Number 58 (Story #1), December 5, 1991 by Phillip F. Schewe and Ben Stein|
PERSISTENT CURRENTS , currents that do not decay, have long been known to exist in superconductors. In 1990 scientists at AT&T Bell Labs showed that persistent currents could also exist in normal metal rings of sufficiently small size, verifying a prediction made in 1983. In particular they measured the magnetization of an ensemble of 107 copper rings, each only 0.5 microns in diameter. Now a group at the IBM Watson Research Center has measured the magnetic response of single, isolated (micron-sized) gold loops (V. Chandrasekhar et al., Physical Review Letters, 16 December 1991). The current in the loops was found to oscillate with a period proportional to the magnetic flux threading the loops, as expected, but the size of the current was larger than expected by a factor of from one to two orders of magnitude.