Pure nuclear quadrupole resonance determination of the electric field gradient asymmetry for broad lines (and application to YBa2Cu3O7)

We present an angle dependent nuclear quadrupole resonance (ADNQR) method to determine the electric field gradient asymmetry parameter eta in systems where the resonance line is so broad that the radio frequency field can excite only a portion of the nuclear spins. In this situation the recently developed spectroscopic methods are not applicable. ADNQR is useful for single crystals and oriented powders, and, for small eta determines eta^4. Therefore, it can be used to evaluate fluctuations in eta due to inhomogeneities. We demonstrate the application of ADNQR experimentally to oriented superconducting YBa2Cu3O7 powder.Comment: 5 pages, 3 figure

Charge-Inhomogeneity doping relations in YBCO detected by Angle Dependent Nuclear Quadrupole Resonance

The origin of charge inhomogeneity in YBa_{2}Cu_{3}O_{y} is investigated using a new experimental method designed to determine the nuclear quadrupole resonance (NQR) asymmetry parameter eta for very wide NQR lines at different positions on the line. The method is based on the measurement of the echo intensity as a function of the angle between the radio frequency field H1 and the principal axis of the electric field gradient. Static charge inhomogeneity deduced from eta>0 are found in this compound, but only in conjunction with oxygen deficiency. This limits considerably the possible forms of charge inhomogeneity in bulk YBa_{2}Cu_{3}O_{y}.Comment: To be published in Phys. Rev. B; Revised version with a correction to figure

Study of oxygen ordering in htc superconductors by magnetic resonance of different nuclei

NMR of 169Tm and NQR/NMR of 63/65Cu was applied to investigate the order of oxygen in the HTC superconductors of the type RBa2Cu301. From the spectra of three different lattice sites, one for Tm and two for Cu, it is evident, that three ordered structures exist: Tetra for x = 6.0, ortho-II for x = 6.5 and ortho-I for x = 7.0. No other ordered structures could be detected. A coexistence of ortho-I and -II is evident in a wide region between 6.6 and 6.8. The existence of extended domains of ortho-II is essential for the onset of superconductivity. In the tetragonal region below 6.3 we find mainly insulated oxygen ions in the Cu(1) plane; in superconducting samples of the 60 K plateau oxygen is ordered in chains of a mean length of about 12 oxygen ions. In the region of the 90 K plateau the chains become very long and the oxygen vacancies are clustered in empty fragments of chains. © 1993 IOP Publishing Ltd

Two loop renormalization of the magnetic coupling and non-perturbative sector in hot QCD

The goal of this paper is two-fold. The first aim is to present a detailed version of the computation of the two-loop renormalization of the magnetic coupling in hot QCD. The second is to compare with lattice simulations the string tension of a spatial Wilson loop using the result of our two-loop computationComment: 32 page

Cu NMR Study of Detwinned Single Crystals of Ortho--II YBCO6.5

Copper NMR has been used as a local probe of the oxygen ordering in Ortho--II YBa2Cu3O6.5 crystals grown in BaZrO3 crucibles. Line assignments have been made to each of the expected crystallographically inequivalent sites. The presence of distinct and narrow lines for these sites as well as the lack of a line known to be associated with oxygen defects indicates that these crystals are highly stoichiometric. Our estimate of the lower limit on the chain length is consistent with that derived from X-ray diffraction measurements. In addition, we have found no evidence for static magnetic moments, in contrast to some previous results.Comment: 11 pages, 7 figures, submitted to Physica

Study of oxygen ordering in htc superconductors by magnetic resonance of different nuclei

NMR of 169Tm and NQR/NMR of 63/65Cu was applied to investigate the order of oxygen in the HTC superconductors of the type RBa2Cu301. From the spectra of three different lattice sites, one for Tm and two for Cu, it is evident, that three ordered structures exist: Tetra for x = 6.0, ortho-II for x = 6.5 and ortho-I for x = 7.0. No other ordered structures could be detected. A coexistence of ortho-I and -II is evident in a wide region between 6.6 and 6.8. The existence of extended domains of ortho-II is essential for the onset of superconductivity. In the tetragonal region below 6.3 we find mainly insulated oxygen ions in the Cu(1) plane; in superconducting samples of the 60 K plateau oxygen is ordered in chains of a mean length of about 12 oxygen ions. In the region of the 90 K plateau the chains become very long and the oxygen vacancies are clustered in empty fragments of chains. © 1993 IOP Publishing Ltd

Study of oxygen ordering in htc superconductors by magnetic resonance of different nuclei

NMR of 169Tm and NQR/NMR of 63/65Cu was applied to investigate the order of oxygen in the HTC superconductors of the type RBa2Cu301. From the spectra of three different lattice sites, one for Tm and two for Cu, it is evident, that three ordered structures exist: Tetra for x = 6.0, ortho-II for x = 6.5 and ortho-I for x = 7.0. No other ordered structures could be detected. A coexistence of ortho-I and -II is evident in a wide region between 6.6 and 6.8. The existence of extended domains of ortho-II is essential for the onset of superconductivity. In the tetragonal region below 6.3 we find mainly insulated oxygen ions in the Cu(1) plane; in superconducting samples of the 60 K plateau oxygen is ordered in chains of a mean length of about 12 oxygen ions. In the region of the 90 K plateau the chains become very long and the oxygen vacancies are clustered in empty fragments of chains. © 1993 IOP Publishing Ltd

Study of oxygen ordering in htc superconductors by magnetic resonance of different nuclei

NMR of 169Tm and NQR/NMR of 63/65Cu was applied to investigate the order of oxygen in the HTC superconductors of the type RBa2Cu301. From the spectra of three different lattice sites, one for Tm and two for Cu, it is evident, that three ordered structures exist: Tetra for x = 6.0, ortho-II for x = 6.5 and ortho-I for x = 7.0. No other ordered structures could be detected. A coexistence of ortho-I and -II is evident in a wide region between 6.6 and 6.8. The existence of extended domains of ortho-II is essential for the onset of superconductivity. In the tetragonal region below 6.3 we find mainly insulated oxygen ions in the Cu(1) plane; in superconducting samples of the 60 K plateau oxygen is ordered in chains of a mean length of about 12 oxygen ions. In the region of the 90 K plateau the chains become very long and the oxygen vacancies are clustered in empty fragments of chains. © 1993 IOP Publishing Ltd