of the superconducting phase into a non superconducting phase application_number US 23497688 A description in fig1 the 100 surface of a strontium titanate substrate 1 which is 15 u00d7 15 mm in size was employed as a substrate surface for a thin film 2 of y 1 ba 1 9 cu 2 8 o x formed on the substrate to 0 7 u03bcm in thickness by rf magnetron sputtering the sputtering atmosphere was a mixed gas of argon and oxygen containing 50 of oxygen at a pressure of 8 u00d7 10 2 torr and the substrate temperature was 650 u00b0 c the thin film 2 thus obtained was subjected to heat treatment with the substrate 1 in flowing oxygen at 920 u00b0 c for two hours to convert the film 2 into a superconducting state a nd yag laser of 1 06 u03bcm in wavelength was employed to scan the film 2 with a laser beam 3 as shown in fig1 to thereby define a part 4 exposed to the laser beam 3 under conditions of laser power of 100 w cm 2 a scanning speed of 1 mm sec and a laser beam spot diameter of 100 u03bcm in an atmosphere of air the exposed part 4 is illustrated in a hatched manner in fig1 a platinum rhodium thermocouple was placed in proximity to the exposed part 4 to measure its temperature the result was 2000 u00b0 c then as shown in fig2 a film 2 was scanned 50 times with a laser beam at intervals of 100 u03bcm to define an exposed part.