Dynamic response of microwave absorption triggered by magnetic modulation in high anisotropy Bi 2Sr 2CaCu 2O x crystals

Abstract

We study magnetic field modulated microwave absorption in Bi 2Sr 2CaCu 2O x single crystals. In addition to the well-known signal corresponding to the field derivative of the thermally-activated flux-flow resistivity, which appears close to T c and depends linearly on the modulation level, we observe a new signal with a nonlinear (NL) dependence on the magnitude of the modulation field. This new signal (i) extends to low temperatures, (ii) appears only above some threshold modulation level, (iii) strongly depends on the magnitude and direction of the d.c. magnetic field, and (iv) appears only in highly anisotropic superconductors. It cannot be simulated from the microwave dissipation measurements of Enriquez et al. where an almost identical experimental set up was used but without magnetic field modulation. Hence, the NL signal is due to dynamic response triggered by the magnetic modulation. We suggest that the NL signal arises from the removal of vortices out of their shallow pinning potential well by the modulation magnetic field.