Squeezed metallic droplet with tunable Kubo gap and charge injection in transition metal dichalcogenides

Significance We propose an approach to realize Kubo gap in 2D nanodomains, which mimics three-dimensional (3D) metallic droplets squeezed into atomically thin 2D space. We demonstrate 1H/1T′ phase transition of the MoTe2 nanodomain driven by strain and excess carriers, and a strong anisotropy for a ballistic injection of carriers. Breaking away from traditional trend of focusing almost exclusively on 3D metal clusters for producing Kubo gap, our work reveals the possibility of Kubo gap production in 2D systems like MoTe2. By overcoming the intrinsic limitations of the former, this approach can bring about potential technical possibilities, as well as new scientific activities related to the Kubo-gapped systems, such as efficient quantum emitters and catalysis, and reconfigurable devices. Shrinking the size of a bulk metal into nanoscale leads to the discreteness of electronic energy levels, the so-called Kubo gap δ. Renormalization of the electronic properties with a tunable and size-dependent δ renders fascinating photon emission and electron tunneling. In contrast with usual three-dimensional (3D) metal clusters, here we demonstrate that Kubo gap δ 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 maintaining its bond integrity, which is absent in traditional δ-gapped 3D clusters. The weak screening of the host 2D MoTe2 leads to photon emission of such pseudometallic systems and a ballistic injection of carriers in the 1T′/1H/1T′ homojunctions which may find applications in sensors and 2D reconfigurable devices.