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[1]. We further show that duality symmetry can be effectively restored by driving the system out of equilibrium.
[1] 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)