Michael Tinkham

Rumford Research Professor of Physics; Gordon McKay Research Professor of Applied Physics

A.B., 1951, Physics and Mathematics, Ripon College
M.S., 1951, Ph.D., 1954, Physics, Massachusetts Institute of Technology



Metals in the superconducting state carry electrical current without resistance. These ``supercurrents'' are analogous to the current circulating within individual atoms of ordinary materials. Professor Tinkham and his group study the fundamental physics of superconducting phenomena and also their potentially important applications.

Much attention is currently directed toward small Josephson junctions, weak superconducting links between two strongly superconducting electrodes. Overlap tunnel junctions as small as 50 nm x 50 nm are fabricated in Gordon McKay Laboratory using facilities for photolithography, computer-controlled electron-beam lithography, thin-film deposition, and ion-beam etching. In junctions of such small capacitance (10^-15 F) the Coulomb charging energy e²/2C for a single electron is about 1K.

At lower (milliKelvin) temperatures, a small metallic island connected to leads through such tunnel junctions will usually contain exactly the number of electrons that minimizes the Coulomb energy. A finite voltage of order e/C must then be applied before a current will flow. In superconducting islands, the pairing and charging energies compete. With as many as 10⁹ electrons, states with even and odd numbers of conduction electrons can be distinguished. This property allows these devices to serve as photon-activated switches or ultrasensitive microwave detectors.

Devices in which the ``island'' is a metallic grain of ~10 nm dimension are now being studied. In grains this small, the energies of individual electronic states can be resolved by tunneling spectroscopy, permitting the study of many new phenomena.

Also under study are: (1) phase transitions in Josephson junction arrays with long-range interaction, and (2) electronic states and transport properties of carbon nanotubes and other quasi-one-dimensional systems.


See Also: Department of Physics