Acoustic attenuation study on the normal-state pseudogap in underdoped YBa2Cu3O7-delta

Internal friction (IF) measurement in the kHz frequency region has been per formed for underdoped YBa2Cu3O7 - delta. A rapid decrease of internal frict ion with decreasing temperature is observed at a temperature T-g (> T-c), w hich is considered as the opening of a pseudogap. Based on the feature of p seudogap described by V. J. Emery and BCS theory, a power law decrease of i nternal friction with temperature at T-g is derived and the index is estima ted, which is consistent with the experiments. The decrease of the spin-lat tice relaxation rate 1/T-1 for NMR near 150 K in the underdoped YBCO, simil ar to that of internal friction, can be explained in the same way. Furtherm ore, in view of the different phase coherence effect on IF and 1/T-1, it ca n be predicted that another decrease for internal friction will occur near T-c but not for 1/T-1. The conclusion is confirmed by the experiments. In a ddition, the reported anomaly of resistivity near T*(similar to 160 K) for the underdoped YBCO is discussed too.