Spin polarized tunneling in large area mesas of superconducting Bi2Sr2CaCu2O8+δ for the generation of the THz waves

Rectangular intrinsic Josephson junction mesa structures of superconducting Bi₂Sr₂CaCu₂O_8+Δ (Bi2212) can be used as a source of continuous, coherent and polarized terahertz (THz) radiation. THz emitting mesas are below a certain underdoped level of Bi2212. They have small Josephson critical current in contrast to optimally doped and overdoped Bi2212. We deposited Au/Co/Au multilayer top of mesa and obtained small critical current from mesas fabricated by as-grown Bi2212 single crystals due to injection of spin polarized current. The spin injection eliminates adjustment of doping level for successful THz emission.