The Superconducting Revolution

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

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

The next milestone was the discovery of oxide superconductors in 1986. It all began with research on strontium titanate by Muller and Bednorz of the IBM Zurich Research Laboratory. This material is a well-known insulator known as a ferroelectric. However, in La-Ba-Cu-O (a perovskite system), the resistance decreased around 30 K and appeared to reach zero resistance below 10 K. They presented their results at a German conference, but they were not recognized. In April 1986, Bednorz and Muller submitted a paper to the German journal Zeitschrift fur Physik. After the paper was published, further experiments were conducted at least in several locations around the world. Among these, Tanaka's group at the University of Tokyo identified the crystalline structure of the material and confirmed the Meissner effect. This proved beyond doubt that superconductivity existed in the La-Ba-Cu-O system. The existence of superconductivity was discovered in Tanaka's lab 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) was discovered, which transitions at around 90K. In a short period of time, the critical temperature (Tc) had been raised by 60K. Since then, 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 temperature 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.