The Superconducting Revolution

In 1987, Fujikura's superconductivity development began with a superconducting current of just a few amperes.

In 1911, Kamerlingh Onnes of the Netherlands was measuring the electrical resistance of mercury using liquid helium, which he had first succeeded in liquefying at the time, when he happened to notice a phenomenon in which electrical resistance suddenly became zero at -269°C (4.2K). This was the discovery of the superconductivity phenomenon. Despite being a groundbreaking discovery, no practical results were seen after that, and it was not until the 1960s that attempts were made to process superconducting materials such as Nb-Sn, Nb-Zr, and Nb-Ti into wires. The greatest strong point / feature of superconducting wires is that they can pass large currents without electrical resistance. Focusing on this, an approach was first made to realize a "powerful magnet."

The next epoch was the discovery of oxide superconductors in 1986. It all started with research on strontium titanate by Muller and Bednorz of IBM Zurich Research Laboratory. This material is a well-known insulator known as a ferroelectric, but in La-Ba-Cu-O (perovskite system), the resistance decreased around 30K and seemed to reach zero resistance below 10K. They presented this result at a conference in Germany, but no one recognized it. In April 1986, Bednorz and Muller submitted a paper to a German journal called Zeitschrift fur Physik. After this paper was published, the results were retested at least in several places around the world. Among them, Tanaka's group at the University of Tokyo identified the crystal structure of this material and confirmed the Meissner effect. They proved that superconductivity was occurring in the La-Ba-Cu-O system to a level that everyone could be sure of. The existence of superconductivity was discovered in Tanaka's laboratory on November 13, 1986. When this result was announced at the Materials Research Society in Boston on December 5th, it astonished the world, and the search for high-temperature superconductivity continued for several years. In February 1987, Y-Ba-Cu-O (a Y-based superconductor) with a transition temperature of about 90K was discovered. In a short period of time, the critical temperature (Tc) had been raised by 60K. Since then, new superconducting transition temperatures have been broken one after another, and as of 2004, the transition temperature under high pressure for mercury-based copper oxide is 160 Kelvin, the highest ever recorded.

February 1987: With the discovery of YBa2Cu3Ox superconductor (critical temperature 90K), the critical temperature exceeded liquid nitrogen temperature (77K) for the first time. Also in the same year, BiSrCaCuO-based superconductors were discovered, and many research institutes achieved a critical current density of 1 million A/cm2 on single crystal substrates, a practical level, with YBaCuO superconductors. During this time, Fujikura also attempted to develop superconducting wire. Their first product was a 1mm diameter wire made by putting YBCO superconducting powder into a stainless steel tube and sintering it. However, the superconducting current in liquid nitrogen was only at the level of a few amps.