Thumbnail
Access Restriction
Open

Author Mali, M. ♦ Roos, J. ♦ Brinkmann, D.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword 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
Abstract 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.}
ISSN 01631829
Educational Use Research
Learning Resource Type Article
Publisher Date 1996-02-01
Publisher Place United States
Journal Physical Review, B: Condensed Matter
Volume Number 53
Issue Number 6


Open content in new tab

   Open content in new tab