# Leo Esaki

Reona Esaki (江崎 玲於奈 Esaki Reona, born March 12, 1925), also known as Leo Esaki, is a Japanese physicist who shared the Nobel Prize in Physics in 1973 with Ivar Giaever and Brian David Josephson for his work in electron tunneling in semiconductor materials which finally led to his invention of the Esaki diode, which exploited that phenomenon. This research was done when he was with Tokyo Tsushin Kogyo (now known as Sony). He has also contributed in being a pioneer of the semiconductor superlattices.

## Early life and education

Esaki was born in Takaida-mura, Nakakawachi-gun, Osaka Prefecture (now part of Higashiōsaka City) and grew up in Kyoto. He attended Doshisha Junior High School, then the Third Higher School. After graduating, he studied physics at Tokyo Imperial University (now the University of Tokyo), where he attended Hideki Yukawa's course in nuclear theory. He experienced the Bombing of Tokyo while at university.
Esaki received his BSc and PhD in 1947 and 1959, respectively, from the University of Tokyo (UTokyo).

## Career
### Esaki diode

From 1947 to 1960, Esaki joined Kawanishi Corporation (now Denso Ten) and Tokyo Tsushin Kogyo (now Sony). Meanwhile, American physicists John Bardeen, Walter Brattain, and William Shockley invented the transistor, which encouraged Esaki to change fields from vacuum tube to heavily-doped germanium and silicon research in Sony. One year later, he recognized that when the PN junction width of germanium is thinned, the current-voltage characteristic is dominated by the influence of the tunnel effect and, as a result, he discovered that as the voltage is increased, the current decreases inversely, indicating negative resistance. This discovery was the first demonstration of solid tunneling effects in physics, and it was the birth of new electronic devices in electronics called Esaki diode (or tunnel diode), the first quantum electronic device invention in history. He received a doctorate degree from UTokyo due to this breakthrough invention in 1959.
In 1973, Esaki was awarded the Nobel Prize for research conducted around 1958 regarding electron tunneling in solids. He became the first Nobel laureate to receive the prize from the hands of the King Carl XVI Gustaf.

### Semiconductor superlattice

Esaki moved to the United States in 1960 and joined the IBM T. J. Watson Research Center, where he became an IBM Fellow in 1967. He predicted that semiconductor superlattices will be formed to induce a differential negative-resistance effect via an artificially one-dimensional periodic structural changes in semiconductor crystals. His unique "molecular beam epitaxy" thin-film crystal growth method can be regulated quite precisely in ultrahigh vacuum. His first paper on the semiconductor superlattice was published in 1970. A 1987 comment by Esaki regarding the original paper notes:
   "The original version of the paper was rejected for publication by Physical Review on the referee's unimaginative assertion that it was 'too speculative' and involved 'no new physics.' However, this proposal was quickly accepted by the Army Research Office..."
In 1972, Esaki realized his concept of superlattices in III-V group semiconductors, later the concept influenced many fields like metals, and magnetic materials. He was elected as a member into the National Academy of Engineering for contributions to the engineering of semiconductor devices in 1977. He also awarded the IEEE Medal of Honor "for contributions to and leadership in tunneling, semiconductor superlattices, and quantum wells" in 1991 and the Japan Prize "for the creation and realization of the concept of man-made superlattice crystals which lead to generation of new materials with useful applications" in 1998.

## Esaki's "five don'ts" rules

In the 1994 Lindau Nobel Laureate Meetings, Esaki suggests a list of "five don'ts" which anyone in realizing his creative potential should follow. Two months later, the chairman of the Nobel Committee for Physics Carl Nordling incorporated the rules in his own speech.
* Don't allow yourself to be trapped by your past experiences.
* Don't allow yourself to become overly attached to any one authority in your field – the great professor, perhaps.
* Don't hold on to what you don't need.
* Don't avoid confrontation.
* Don't forget your spirit of childhood curiosity.

## Later years

Esaki moved back to Japan in 1992. Subsequently, he served as president of the University of Tsukuba and Shibaura Institute of Technology. Since 2006, he is the president of Yokohama College of Pharmacy. Esaki is also the recipient of The International Center in New York's Award of Excellence, the Order of Culture (1974) and the Grand Cordon of the Order of the Rising Sun (1998).
After the death of Yoichiro Nambu in 2015, Esaki is the eldest Japanese Nobel laureate.

## Recognition

In recognition of three Nobel laureates' contributions, the bronze statues of Shin'ichirō Tomonaga, Leo Esaki, and Makoto Kobayashi were set up in the Central Park of Azuma 2 in Tsukuba City in 2015.

### Awards and honors

List:
* 1959 – Nishina Memorial Prize
* 1960 – Asahi Prize
* 1961 – Stuart Ballantine Medal
* 1965 – Japan Academy Prize
* 1973 – Nobel Prize in Physics
* 1974 – Order of Culture
* 1985 – James C. McGroddy Prize for New Materials
* 1989 – Harold Pender Award
* 1991 – IEEE Medal of Honor
* 1998 – Japan Prize
* 1998 – Grand Cordon of the Order of the Rising Sun
* 2001 – Honorary Doctor at the Hong Kong University of Science and Technology
* 2007 – Honorary Distinguished Professor at the National Tsing Hua University

### Membership in learned societies

* 1960 Fellow of the American Physical Society
* Physical Society of Japan
* 1975 – Member, the Japan Academy
* 1976 – Foreign Associate, National Academy of Sciences
* 1977 – Foreign Associate, National Academy of Engineering
* 1989 – Member, Max Planck Society
* 1991 – Member, American Philosophical Society
* 1994 – Foreign Member, Russian Academy of Sciences
* 1995 – Honorary Foreign Member, Korean Academy of Science and Technology
* 1996 – Member, Accademia dei Lincei

## Family

Esaki's daughter, Anna Esaki, is married to Craig S. Smith, former Shanghai bureau chief of The New York Times and China bureau chief of The Wall Street Journal.