  Superconductivity (SC) in twisted bilayer graphene (tBLG) has been explored
by varying carrier concentrations, twist angles, and screening strength, with
the aim of uncovering its origin and possible connections to strong electronic
correlations in narrow bands and various resulting broken symmetries. However,
the link between the tBLG band structure and the onset of SC and other orders
largely remains unclear. In this study, we address this crucial gap by
examining in-situ band structure tuning of a near magic-angle ($\theta
\approx0.95^0$) tBLG device with displacement field ($D$) and reveal remarkable
competition between SC and other broken symmetries. At zero $D$, the device
exhibits superconducting signatures without the resistance peak at
half-filling, a characteristic signature with a strong electronic correlation.
As $D$ increases, the SC is suppressed, accompanied by the appearance of a
resistance peak at half-filling. Hall density measurements reveal that at zero
$D$, SC arises around the van Hove singularity (vHs) from an isospin or
spin-valley unpolarized band. At higher $D$, the suppression of SC coincides
with broken isospin symmetry near half-filling with lifted degeneracy ($g_d
\sim 2$). Additionally, when SC is suppressed at higher $D$, density waves
around the superconducting dome are seen. These findings, with our theoretical
calculations, highlight the competition between SC and other orders, and the
stabilization of the latter by the electric field enhanced nesting in the band
structure of tBLG.
