  Interlayer coupling is strongly implicated in the complex electronic
properties of 1$T$-TaS$_2$ , but the interplay between this and electronic
correlations remains unresolved. Here, we employ angle-resolved photoemission
spectroscopy (ARPES) to reveal the effect of uniaxial strain engineering on the
electronic structure and interlayer coupling in 1$T$-TaS$_2$ . The normally
insulating ground state is transformed into a correlated-metal phase under
strain, as evidenced by the emergence of a narrow band at the Fermi level.
Temperature dependent ARPES measurements reveal that the metallic behaviour
only develops below the commensurate charge density wave (CCDW) transition,
where interlayer dimerization produces a band-insulator in unstrained samples.
Electronic structure calculations demonstrate that the correlated metallic
behaviour is stabilized by a previously predicted but unobserved bulk stacking
structure with a modified interlayer coupling of the Ta d$_{z^{2}}$ electrons.
Our combined approach lays bare the role of correlations and interlayer
coupling in 1$T$-TaS$_2$ , providing critical input for understanding
superconductivity under pressure and the metastable hidden phase induced using
non-equilibrium protocols in this platform material for correlated physics.
