Investigation of terahertz emission phenomena of high-Tc, superconductors

The c-axis transmission spectra of underdoped Bi2Sr2CaCu2O8+delta (BSCCO) and YBa2Cu3O7-delta (YBCO) thin films were measured in the frequency range from 0.1 to 1.5 THz to investigate the mechanism of terahertz (THz)-pulse emission from high-T-C superconductors (HTSs). The transmission spectra showed different properties depending on both the kind and hole-doping level of HTS thin film. A relatively strong shielding effect was observed for THz waves below the characteristic frequency f(0), which almost corresponds to the cutoff frequency f(c) in the THz-wave radiation spectrum. The observed THz-pulse transmission and emission properties are explained by the intrinsic anisotropic characteristic peculiar to each HTS sample. Particularly, the magnitude of the superconducting order parameter that is induced in the insulating barrier layer between CuO2 double layers plays an important role in determining the cutoff frequency f(c).