Nonresonant microwave absorption in Bi2212 single crystal: Second peak and microwave power dependence

Nonresonant microwave absorption (NMA) measurements were carried out at liquid-nitrogen temperature on a high quality Bi2212 single crystal, as a function of microwave power in three mutual orientations of crystal nb plane, de field (H-dc) and microwave magnetic field (H-w). NMA line shapes in Bi2212 crystal are complicated with a narrow peak (PI peak) located near zero field, followed by a much broader second peak (P-2 peak) in the particular orientations. More excitingly, we show that the P-2 peak qualitatively evolves as a function of microwave power in the orientation of H-dc perpendicular to ab plane, H-w // ab plane, and H-dc perpendicular to H-w. In this configuration, as the microwave power is progressively increased, the broad Pt peak first gets smeared off and then a multiple peak structure appears, which develops into another narrower second peak (P-s-peak) at high enough microwave powers. In the orientation of H-dc // ab plane, H-w perpendicular to ab plane, and H-dc perpendicular to H-w, we report for the first time the: appearance and disappearance of a new second peak (P-2-like peak) as a function of microwave power.