Based on measurements of the 63Cu Knight shift and the nuclear spin-lattice relaxation rate under magnetic fields up to 28 T, we find that the pseudogap in the slightly overdoped TlSr2CaCu2O6.88 (Tc=68 K) is due to Cooper pair density fluctuations. Such fluctuations are also found in the underdoped YBa2Cu4O8 (Tc=74 K), but are small and only survive up to Tsf ≃ Tc+15K=90 K, which is much lower than the field-independent pseudogap temperature T* ≃ 160 K. The implication on the phase diagram is discussed. At low temperatures in the superconducting state, a field-induced finite density of states was found in both compounds and is interpreted as due to the quasiparticles outside a vortex core in a d-wave superconductor.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering