Collective dynamics of macroscopic quantum tunnelling in layered high-Tc superconductors

In order to construct a theory for photon-assisted macroscopic quantum tunnelling (MQT) in intrinsic Josephson junctions, we revisit the model of capacitively coupled intrinsic Josephson junctions and clarify how the quantized energy levels in the N-junction stacked system distribute inside a valley of the Josephson sinusoidal potential. Furthermore, we reveal that the MQT escape rate from the single-plasmon states to the uniform voltage ones by microwave irradiation is proportional to the square of the junction number (N²) in multi-photon processes. This result is consistent with the recent finding in Bi-2212 intrinsic Josephson junctions by Jin et al 2006 Phys.Rev.Lett.96177003.