Esaki, Leo (1925-), a Japanese physicist, shared the 1973 Nobel Prize in physics for his discovery of an electronic phenomenon known as tunneling. His discovery led to the creation of a device known as the Esaki diode, or tunnel diode, which has practical applications in high-speed electronic circuits. The tunneling effect is widely used in the electronics industry.

Tunneling is a means by which electric current flows at a higher rate than predicted by what are known as classical theories of physics, which treat electrons as though they were particles. But according to quantum mechanics, electrons have characteristics of waves as well as particles.

Wave equations of quantum mechanics show how tunneling can occur.

Esaki was born on March 12, 1925, in Osaka, Japan. He earned his M.A. degree in physics at the University of Tokyo in 1947 and his Ph.D. degree in 1959. He worked as a researcher at Kobe Kogyo Corporation almost nine years, then joined Sony Corporation in Tokyo.

In 1957, Esaki noticed a tunneling effect in semiconductor junctions. A semiconductor is a material that conducts (carries) electric current better than an insulator like glass, but not as well as a conductor like copper. A semiconductor junction is a boundary between layers of a piece of semiconductor that have been altered in certain ways. Applying a voltage to a semiconductor junction can make an electric current flow across the junction. In tests conducted at Sony, an unusually high amount of current flowed across junctions when certain voltages were applied. Esaki determined that the size of the current was a tunneling effect.

Esaki shared the 1973 Nobel Prize in physics with British physicist Brian David Josephson and Norwegian-born American physicist Ivar Giaever .

Esaki came to the United States in 1960. At the IBM Thomas J. Watson Research Center, in Yorktown Heights, New York, he pioneered in the investigation of semiconductor superlattice. In 1993, he retired from IBM and became president of the University of Tsukuba in Japan.