Surface effects in THz wave emission from intrinsic Josephson junctions

Recently THz wave emission from intrinsic Josephson junctions without external fields [1] was observed experimentally. As possible states to characterize this emission, the McCumber-like state with little spatial dependence of electric fields (for the surface impedance $Z=1$) [2] and novel phase-kink state (for large and complex $Z$) [3] have been proposed. In the present study [4] it is numerically shown that both states are stationary and that the dynamical phase transition between these two states occurs as $Z$ is varied. The McCumber-like state is stable for low current and small $Z$. For higher current, the phase-kink state accompanied with symmetry breaking along the $c$ axis is stable even for $Z=1$, though strong emission in the vicinity of cavity resonance points only takes place for larger $Z$. Value of $Z$ is optimized for the strongest emission, and effect of surface roughness will also be discussed. [1] L.~Ozyuzer {\it et al.}, Science {\bf 318}, 1291 (2007); K. Kadowaki {\it et al.}, Physica C {\bf 468}, 634 (2008). [2] H.~Matsumoto {\it et al.}, Physica C {\bf 468}, 654, 1899 (2008). [3] S.~Lin and X.~Hu, Phys.\ Rev.\ Lett.\ {\bf 100}, 247006 (2008). [4] Y.~Nonomura, arXiv:0810.3756.