The transition-metal dichalcogenides have long fascinated us with their myriad of polytypes, complex band structures and interesting physical properties. Recently there is resurging interest in this family of materials, for their tunable semiconducting and superconducting behaviors. In this talk, I present a novel experiment on the well-known dichalcogenide superconductor 2H-NbSe2, using scanning tunneling microscopy (STM) at 300 mK with an in-plane magnetic field of up to 9 Tesla. The atomic-scale STM spectroscopy enabled direct measurement of the quasiparticle density-of-states spectrum under finite superfluid momentum. The measurement revealed unambiguous evidence for multiband Cooper pairing and a remarkable transition of the in-plane vortex lattice related to the multiband pairing. If time permits, I will also discuss implications of our results on recent studies of the Higgs-Anderson boson modes in 2H-NbSe2, and on its use for generating Majorana fermion states by proximity to topological insulators.
