  The discovery of high-mobility two-dimensional electron gas and low carrier
density superconductivity in multiple SrTiO$_3$-based heterostructures has
stimulated intense interest in the surface properties of SrTiO$_3$. The recent
discovery of high-T$_c$ superconductivity in the monolayer FeSe/SrTiO$_3$
aroused the upsurge and underscored the atomic precision probe of the surface
structure. By performing atomically resolved cryogenic scanning tunneling
microscopy/spectroscopy characterization on
dual-TiO$_{2}$-${\delta}$-terminated SrTiO$_3$(001) surfaces with ($\sqrt{13}$
$\times$ $\sqrt{13}$), c(4 $\times$ 2), mixed (2 $\times$ 1), and (2 $\times$
2) reconstructions, we disclosed universally broken rotational symmetry and
contrasting bias- and temperature-dependent electronic states for apical and
equatorial oxygen sites. With the sequentially evolved surface reconstructions
and simultaneously increasing equatorial oxygen vacancies, the surface
anisotropy reduces, and the work function lowers. Intriguingly, unidirectional
stripe orders appear on the c(4 $\times$ 2) surface, whereas local (4 $\times$
4) order emerges and eventually forms long-range unidirectional c(4 $\times$ 4)
charge order on the (2 $\times$ 2) surface. This work reveals robust
unidirectional charge orders induced by oxygen vacancies due to strong and
delicate electronic-lattice interaction under broken rotational symmetry,
providing insights into understanding the complex behaviors in perovskite
oxide-based heterostructures.
