Esaki, Leo (1925– )

Japanese physicist who in 1957 noticed that electrons could sometimes ‘tunnel’ through the barrier formed at the junctions of certain semiconductors. The effect is now widely used in the electronics industry.

Esaki was awarded the Nobel Prize for Physics in 1973 for this early discovery of the tunnelling phenomenon in semiconductors and superconductors. He shared the award with British physicist Brian Josephson and Norwegian-born US physicist Ivar Giaever.

Esaki, born in Osaka, graduated from the University of Tokyo and worked for electronics manufacturer Sony 1956–60. He then joined IBM's research centre in Yorktown Heights, New York, but returned to Japan 1992 as president of the University of Tsukuba.

Tunnelling is a quantum-mechanical effect whereby electrons can travel through electrostatic potentials that they would be unable to overcome classically. Esaki was able to use this effect for switching and to build ultrasmall and ultrafast tunnel diodes, now called Esaki diodes. He continued to research the nonlinear transport and optical properties of semiconductors, in particular multilayer superlattice structures grown by molecular-beam epitaxy techniques.