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Esaki, Leo

Leo Esaki

Leo Esaki (born 1925) was one of three winners of the Nobel Prize in Physics in 1973. Esaki was honored for his 1957 pioneering work in electron tunneling in semiconducting materials, which led to his creation of the Esaki diode, or tunnel diode. This technology helped advance research in optical and wireless communication devices. Esaki left Japan in 1960 to conduct research on semiconductor superlattice structures at IBM in the United States, a country more open to scientific research than Japan. He returned to his home country in 1992 to serve as president of Tsukuba University where he encour aged collaborative research between graduate students and industrial research labs.

Turned His Attention to Physics

Reiona "Leo" Esaki was born in Osaka, Japan, the son of Soichiro, an architect, and Niyoko. He attended Third High School, similar to a junior college, in Kyoto. Interestingly, this school produced all three of Japan's Nobel Prize winners in Physics, a testament to its development of scientific talent. Esaki then attended the University of Tokyo, majoring in physics, and earning his MS degree in 1947.

World War II and an interest in understanding how the world works made Esaki first want to do research in nuclear physics. However, Japan, which was rebuilding after the war, did not have the equipment necessary to conduct tests in this field. With a desire to participate in his country's rebuilding, Esaki switched to industrial research and the field of solid-state physics, or the study of semiconductors, which was gaining attention from the accomplishments of pioneer William Shockley.

After he graduated, Esaki joined Kobe Kogyo Corporation as a researcher and stayed for nearly nine years. In 1956, he became chief physicist at Tokyo Tsushin Kogyo, a forerunner of what is today Sony Corporation, serving for four years. At the same time he worked toward his Ph.D. thesis at Tokyo University.

Discovered Tunnel Diode

As part of a small research group at Sony in 1957, Esaki experimented with semiconductor materials and invented what is called the Esaki tunnel diode. By studying p-n junctions, or barriers, made of heavily doped (meaning they have high impurity levels) germanium (Ge) and silicon (Si), Esaki discovered that electric current could be made to cross those junctions. When he applied a voltage to a semiconductor junction, electrons in the current jumped over the junction, resulting in a quantum mechanical "tunneling" effect. He was surprised to learn that the electrons' resistance to the barrier decreased with the intensity of the voltage, the opposite of what was expected.

This tunnel diode allowed electrons to pass through junctions that were only a hundred atoms thick. Tunneling was possible using wave equations of quantum mechanics, rather than approaching the phenomenon using classical theories of physics, in which electrons are thought of as particles.

Esaki published his findings in 1958, answering questions about electron tunneling through solids that scientists had been asking for decades, and opening a new field in development of solid-state physics that spread to research laboratories around the world. The knowledge of tunneling in semiconductors was useful in practical applications, as super-fast and super-small electrons that could cross barriers would be useful for high-speed circuits. Esaki used his discovery and research for his graduate thesis which earned him a Ph.D. in Physics from Tokyo University in 1959.

The profound impact of the Esaki tunnel diode, in not only his scientific achievement but in creating a basis for other researchers to study, was recognized by a string of accolades. He received Japan's Nishina Memorial Award in 1959; the Asahi Press Award in 1960; the Morris N. Liebmann Memorial Prize from IRE, the Stuart Ballantine Medal from the Franklin Institute, and the Toyo Rayon Foundation Award, all in 1961; the Japan Academy Award in 1965; and the Order of Culture from the Japanese government in 1974.

Joined IBM in United States

In 1960, Esaki was invited to work as a resident consultant at International Business Machines (IBM) in Yorktown, New York, in the United States. His one-year visit soon extended to a 32-year stay after IBM awarded him a fellowship to continue his research in semiconductor physics at the IBM Thomas J. Watson Research Center.

Esaki's departure from Sony was surprising to many. In Japan, companies were known for giving employees lifetime employment; people seldom changed jobs. Now, a highly regarded scientist was leaving his country to work in the United States, where it was known that scientific research and curiosity were more highly valued. So unprecedented was Esaki's move, that both Sony and IBM released press announcements saying that he was leaving under honorable circumstances.

During his years at the Watson center, Esaki investigated man-made semiconductor superlattice structures to predict quantum mechanical phenomena. He and Raphael Bu published papers in 1969 and 1970 that proposed that single-crystal superlattice structures with unusual electronic properties could be designed using quantum theory and advanced techniques of epitaxy. These lattices are composed of layered thin films which can carry current at discrete voltages. In 1972, Esaki discovered a negative differential conductivity in GaAIAs (gallium aluminum arsenide) superlattice. He confirmed through experimentation, a year later, a resonant tunneling phenomenon between adjacent potential quantum wells in the superlattice structure.

A successful member of IBM, Esaki became director of IBM-Japan in 1976 serving until 1992, and was named to the governing board of the IBM-Tokyo Research Laboratory.

Awarded Nobel Prize in Physics

Esaki was awarded the Nobel Prize in Physics in 1973 for his pioneering work in electron tunneling in semiconducting materials, which led to his creation of the tunnel diode. He shared the award that year with British physicist Brian David Josephson and Norwegian-born American physicist Ivar Giaever.

This technology has been at the core of further research in semiconductor science. In the area of semiconductor lasers, this technology has applications such as optical telecommunications, wireless communication devices, and data readers in computer hard disks. Other applications and research involve nonlinear transport and optical properties on semiconductors, junctions, and thin films.

Esaki's notoriety in his field continued to grow with more scientific recognition. He received the US-Asia Institute Science Achievement Award in 1983. In 1985, he and two others shared the American Physical Society's International Prize for New Materials for pioneering the study of semiconductor quantum structures. The Institute of Electrical and Electronic Engineers awarded him the Medal of Honor for 1991 for his scientific contributions in tunneling, superlattices, and quantum wells.

Over the course of two decades, Esaki joined an impressive number of professional associations and sat on company boards. He served on the board of Yamada Science Foundation, as a member of the Japan Academy, and was adjunct professor of Waseda University in Japan. He was elected a fellow of the American Academy of Arts and Sciences in 1974, and named a foreign associate of both the US National Academy of Sciences in 1976 and US National Academy of Engineering in 1977.

Many international organizations named Esaki as a foreign member, including the Russian Academy of Sciences, Korean Academy of Science and Technology, Italian National Academy of Science, Max-Planck Gesellschaft, and American Philosophical Society. Esaki was named a Sir John Cass Sr. Visiting Research Fellow at London Polytechnic in 1981.

Named President of Tsukuba University in

In 1992, Esaki retired from IBM and returned to Japan, where he had retained his citizenship. He accepted a position as president of Tsukuba University in Ibaraki, Japan. His selection for president was an unusual one, as he had been living away from Japan for the past thirty years, and had become the first person outside of academia to lead a national university in Japan.

Tsukuba University held an attraction for Esaki for two reasons. Founded in 1973, the year he won the Nobel Prize, the school had been built near Tsukuba Science City, Japan's first government planned high-tech community. Secondly, the school promised to change the stifling Japanese method of learning by rote and suppressing creativity by encouraging original thought and interactions between students and research labs. After nearly two decades, the school had yet to achieve those lofty goals. Several young professors called Esaki to help lead their school in the direction toward scientific research. Esaki noted, "Revitalizing creative activity at University of Tsukuba is the main reason I was invited to become president."

Esaki originally left Japan due to the country's paradoxical approach to science. Despite students garnering traditionally high marks in science, compared to other industrialized countries, Japan placed little emphasis in technological development. That's why the country has produced only five Nobel science and medicine laureates, compared to America's 191. Esaki noted that, "Not many people in Japan appreciated the tunnel diode when I made it in 1957. There was not much commercial application. But the US science community really appreciated it. That is why I went to America first of all and that is why I stayed there." Esaki made his mission at Tsukuba University to create the supportive environment for scientists in Japan that he had craved as a young man.

The transition to Esaki's presidency was not a smooth one. Faculty is traditionally promoted through seniority and elected from within. Esaki was considered an outsider. He told Science magazine, "This is almost a 'forbidden transition,' going from industry to academia—especially in Japan." Another concern was that he had become too Americanized and would have a difficult time fitting back into Japanese business. But he had been traveling back to Japan from the US several times a year and keeping close ties to his homeland. Esaki used his experience at IBM to help adjust. "I know how to manage the bureaucracy and politicians," he said.

Urged Research Collaborations for Graduate Students

During his four-year term at Tsukuba University, his goal was to transform the school into a first-rate research institution by encouraging collaborations and scientist exchanges between the school and Tsukuba City's corporate labs and government institutes. He also had to contend with the Japanese government's meager contribution to applied research, which lagged far behind the Research & Development funding of the US. To achieve his goal, he built industry/university relations by establishing the Tsukuba Advanced Research Alliance (TARA) to encourage collaborative Research & Development between private research institutes, Tsukuba University, and national government labs.

Dear to his heart was the desire to expand and strengthen the school's graduate education. Since one quarter of the university's population was graduate students, Esaki created a program that allowed doctoral candidates to work in participating industrial or government labs around Tsukuba Science City. He also negotiated educational exchange programs with universities in the US and Europe. These benefits did not extend strictly to science majors, but also for humanities and social sciences. Other changes he recommended included more interdisciplinary focus, increased use of outside peer review, greater diversity of faculty and students, and increased spending on facilities.

Became President of Shibaura Institute of Technology

In 1998, Esaki received the Japan Prize in the category of "Generation and Design of New Materials Creating Novel Functions" for the creation of the concept of man-made superlattice crystals which lead to new materials with useful applications. The prize came with an award of 50 million yen, about $391,000. That same year, he received the Grand Cordon Order of Rising Sun (First Class), and was named chairman of the Science and Technology Promotion Foundation of Ibaraki, Japan. In 1999, he was named director general of Tsukuba Institute Congress Center.

In 2000, Esaki became president of Shibaura Institute of Technology where he concentrated on the upgrading and internationalization of Japan's education system and academic research program. He also served as director of Open Loop, Inc., a Sapporo-based firm that develops security technology.

Over the years, Esaki earned honorary degrees from schools across the globe, including University of Montpellier in France, University of Athens in Greece, and Universidad Politecnica de Madrid in Spain. Esaki published numerous papers in professional journals and served a time as guest editorial writer for Yomiuri Press. Through clever articles he has helped create a bridge of understanding between Japan and the West. Esaki is married with three children.


Asimov's Biographical Encyclopedia of Science and Technology, Doubleday and Company, 1982.

McGraw Hill's Modern Scientists and Engineers, McGraw Hill, 1980.

World Book Biographical Encyclopedia of Scientists, World Book, 2003.


Physics Today, October 1992.

Science, December 1994; January 9, 1998.

U.S. News & World Report, June 9, 1997.


Institute of Electrical and Electronic Engineers History Center, (December 23, 2003).

Japan Prize, (December 12, 2003).

Nobel Museum, (December 12, 2003).

World of Scientific Discovery, 2nd ed. Gale Group, 1999.

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Esaki, Leo

Esaki, Leo (1925– ) Japanese physicist, who developed the tunnel diode, a semiconductor that allows electrons to cross normally impassable electronic barriers. US physicist Ivar Giaever extended Esaki's research to the field of superconductivity. For this work, they shared the 1973 Nobel Prize in physics with Brian Josephson. The Esaki diode is used in computer data storage.

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