The superconductor-insulator transition exhibits a remarkable duality symmetry directly relating the resistance measured in the superconducting regime to the conductance measured in the insulator. This symmetry points to a deep relation between these two seemingly-opposing phases. At very low temperatures (below 200 mK for our amorphous indium-oxide films) this beautiful symmetry is severely violated. We demonstrate that this violation is associated with the emergence of a new insulating ground-state in which the electrons are effectively decoupled from the host phonons. We further show that duality symmetry can be effectively restored by driving the system out of equilibrium.
 D.M. Basko, I.L. Aleiner, B.L. Altshuler, Annals of Physics 321, 1126 (2006); D.M. Basko, I.L. Aleiner, B.L. Altshuler, Phys. Rev. B 76, 052203 (2007)