Microscopy in the Investigation of High-temperature

1 S U P E R C O N D U C T O R S INTRODUCTION Superconductivity is a phenomena displayed by certain metallic and ceramic materials whose electrical resistance falls to zero at a specific critical temperature. Unfortunately, until very recently, the temperatures were so cold that they were attainable only with the use of liquid helium. In 1986, IBM researchers Georg Bednorz and Alex Müller reported a new ceramic material developed from the oxides of lanthanum, barium, and copper that displayed the superconductivity effect at the (then) astonishingly high temperature of 30K. Prior to this discovery, the highest critical temperature described, 23.3K by niobium-germanium thin films, had gone unchallenged for more than a dozen years. This produced an almost explosive growth in the field as everybody hopped on the bandwagon in the race to discover new high temperature ceramic superconductors. Almost immediately, the critical temperature was raised to 40K and under high pressures, ceramics were found that superconducted at 50K. In march of 1987 Paul Chu and his coworkers (2) reported a yttrium-bariumcopper oxide ceramic that had a critical temperature of about 90K, a temperature accessible with relatively cheap liquid nitrogen. Soon, other ceramics were reported where the yttrium ion was replaced with a variety of rare-earth elements. It seemed at the time that a critical M I C R O S C O P Y I N THE INVESTIGATION OF HIGH-TEMPERATURE S U P E R C O N D U C T O R S