Abstract
The temperature dependence of the 63Cu nuclear spin-lattice relaxation rate (T1T)-1 , spin-spin relaxation rate T2G-1 and frequency spectra at the Cu(2) planar site in the normal state of YBa2Cu4O8 have been measured under high pressure by the nuclear quadrupole resonance(NQR) technique. The pseudo spin gap temperature slightly decreased with increasing pressure. It seems that the pressure effects are resembled with carrier doping effects in the increase of superconducting transition temperature Tc and NQR frequency νQ(2) and decrease of pseudo spin gap temperature. If the increase of νQ(2) under pressure was caused by introducing carrier into Cu(2) planar site, the change of pseudo spin gap temperature is generally originated in carrier concentration at Cu(2) site.
