Lineshape of Josephson plasma resonance in underdoped Bi₂Sr₂CaCu₂O_8+δsingle crystals

Abstract

We have applied theoretical results derived by Koshelev and Bulaevskii, later refined by Coffey, to fit our experimental Josephson plasma resonance data for magnetic-field sweeps of underdoped Bi2Sr2CaCu2O8+δ single crystals with a Tc of approximately 72 K, measured in the frequency range between 19.2 and 31.6 GHz. Excellent fits were obtained for reduced temperatures of up to 0.55 in the case of the vortex liquid. We have also found that, for higher temperatures, the universal scaling function f(ζ) can be used to describe the obtained results with the fitting parameters Bb and Br. These fitting parameters change remarkably below the irreversibility line, which enables a distinction to be made between the pancake-gas and flux-line liquid states. In the case of the vortex solid, our fitting procedure was also working quite well.