Relaxation study of elementary excitations in Bi2212 investigated by picosecond Raman spectroscopy

We report a relaxation study of elementary excitations in heavily underdoped Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212) using picosecond Raman Spectroscopy. In B 1 g symmetry, the two‐magnon peak shows a super‐linear power dependence which is ascribed to excess magnon population. In contrast, the broad feature observed in A 1 g + B 2 g symmetry shows a sub‐linear power dependence, suggesting a different origin from the two‐magnon scattering. We could recognize a time response <0.5 ps for the B 1 g two‐magnon peak. We also observed super‐linear behavior in the power dependence of the 295 and 465 cm −1 anti‐Stokes vibrational modes, in contrast to linear behavior on the Stokes side. We propose to explain the non‐linear behavior in terms of non‐equilibrium phonons. Copyright © 2002 John Wiley & Sons, Ltd.