Monolithic superconducting emitter of tunable circularly polarized terahertz radiation

We propose an approach to control the polarization of terahertz (THz) radiation from intrinsic Josephson-junction stacks in single crystalline high-temperature superconductor $Bi_2Sr_2CaCu_2O_{8+\delta}$. By monolithically controlling the surface current distributions in the truncated square mesa structure, we can modulate the polarization of the emitted THz wave as a result of two orthogonal fundamental modes excited inside the mesa. Highly polarized circular terahertz waves with a degree of circular polarization of more than 99% can be generated using an electrically controlled method. The emitted radiation has a high intensity and a low axial ratio (AR<1 dB). The intuitive results obtained from the numerical simulation based on the conventional antenna theory are consistent with the observed emission characteristics.Comment: Submitted to PRApplie

Polarization Enhancement of terahertz radiation generated by intrinsic Josephson junctions in a truncated edge square Bi_{2}Sr_{2}CaCu_{2}O_{8+{\delta}} mesa

In this study, we investigated the terahertz radiation from a truncated edge square mesa structure made from a superconducting Bi_{2}Sr_{2}CaCu_{2}O_{8+{\delta}} . Using a commercial software, the polarization characteristics were determined, and introduced, while accounting for the skin effect. The axial ratio was enhanced in the simulation by performing a parametric study on the design.Comment: Proceedings of the 28th International Symposium on Superconductivity, ISS 2015, November 16-18, 2015, Tokyo, Japa

Scaling behavior of the crossover to short-stack regimes of Josephson vortex lattices in Bi2_2Sr2_2CaCu2_2O8+δ_{8+\delta} stacks

We report the systematic investigations of the oscillation of the Josephson vortex (JV) flow resistance in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ micro-fabricated junctions with various geometries and superconducting anisotropy parameters. As the applied magnetic field parallel to the $ab$-plane is increased, oscillation with a period corresponding to a $\phi_0/2$ par atomic Josephson junction changes to oscillation with a doubled period. This crossover is scaled by both the junction length and the anisotropy parameter, indicating that the bulk inductive coupling that favors the triangular JV lattice is replaced with the surface deformation energy as the dominant interaction for a JV lattice. These results suggest that the in-phase square JV lattice is pronounced at a higher magnetic field in a smaller and more anisotropic sample.Comment: 4 pages, 3 figure