Observations Of Ybco Superconductors Under A Low-Temperature Scanning Electron Microscope

Microscopic analyses have been performed on YBCO superconductors with Ca-doping and Gd-doping as a function of temperature by employing a low-temperature scanning electron microscope (LTSEM). On lowering temperature of the sample from 300 K to 90 K, the brightness of the SEM image changes due to the change in resistance of the sample. For the underdoped cuprates Y1-xCaxBa2Cu3O7-delta, with x = 0.2, the pseudo gap in the normal state is opened at a temperature T* which far below the ciritical temperature T-c of the superconductor. The opening of the pseudo gap has directly been observed under LTSEM (temperature fluctuating in the range of +/- 5 K). At temperature T* the formation of quasi-particles takes place, thus a sudden brightness change in the SEM image is observed. The results of these measurements are compared with the four-point probe measurement. It is proved that the data of these two measurements are quite in agreement with each other.