arXiv subjects

T. Imai

Publications and source records attributed to T. Imai.

62 records · Page 4Linked to original sources

arXiv2001

(63)Cu NQR Evidence for Spatial Variation of Hole Concentration in La(2-x)Sr(x)CuO(4)

We report experimental evidence for the spatial variation of hole concentration x_(hole) in the high Tc superconductor La(2-x)Sr(x)CuO(4) (0.04 <= x <= 0.16) by using (63)Cu NQR for (63)Cu isotope enriched samples. We demonstrate that the extent of the spatial variation of the local hole concentration D(x)_(hole) is reflected on (63)1/T1 and deduce the temperature dependence. D(x)_(hole) increases below 500 - 600K, and reaches values as large as D(x)_(hole)/x ~ 0.5 below ~ 150K. We estimate the length scale of the spatial variation in x_(hole) to be R_(hole) >~ 3nm from analysis of the NQR spectrum.

cond-mat.supr-con↗

arXiv2001

(13)C NMR investigation of the superconductor MgCNi_3 up to 800K

We report (13)C NMR characterization of the new superconductor MgCNi_3 (He et al., Nature (411), 54 (2001)). We found that both the uniform spin susceptibility and the spin fluctuations show a strong enhancement with decreasing temperature, and saturate below ~50K and ~20K respectively. The nuclear spin-lattice relaxation rate 1/(13)T_1T exhibits typical behaviour for isotropic s-wave superconductivity with a coherence peak below Tc=7.0K that grows with decreasing magnetic field.

cond-mat.supr-con↗

arXiv2001

17O NMR study of q=0 spin excitations in a nearly ideal S=1/2 1D Heisenberg antiferromagnet, Sr2CuO3, up to 800 K

We used 17O NMR to probe the uniform (wavevector q=0) electron spin excitations up to 800 K in Sr2CuO3 and separate the q=0 from the q=\pmπ/a staggered components. Our results support the logarithmic decrease of the uniform spin susceptibility below T ~ 0.015J, where J=2200 K. From measurement of the dynamical spin susceptibility for q=0 by the spin-lattice relaxation rate 1/T_{1}, we demonstrate that the q=0 mode of spin transport is ballistic at the T=0 limit, but has a diffusion-like contribution at finite temperatures even for T << J.

cond-mat.str-el↗

arXiv2001

Glassy Slowing of Stripe Modulation in (La,Eu,Nd)(2-x)(Sr,Ba)(x)CuO4: A Cu-63 and La-139 NQR Study Down to 350mK

We report a comprehensive Cu and La NQR study down to 350mK in the stripe phase of the hole-doped high temperature superconductors with hole concentration approximately 1/8. We observe the hyperfine broadened NQR lineshape only below 8-20K for x=1/8, indicating that the ordered moments continue to fluctuate slowly even below the temperature range where they appear static in other measurements. Detailed numerical simulations of the Zeeman perturbed Cu NQR lineshape establish that widely accepted models of periodic modulation of spin density waves with maximum moment approxiamtely 0.3mu_B can not account for the NQR lineshape. These results suggest that significant disorder exists at NQR time scales. By fitting a single model to several sets of experimental data, we deduce the spatial distribution of the spin fluctuation frequency scale and its temperature dependence. Our results indicate that as soon as charge dynamics slow down, the spin fluctuationsbegin to slow dramatically with spin stiffness approximately 200K. However, the motional narrowing feature observed in the Zeeman perturbed NQR measurements suggest that the slowing of the spin fluctuations levels off at frequencies somewhat below the NQR frequency. By extending the analysis to other hole concentrations, we find a qualitative difference above and below x=1/8.

cond-mat.supr-con↗

arXiv2000

Double Kicker system in ATF

A double kicker system which extracts the ultra-low emittance multi-bunch beam stably from ATF damping ring was developed. The performance of the system was studied comparing an orbit jitter with single kicker extraction in single bunch mode. The position jitter reduction was estimated from the analysis of the extraction orbits. The reduction was confirmed for the double kicker system within a resolution of BPMs. More precise tuning of the system with a wire scanner has been tried by changing a beta function at the second kicker to get more reduction of kick angle jitter. The results of these studies are described in detail.

physics.acc-ph↗

arXiv1999

Systematic Cu-63 NQR studies of the stripe phase in La(1.6-x)Nd(0.4)Sr(x)CuO(4) for 0.07 <= x <= 0.25

We demonstrate that the integrated intensity of Cu-63 nuclear quadrupole resonance (NQR) in La(1.6-x)Nd(0.4)Sr(x)CuO(4) decreases dramatically below the charge-stripe ordering temperature T(charge). Comparison with neutron and X-ray scattering indicates that the wipeout fraction F(T) (i.e. the missing fraction of the integrated intensity of the NQR signal) represents the charge-stripe order parameter. The systematic study reveals bulk charge-stripe order throughout the superconducting region 0.07 <= x <= 0.25. As a function of the reduced temperature t = T/T(charge), the temperature dependence of F(t) is sharpest for the hole concentration x=1/8, indicating that x=1/8 is the optimum concentration for stripe formation.

cond-mat.supr-con↗

arXiv1999

63Cu NQR evidence of dimensional crossover to anisotropic 2d regime in S= 1/2 three-leg ladder Sr2Cu3O5

We probed spin-spin correlations up to 725 K with 63Cu NQR in the S= 1/2 three-leg ladder Sr2Cu3O5. We present experimental evidence that below 300 K, weak inter-ladder coupling causes dimensional crossover of the spin-spin correlation length ξfrom quasi-1d (ξ~ 1/T) to anisotropic 2d regime (ξ\~ exp[2πρ_{s}/T], where 2πρ_{s} = 290 +/- 30 K is the effective spin stiffness). This is the first experimental verification of the renormalized classical behavior of the anisotropic non-linear sigma model in 2d, which has been recently proposed for the striped phase in high T_{c} cuprates.

cond-mat.supr-con↗

arXiv1999

Cu-63 NQR Measurement of Stripe Order Parameter in La(2-x)Sr(x)CuO(4)

We demonstrate that one can measure the charge-stripe order parameter in the hole-doped CuO(2) planes of La(1.875)Ba(0.125)CuO(4), La(1.48)Nd(0.4)Sr(0.12)CuO(4) and La(1.68)Eu(0.2)Sr(0.12)CuO(4) utilizing the wipeout effects of Cu-63 NQR. Application of the same approach to La(2-x)Sr(x)CuO(4) reveals the presence of similar stripe order for the entire underdoped superconducting regime 1/16 < x < 1/8.

cond-mat.supr-con↗