THz radiation properties of Tl2Ba2CaCu2O8+δ thin films excited by femtosecond laser pulses

Previously, we found the resonant THz wave radiation from c-axis oriented underdoped Tl₂Ba₂CaCu₂O_8+δ (Tl-2212) thin films by femtosecond laser pulse illumination under magnetic field. The properties of the resonant THz wave were well explained by the Josephson plasma resonance phenomenon. In the present study, the THz radiation properties were investigated for an overdoped Tl-2212 thin films. The amplitudes of THz waveform radiated under a bias current condition is much smaller than those of previous sample, while any trace of resonant THz signals could not be observed under magnetic field. These experimental results indicate the possibility that the initial THz wave radiated by ultrafast modulation in eddy-current around the vortices has an important role to excite the collective mode oscillation.