We argue the coherent part of the spectral weight always contribute symmetrically to the STM spectrum at sufficiently low energy and the tunneling asymmetry is a manifestation of the incoherent part of the electron spectrum. By subtracting the particle side spectrum from the hole side spectrum in the published STM data of Pan \textit{ et al} on $BSCCO_{ 2212}(T_{ c}=84K)$, we find the difference spectrum show a well defined gap structure at 25 meV. We argue this gap may represent a new energy scale of the system, namely the energy scale for spin-charge recombination in this system.
Categories: cond-mat.supr-con cond-mat.str-el