J.F. Marucco

63Cu NMR evidence for enhanced antiferromagnetic correlations around Zn impurities in YBa2Cu3O6.7

Doping the high- T(c) superconductor YBa2Cu3O6.7 with 1.5% of nonmagnetic Zn impurities in CuO2 planes is shown to produce a considerable broadening of 63Cu NMR spectra, as well as an increase of low-energy magnetic fluctuations detected in 63Cu spin-lattice relaxation measurements. A model-independent analysis demonstrates that these effects are due to the development of staggered magnetic moments on many Cu sites around each Zn and that the Zn-induced moment in the bulk susceptibility might be explained by this staggered magnetization. Several implications of these enhanced antiferromagnetic correlations are discussed.

Synthesis and characterization of superconducting single crystals of HgBa2Ca2Cu3O8+δ

Abstract HgBa 2 Ca 2 Cu 3 O 8+δ single crystals of submillimeter size were grown in a single-step synthesis under normal pressure. The crystals were examined by X-ray diffraction, energy dispersive X-ray analysis (EDX), scanning electron microscopy and magnetic measurements. The “as-grown” single crystals have a T c of 120 K, as defined by the onset of diamagnetism. After annealing in oxygen at 300°C for 6 h, they can display a sharp superconducting transition temperature as high as 135 K.

Persistence of Li Induced Kondo Moments in the Superconducting State of Cuprates

Using 7Li NMR shift data, the anomalous local moment induced by spinless Li impurities persists below T(c) in YBa 2Cu 3O6+y. In the underdoped regime, the moments retain their Curie law below Tc. In contrast, near optimal doping, the large Kondo screening observed above Tc (TK = 135 K) is strongly reduced below Tc as expected theoretically when the superconducting gap develops. The limited spatial extent of the induced moment (on first near neighbor Cu) is not drastically modified below Tc, which allows a comparison with STM determination of the local density of states. Our results constrain theoretical models of the impurity electronic properties.

Absence of static phase separation in the high T(c) cuprate YBa(2)Cu(3)O(6+y).

We use 89Y NMR in YBa(2)Cu(3)O(6+y) in order to evaluate with high sensitivity the distribution of hole content p in the CuO2 planes. For y=1 and y=0.6, this hole doping distribution is found narrow with a full width at half maximum smaller than Deltap=0.025. This rules out any large static phase separation between underdoped and optimally doped regions in contrast with the one observed by STM in Bi2212 and by NQR in LaSrCuO. This establishes that static electronic phase separation is not a generic feature of the cuprates.

Thermodynamics of YBa2Cu3Oz

Abstract Δ G (O 2 ) and Δ H (O 2 ), respectively partial relative Gibbs free energy and enthalpy of O 2 in YBa 2 Cu 3 O z have been measured with high precision at 500, 600 and 700°C for 10 −2 ⩽ P O2 /atm⩽1. ΔG (O 2 ) has been determined by means of the equilibrium method between oxide and N 2 O 2 mixtures using a thermobalance. Δ H (O 2 ) has been measured by reaction microcalorimetry between oxide and N 2 O 2 mixtures. At the orthorhombic-to-tetragonal transition point, Δ G (O 2 ) is continuous and Δ G (O 2 ) undergoes a λ-type discontinuity which is quite coherent with the interpretation of this phase transformation as an order-disorder transition.

Synthesis, crystal structure and magnetic properties of superconducting single crystals of HgBa2CuO4+δ

Abstract Single crystals of HgBa 2 CuO 4+δ of submillimetric sizes were grown with the same one step, low pressure, gold amalgamation technique used to obtain single crystals of HgBa 2 Ca 2 Cu 3 O 8+δ . Remarkable superconducting properties are displayed by the samples which are optimally doped as grown. The sharpness of the transition profiles of the magnetic susceptibility, its anisotropy dependence and the volume fraction exhibiting the Meissner effect exceed the values obtained with the best crystal samples of Hg-1223. X-rays show that no substitutional defects have been found in the mercury plane, in particular no mixed occupancy of copper at the mercury site. The interstitial oxygen content at ( 1 2 , 1 2 , 0 ) δ = 0.066 ± 0.008 is about one third that observed in optimally doped Hg-1223, resulting in an identical doping level per CuO 2 plane in both compounds.

Antiferromagnetism in YBa2Cu3O6+x: Ga and Zn substitutions II. zero field NMR of the Cu magnetic sites

Abstract We present an extensive study of the antiferromagnetic state of YBa 2 Cu 3 O 6+ x (0 x 63 Cu zero field nuclear magnetic resonance (ZFNMR). Our experiments clearly demonstrate that hole doping in the CuO 2 planes occurs only for x > 0.2 and that the nuclear spin T 1 is very short nearby doped holes. As for static magnetic disorder, we show that ZFNMR is a very local in-plane probe nearly insensitive to the stacking of the CuO 2 antiferromagnetic sheets. No magnetic disorder occurs for x 2 planes. For x > 0.2 a comparison with muon and neutron results is presented. Cu substitution by Ga and Zn do not affect markedly the AF order of the CuO 2 sheet while intensity measurements clearly demonstrate that Zn does not substitute appreciably on the Cu(2) site.

89 Y NMR probe of Zn induced local magnetism in YBa 2 (Cu 1-y Zn y ) 3 O 6+x

Abstract:We present detailed data and analysis of the effects of Zn substitution on the planar Cu site in YBa2Cu3O6+x (YBCO6+x) as evidenced from our 89Y NMR measurements on oriented powders. For

Measurement of the phase diagram of (Y1−yCay)Ba2Cu3O6 versus calcium content: Evidence for the importance of charge dynamics in the destruction of TN

x \ll 1