The responses to the magnetic field (H) of the superconductivity and the pseudogap in the underdoped high-Tc cuprate YBa2Cu4O8 (Tc=74 K) are reported up to 23.2 T based on NMR measurements. Even though H=23.2 T reduces Tc by 19 K, no effect is seen on the normal-state pseudogap, which continues in the temperature region where the superconductivity is destroyed by the field. This suggests that the pseudogap is a consequence of strong electron correlation effects. For temperatures T ≤ 15 K, the H-and T-variation of the 63Cu nuclear spin-lattice relaxation rate (1/T1) is 1/T1 α TH and also the Knight shift increases with increasing H. We interpret our results as evidence for H-induced quasiparticle states that extend from the d-wave vortex centers with an ungapped spectrum.
ASJC Scopus subject areas
- Statistical and Nonlinear Physics
- Condensed Matter Physics