Cavity-mode excitation in a Josephson tunnel junction

Using Takanaka's theory of the zero-field dc-current steps of a Josephson tunnel junction, we have studied the effect of the junction $Q$ factor on the shape of the current step near the first even-order resonant voltage $V=h\frac{{\nu }_c}{e}$, where ${\nu }_c$ is the frequency of the fundamental cavity mode. In addition, we have found that the effect of a magnetic field on the step height can be qualitatively explained by modifying Takanaka's theory to include a magnetic-field-dependent term.