  Artificially created two-dimensional (2D) interfaces or structures are ideal
for seeking exotic phase transitions due to their highly tunable carrier
density and interfacially enhanced many-body interactions. Here, we report the
discovery of a metal-insulator transition (MIT) and an emergent gapped phase in
the metal-semiconductor interface that is created in 2H-MoTe$_2$ via
alkali-metal deposition. Using angle-resolved photoemission spectroscopy, we
found that the electron-phonon coupling is strong at the interface as
characterized by a clear observation of replica shake-off bands. Such strong
electron-phonon coupling interplays with disorder scattering, leading to an
Anderson localization of polarons which could explain the MIT. The domelike
emergent gapped phase could then be attributed to a polaron extended state or
phonon-mediated superconductivity. Our results demonstrate the capability of
alkali-metal deposition as an effective method to enhance the many-body
interactions in 2D semiconductors. The surface-doped 2H-MoTe$_2$ is a promising
candidate for realizing polaronic insulator and high-$T_c$ superconductivity.
