  Nanorings asymmetrically connected to wires show different kinds of quantum
interference phenomena under sudden excitations and in steady current
conditions. Here we contrast the transient current caused by an abrupt bias to
the magnetic effects at constant current. A repulsive impurity can cause charge
build-up in one of the arms and reverse current spikes.
  Moreover, it can cause transitions from laminar current flow to vortices, and
also change the chirality of the vortex. The magnetic behavior of these devices
is also very peculiar. Those nano-circuits which consist of an odd number of
atoms behave in a fundamentally different manner compared to those which
consist of an even number of atoms. The circuits having an odd number of sites
connected to long enough symmetric wires are diamagnetic; they display
half-fluxon periodicity induced by many-body symmetry even in the absence of
electron-phonon and electron-electron interactions. In principle one can
operate a new kind of quantum interference device without superconductors.
Since there is no gap and no critical temperature, one predicts qualitatively
the same behavior at and above room temperature, although with a reduced
current. The circuits with even site numbers, on the other hand, are
paramagnetic.
