Phase coherence effect on the normal state internal friction in underdoped YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7-δ</inf>

Abstract

Internal friction (IF) measurement in the kilohertz frequency region has been performed for underdoped YBa 2 Cu 3 O 7-δ . A rapid decrease of IF with decreasing temperature is observed at a temperature T g ( > T c ), which is considered as the opening of pseudogap. Based on the feature of pseudogap described by V.J. Emery and the BCS theory, a power-law decrease of IF with temperature at T g is derived and the estimated index is found to be consistent with the experimental results. The decrease of the spin-lattice relaxation rate 1/T 1 for NMR near 150 K in the underdoped YBCO, similar to that of IF, can be explained in the same way. Furthermore, in view of the different phase coherence effects on IF and 1/T 1 , it can be predicted that another decrease in IF will occur near T c but not for 1/T 1 . This conclusion is confirmed by the experiments.