Instanton Aharonov-Bohm effect and macroscopic quantum coherence in charge-density-wave systems

It is predicted that in a charge-density-wave (CDW) ring-shaped conductor, placed in an external vector-potential field, there should appear a new Aharonov-Bohm contribution to the magnetic susceptibility and the electrical conductivity oscillating as a function of the flux with the period ${\mathrm{\Phi }}_0$=hc/2e. This contribution arises from instanton transitions between degenerate vacua of the CDW condensate and is the solid-state realization of Θ vacuum in quantum field theory. The period transforms into ${\mathrm{\Phi }}_0$/N in N strongly correlated parallel CDW chains.