  Current searches for the light top squark (stop) mostly focus on the decay
channels of $\tilde{t} \rightarrow t \chi_1^0$ or $\tilde{t} \rightarrow b
\chi_1^\pm \rightarrow bW \chi_1^0$, leading to $t\bar{t}/bbWW+\met$ final
states for stop pair productions at the LHC. However, in supersymmetric
scenarios with light neutralinos and charginos other than the neutralino
lightest supersymmetric particle (LSP), more than one decay mode of the stop
could be dominant. While those new decay modes could significantly weaken the
current stop search limits at the LHC, they also offer alternative discovery
channels for stop searches. In this paper, we studied the scenario with light
Higgsino next-to-LSPs (NLSPs) and Bino LSP. The light stop decays primarily via
$\tilde t_1 \to t \chi_2^0/\chi_3^0$, with the neutralinos subsequent decaying
to a $Z$ boson or a Higgs boson: $\chi_2^0/\chi^0_3 \to \chi_1^0 h/Z$. Pair
production of light stops at the LHC leads to final states of $t \bar t
hh\met$, $t \bar t hZ\met$ or $t \bar t ZZ\met$. We consider three signal
regions: one charged lepton (1$\ell$), two opposite sign charged leptons (2 OS
$\ell$) and at least three charged leptons ($ \ge 3 \ell$). We found that the
1$\ell$ signal region of channel $t \bar t hZ\met$ has the best reach
sensitivity for light stop searches. For 14 TeV LHC with 300 ${\rm fb}^{-1}$
integrated luminosity, a stop mass up to 900 GeV can be discovered at 5$\sigma$
significance, or up to 1050 GeV can be excluded at 95\% C.L. Combining all
three decay channels for $1 \ell$ signal region extends the reach for about
100$-$150 GeV. We also studied the stop reach at the 100 TeV $pp$ collider with
3 ${\rm ab}^{-1}$ luminosity, with discovery and exclusion reach being 6 TeV
and 7 TeV, respectively.
