NMR and NQR study of Ca-substituted superconducting YBa{sub 2}Cu{sub 4}O{sub 8}

Journal Article · Thu Feb 01 00:00:00 EST 1996 · Physical Review, B: Condensed Matter

DOI:https://doi.org/10.1103/PhysRevB.53.3550· OSTI ID:279472

Mali, M; Roos, J; Brinkmann, D ^[1]

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1. Physik-Institut, Universitaet Zuerich, CH-8057 Zuerich (Switzerland)

We report a set of nuclear quadrupole resonance (NQR) measurements including a spin-echo double-resonance (SEDOR) experiment which provides convincing evidence that the additional chain Cu NQR line in Ca-substituted YBa{sub 2}Cu{sub 4}O{sub 8} does stem from chain Cu sites disturbed by the {open_quote}{open_quote}impurity{close_quote}{close_quote} Ca ions. From an analysis of signal intensities we conclude that {open_quote}{open_quote}impurity{close_quote}{close_quote} Ca ions, responsible for the additional line, substitute Y{sup 3+}. At high Ca doping, the concentration of the substituted Y sites, {ital x}{sup {prime}}, is appreciably smaller than the nominal Ca concentration, {ital x}. Since it is {ital x}{sup {prime}} which is responsible for a direct increase of the hole charge-carrier concentration, {ital n}, effects connected with the increase of {ital n} such as the planar Cu spin-lattice relaxation rate, the NQR frequency, and the magnetic shift are only weakly dependent on {ital x}. Thus, the substantial increase of {ital T}{sub {ital c}} with {ital x} suggests that, besides the increase of {ital n}, other effects have to play a role in the {ital T}{sub {ital c}} enhancement. One such effect might be the opening of the spin pseudogap. At 150 K, both the main and additional Cu NQR lines in nominal YBa{sub 1.9}Ca{sub 0.1}Cu{sub 4}O{sub 8} show distinctly anomalies not seen in pure YBa{sub 2}Cu{sub 4}O{sub 8} that point out the Ca doping induced structural phase transition recently observed in specific-heat, elastic-neutron-scattering, and x-ray-diffraction measurements. {copyright} {ital 1996 The American Physical Society.}

• OSTI ID: 279472
• Journal Information: Physical Review, B: Condensed Matter, Vol. 53, Issue 6; Other Information: PBD: Feb 1996
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
BARIUM OXIDES
NUCLEAR MAGNETIC RESONANCE
NUCLEAR QUADRUPOLE RESONANCE
YTTRIUM OXIDES
COPPER OXIDES
CALCIUM ADDITIONS
CALCIUM IONS
CRYSTAL DEFECTS
CRYSTAL-PHASE TRANSFORMATIONS
CUPRATES
HIGH-TC SUPERCONDUCTORS
HOLES
MAGNETIC SUSCEPTIBILITY
SPIN ECHO
SPIN-LATTICE RELAXATION
SUBSTOICHIOMETRY
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0065-0273 K
TRANSITION TEMPERATURE