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                                PHYSICS
                              COLLOQUIUM
                         UNIVERSITY OF TORONTO

		      Thursday, January 14, 1993
			 4:10 p.m.  Room 102
		    McLennan Physical Laboratories
                        60 St. George Street

Speaker                    DR. MARIE D'IORIO
                   National Research Council Canada
                Institute for Microstructural Sciences

Topic              "TWO-DIMENSIONAL ELECTRON SOLID:
           FROM WIGNER'S PREDICTIONS TO CURRENT EXPERIMENTS"

      Fifty years ago Wigner predicted that conduction electrons, if
sufficiently dilute, should condense from their normal extended states
to an electron solid now known as the "Wigner crystal".  It was
realized much later that the correlation energy makes Wigner
crystallization in two dimensions (2D) more favorable, e.g. at a
semiconductor interface or on the surface of liquid helium.  The helium
system was the first to show 2D electron crystallization but forms a
classical electron crystal rather than Wigner's quantum one.
Semiconductor interfaces prepared by molecular epitaxy can have a
dilute concentration of electrons confined in 2D with remarkably few
defects that might localize the electrons.  Using the best Si/SiO2
samples (from Russia), we have probed the transport of electrons and
found spectacular transitions from the metallic to the insulating
state.  The experimental evidence gathered at NRC points to the
formation of a quantum zero-field electron solid- the "true" Wigner
crystal.  A review of the basic concepts and definitive experiments
will be given.