  Lower thermal stability due to thinning often leads to unprecedented hidden
phases in low-dimensional materials. Such hidden phases can coexist or compete
with preexisting electronic phases. We investigate hidden phases observed in
atomically thin (6-8 layers) 1T-TaS$_2$ with scanning tunneling microscopy.
First, we can electrically induce a hidden stripe phase at room temperature.
Such a uniaxial stripe phase has three equivalent orientations by breaking
three-fold symmetry of 1T-TaS$_2$. We also reveal that the hidden stripe phase
coexists with nearly commensurate charge-density-wave phase. Next, we observe
that the emergent stripe phase spontaneously appears without any electric
excitation on a tiny flake ($160\times80$ nm$^2$). Our findings may provide a
plausible explanation for the previously observed phase transition and two-fold
optical response in thin 1T-TaS$_2$ devices at room temperature. Furthermore,
the hidden stripe phase would be crucial to understand exotic CDW-related
phenomena in 1T-TaS$_2$ for potential applications.
