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 ab plane, dc field (H_dc), and microwave magnetic field (H_w). NMA line shapes in Bi2212 crystal are complicated with a narrow peak (P₁ peak) located near zero field, followed by a much broader second peak (P₂ peak) in the particular orientations. More excitingly, we show that the P₂ peak qualitatively evolves as a function of microwave power in the orientation of H_dc ab plane, plane, and H_dc H_w. In this configuration, as the microwave power is progressively increased, the broad P₂ 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 plane, H_w ab plane, and H_dc H_w, we report for the first time the appearance and disappearance of a new second peak (P₂-like peak) as a function of microwave power.