Science:
Why do some solids conduct electricity like a metal, and others
act like insulators? Quantum mechanics has provided some
relatively simple (and quite successful) models for electron
conductivity, but the underlying physics is often complex,
because electrons interact with each other through Coulomb
forces and because real materials are not perfectly ordered.
In
the December 5 issue of Science, Schneider et al. address
the microscopic distinction between a conductor and an
insulator by examining the conducting properties of repulsively
interacting 40K atoms, which, like electrons, are
fermions--they have half-integer spin and obey the Pauli
Exclusion Principle, which allows only one fermion to occupy a
quantum state. By placing ultracold 40K atoms in an artificial
crystal held in place through optical fields, they can
manipulate the energy scales of the system so that it varies
all the way from a metallic state to different kinds of
insulating phases.
