Ultrafast Interfacial Carrier Dynamics and Persistent Topological Surface States in VSe2/Bi2Se3 Van Der Waals Heterojunctions

Abstract Vanadium diselenide (VSe2) has recently been highlighted as an efficient 2D electrode owing to its extra-high conductivity, thickness-controllability, and van der Waals epitaxial contact. However, as the electrode, applications of VSe2 to various material systems are still lacking. Here, by employing ultrafast time-resolved spectroscopy, we study VSe2-thickness-dependent interfacial effects in heterostructures with topological insulator Bi2Se3 that is severely affected by contact with conventional 3D electrodes. Our results particularily show unaltered Dirac surface state of Bi2Se3 against forming junctions with VSe2, efficient ultrafast hot electron transfer from VSe2 to Bi2Se3 across the interface, significantly shortened metastable carrier lifetimes in Bi2Se3 due to dipole interactions enabling efficient current flow, and the electronic level shift (~tens meV) of bulk states of Bi2Se3 caused by interfacial interactions, which is ~10 times lower compared to conventional 3D electrodes, implying weak Fermi level pinning. Our observations confirm VSe2 as an ideal electrode for efficient Bi2Se3-based-applications with full utilization of topological insulator characteristics.