. Below the superconducting transition temperature Tc, when the
magnetic field H is applied along the c axes, a peak in both relaxation rates
is observed. Remarkably that peak is suppressed for H || ab. Those maxima in
1/T1 and 1/T2 have been ascribed to the flux lines lattice motions and the
corresponding correlation times and pinning energy barriers have been derived
on the basis of an heuristic model. Further information on the flux lines
motion was derived from the narrowing of 75As NMR linewidth below Tc and found
to be consistent with that obtained from 1/T2 measurements. All the
experimental results are described in the framework of thermally activated
vortices motions.Comment: 8 pages, 11 figure
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