  Shrinking the size of a bulk metal into nanoscale leads to the discreteness
of electronic energy levels, the so-called Kubo gap. Renormalization of the
electronic properties with a tunable and size-dependent Kubo gap renders
fascinating photon emission and electron tunneling. In contrast with usual
three-dimensional (3D) metal clusters, here we demonstrate that Kubo gap can be
achieved with a two-dimensional (2D) metallic transition metal dichalcogenide
(i.e., 1T'-phase MoTe2) nanocluster embedded in a semiconducting polymorph
(i.e., 1H-phase MoTe2). Such a 1T'-1H MoTe2 nanodomain resembles a 3D metallic
droplet squeezed in a 2D space which shows a strong polarization catastrophe
while simultaneously maintains its bond integrity which is absent in
traditional delta-gapped 3D clusters. The weak screening of the host 2D MoTe2
leads to photon emission of such pseudo-metallic systems and a ballistic
injection of carriers in the 1T'-1H-1T' homojunctions which may find
applications in sensors and 2D reconfigurable devices.
