| NMR/NQR Spectroscopy (1998) | |||||||||||||||
Abstract | |||||||||||||||
| ng in YBa 2 Cu 4 O 8 (1--2--4) around T y = 180 K [1]. The crossover, which is not a structural phase transition, involves enhanced charge fluctuations in planes and chains accompanied by a charge (hole) transfer from chain to plane. T y is relatively close to another temperature, T , which is characteristic for underdoped high--temperature superconductors and which refers to the opening of a spin gap (as seen by NMR) in the electron spin excitation spectrum. In 1--2--4, T 150 K which lies above T c = 82 K. This spin gap effect explains the strong temperature dependence of the normal state susceptibility in 1--2--4. In collaboration with M. Eremin et al. from the Kazan State University, we have argued that the spin gap effect in 1--2--4 is caused by a transition due to a charge density wave (CDW) instability [2]. The prox | |||||||||||||||
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