On this day 117 years ago, on May 23, 1908 (April 24, 1908 in the lunar calendar), Nobel Laureate in Physics John Bardeen was born. John Bardeen (May 23, 1908 - January 30, 1991), an American physicist, won the Nobel Prize in Physics twice for the transistor effect and the BCS theory of superconductivity. Bardeen was born in Madison, Wisconsin, USA in 1908. He entered the Department of Electrical Engineering at the University of Wisconsin-Madison in 1923. He received his bachelor's degree in 1928 and his master's degree in 1929. After graduation, Bardeen stayed on as a research assistant in electrical engineering. From 1930 to 1933, Bardeen worked on methods for surveying the earth's magnetic field and gravity field at the Bay Experimental Institute in Pittsburgh. In 1933, Bardeen entered Princeton University, where he studied solid-state physics under the supervision of E.P. Wegener. He was a researcher at Harvard University from 1935 to 1938, and received his doctorate from Princeton University in 1936. From 1938 to 1941, Bardeen was an assistant professor at the University of Minnesota. He worked at the Naval Ordnance Laboratory in Washington from 1941 to 1945. From 1945 to 1951, he worked at the Bell Telephone Company Experimental Institute to study the conductivity mechanism and surface properties of semiconductors and metals. In 1947, he and his colleague Bratton invented the semiconductor transistor. A month later, Shockley invented the PN junction transistor. The three of them jointly won the 1956 Nobel Prize in Physics for their discovery of the transistor effect. In the early 1950s, Bardeen had already begun to consider the problem of superconductivity. He realized that the interaction between electrons and phonons was the key to solving the problem. In 1953, Schriever came to the University of Illinois and pursued a doctorate in physics under the supervision of Bardin, and chose the problem of superconductivity as the topic of his doctoral dissertation. On the recommendation of Zhenning Yang of the Institute for Advanced Study in Princeton, Cooper, who had just received his doctorate from Columbia University, began working with Bardin and Schriever. In 1957, Bardin, Cooper and Schriever co-founded the BCS theory, which provided a reasonable explanation for superconductivity. The three of them also won the 1972 Nobel Prize in Physics. Bardin also became the first and so far the only person to have won the Nobel Prize in Physics twice.