Abstract
We report a nuclear quadrupole resonance (NQR) and nuclear magnetic resonance (NMR) study of the Ba isotopes, 135Ba and 137Ba, in YBa 2Cu 4O 8. The Knight shift, at 298 K, is zero indicating that no mobile charge carriers are present at the Ba site. The temperature ( T) dependence of ν Q , which is caused by thermal expansion, can be described by a power law. The electric field gradient tensor at the Ba site is in good agreement with band structure calculations. The spin-spin relaxation rate is nearly constant between 56 and 400 K. The spin-lattice relaxation mechanism is of quadrupolar origin and its T dependence can be described perfectly by a two-phonon Raman process with a Debye temperature of 185(20) K, which agrees with the thermal conductivity result. Thus, the Ba site in YBa 2Cu 4O 8 does not sense the spin fluctuations of the CuO 2 plane.
Published Version
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