  The observation of the Kondo effect in mesoscopic systems under bias$^{1,2}$
has opened a new chapter in the physics of the Kondo phenomenon. Various types
of $dI/dV$, where $I$ and $V$ denote current and source-drain (s-d) bias,
respectively, line shapes have been measured by scanning tunneling microscopy
(STM)$^{1,3-11}$. However, explanation by single Fano line shape$^{1,12-16}$ is
not relevant and even misleading. Here, we provide consistent explanations for
various asymmetric and symmetric line shapes in terms of a microscopic theory
that shows the creation of two resonant tunneling levels (RTLs) when bias is
applied$^{17}$. One side Kondo coupling between adatom and substrate does not
create Kondo peak that appears only when the system has an overall Kondo
coupling including both substrate and tip. The structure of an asymmetric line
shape is mostly governed by the RTL peaks. Therefore, Kondo effect is
negligible in most asymmetric line shapes.
