Second-Order Josephson Effect in Excitonic Insulators

We show that in electron-hole bilayers with excitonic orders arising from conduction and valence bands formed by atomic orbitals that have different parities, nonzero interlayer tunneling leads to a second-order Josephson effect. This means the interlayer electrical current is related to the phase of the excitonic order parameter as J={J}_{c}\mathrm{sin}2\ensuremath{\theta}instead of J={J}_{c}\mathrm{sin}\ensuremath{\theta}and that the...