1. b Bell Laboratories , Murray Hill , New Jersey , 07974 , U.S.A.
2. a Department of Physics and Center for Materials Science and Engineering , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , U.S.A
3. c Hewlett Packard, Andover Div. , 1776 Minuteman Road, Andover , Massachusetts , 01810 , U.S.A.