We demonstrate that one can measure the charge-stripe order parameter in the hole-doped CuO2 planes of La1.875Ba0.125CuO4, La1.48Nd0.4Sr0.12CuO4 and La1.68Eu0.2Sr0.12CuO4 utilizing the wipeout effects of 63 Cu NQR. Application of the same approach to La2−xSrxCuO4 reveals the presence of similar stripe order for the entire underdoped superconducting regime The mechanism of high T c superconductivity has been a major controversy throughout the past decade [1][2][3]. The complexity of the phase diagram for temperature T and hole concentration x makes it difficult to identify the key leading toward the superconducting mechanism. In 1995, Tranquada et al. [4-6] demonstrated that La 1.6−x Nd 0.4 Sr x CuO 4 (x ∼ 1 8 ) exhibits chargestripe order at T charge = 65 K, followed by a spinstripe order at somewhat lower temperature, T spin = 50 K. The discovery of the stripe phase [7] has added a new feature to the already complex phase diagram. Initially, some researchers speculated that the stripe order was merely a byproduct of the LTO-LTT (low temperature orthorhombic-low temperature tetragonal) structural phase transition and was extrinsic to the fundamental physics of high T c superconductivity. However, more recently, spin-stripe order was observed in La 2−x Sr x CuO 4 (x = 0.12 [8,9] , exhibits no critical divergence at the stripe transition. The origin of the elusiveness is in the glassy nature of the stripe transition [6,18,19]. In other words, the critical slowing down of spin-stripe fluctuations below T charge is more gradual than ordinary magnetic phase transitions involving only the spin degrees of freedom. As a consequence, the apparent critical temperature T spin of the spin-stripe order is lower for experimental probes with slower frequency scales, i.e. T spin = 50 K for elastic neutron scattering (

We report experimental evidence for the spatial variation of hole concentration x(hole) in the high T(c) superconductor La2-xSrxCuO4 ( 0.04 < or = x < or = 0.16) via 63Cu NQR using 63Cu isotope enriched samples. We demonstrate that the extent of the spatial variation of the local hole concentration Delta(x)hole is reflected on (63)1/T1 and deduce the temperature dependence. Delta(x)hole increases below 500-600 K, and reaches values as large as Delta(x)hole/x approximately 0.5 below approximately 150 K. We estimate the length scale of the spatial variation in x(hole) to be R(hole) greater, similar 3 nm from an analysis of the NQR spectrum.

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63 Cu and 139 La nuclear quadrupole resonance and Zeeman perturbed nuclear magnetic resonance experiments are performed on the striped phase of the high temperature superconductors La2−xBaxCuO4 and La2−x−y(Nd,Eu)ySrxCuO4. The first goal of the present study is to utilize the fact that ordered Cu magnetic moments exert a static hyperfine field on the 63 Cu and 139 La nucleii to deduce the charge density and ordered moment within the CuO2 planes. A hyperfine broadened NQR lineshape is observed in both La2−xBaxCuO4 and La1.80−xEu0.20SrxCuO4 for x ≈ 1 8 . Detailed numerical analysis of the 63 Cu NQR lineshape establishes that widely accepted models of periodic sinusoidal or square-well shaped modulations of spin density waves with maximum moment ∼ 0.3µB , as inferred from elastic neutron scattering and µSR measurements, can not account for the NQR lineshape unless we assume a relatively small ordered moment ∼ 0.15µB with a comparably large distribution. The second goal of the present work is to establish the temperature dependence of the fluctuation frequency scale of stripes. We find that the the fraction of missing 63 Cu NQR intensity below charge ordering temperature T charge accurately tracks the temperature dependence of the charge order parameter as measured by scattering methods. By fitting a single model to the temperature dependences of the wipeout fraction F (T ) for 63 Cu and 139 La NQR, the spin order parameter measured by elastic neutron scattering, and the µSR data, we deduce the spatial distribution of the spin fluctuation frequency scale Γ and its temperature dependence. These results indicate that as soon as charge dynamics slow down, the spin fluctuations begin to slow dramatically with spin stiffness 2πρ ef f s ∼ 200 K. By extending the analysis to other hole concentrations, we demonstrate a qualitative difference in the spatial variation of electronic states induced by slowing charge dynamics above and below x = 1 8 .

We used17 O 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 = ± π 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/T1, 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. 75.40.Gb, 76.60.EsThe one-dimensional Heisenberg spin chain has one of the simplest Hamiltonians, H = J i S i · S i+1 , yet our understanding of its fascinating quantum mechanical properties is still developing with recent theoretical [1][2][3][4][5][6][7][8] and experimental [9][10][11][12] studies. A recent breakthrough in experimental studies of spin chains is the identification of a nearly ideal 1D S = 1 2 Heisenberg antiferromagnet, Sr 2 CuO 3 , by Motoyama et al. [9] In this system, S = 1 2 spins reside at Cu sites, and the superexchange interaction J is mediated by hybridization with the 2p σ orbital of the in-chain O(1) site, see Fig.1(a). Based on the fit of the uniform spin susceptibility χSr 2 CuO 3 has proven to be an ideal material for the experimental studies of S = Heisenberg spin chain can be probed at unprecedently low scales of temperature and energy. The second major advantage of Sr 2 CuO 3 is that 63 Cu NMR is observable at the magnetic cation site, because the large J suppresses the nuclear relaxation rates. In a series of publications, Takigawa et al. reported detailed 63 Cu NMR investigations of the low energy spin excitations [10][11][12]. They successfully tested the theoretical predictions for the q = ± π a staggered mode in the scaling limit [2], including the low temperature logarithmic corrections to the staggered dynamical susceptibility [4]. The third major advantage of Sr 2 CuO 3 , although it has never been exploited in the earlier NMR works, is the high local symmetry of the crystal structure. The Cu-O-Cu chain is strictly straight and the in-chain O(1) site is located in the middle of adjacent Cu sites as shown in Fig.1(a). Therefore the staggered components of the magnetic hyperfine fields from Cu electron spins are canceled out at the in-chain O(1) sites. Accordingly, one can probe the low energy spin excitations for the q = 0 long wavelength mode (see Fig.1(c) 17 O NMR studies have been reported despite the rich information expected for the unexplored q = 0 mode.In this Letter, we report the first successful 17 O NMR investigation of Sr 2 CuO 3 single crystals. We accurately measured the temperature dependence of the uniform spin susceptibility χ ′ (q = 0) by NMR Knight shift at the in-chain O(1) site without suffering from the contribution by free-spins that limits the accuracy of bulk susceptibility measurements and 63 Cu NMR at low temperatures. We found that χ ′ (q = 0) decreases steeply below T ∼ 0.015J without the signature ...