Nonlinear microwave response to magnetic modulation in BSCCO

We study magnetic field modulated microwave absorption in BiSrCaCuO single crystals, In addition to the well-known signal corresponding to the field-d erivative of the thermally activated flux-flow resistivity, which appears c lose to T-c and linearly depends on the modulation level, we observe a new signal with a nonlinear dependence on the modulation field. This new signal (i) extends to low temperatures, (ii) appears only above some threshold mo dulation level, (iii) strongly depends on the magnitude and direction of th e de magnetic field, (iv) appears only in highly anisotropic superconductor s. (C) 2000 Published by Elsevier Science B.V. All rights reserved.