NbSe2

NbSe₂ (niobium diselenide) is a layered transition‑metal dichalcogenide that crystallises in a hexagonal 2H structure (space group P6₃/mmc). Each layer consists of a hexagonal sheet of Nb atoms sandwiched between two selenium sheets, with strong covalent bonding within the layer and weak van der Waals forces between layers, giving the material a pronounced anisotropy and enabling mechanical exfoliation down to single‑layer thickness.

In its bulk form NbSe₂ is a metallic conductor that exhibits a charge‑density‑wave (CDW) transition near 33 K, where the electron density becomes modulated in a periodic fashion accompanied by a slight lattice distortion. Below 7.2 K the compound enters a superconducting state, coexisting with the CDW order. The superconductivity is characterised by a relatively high critical field and a short coherence length, and it persists in few‑layer and monolayer samples, albeit with a reduced transition temperature that depends on thickness and substrate interactions.

NbSe₂ can be grown by chemical vapor transport, flux techniques, or molecular‑beam epitaxy, and high‑quality single crystals are routinely obtained for fundamental studies. Its layered nature makes it a prototypical system for exploring two‑dimensional physics, quantum interference effects, and vortex dynamics in type‑II superconductors. The material is also of interest for device applications such as superconducting nanowires, photodetectors, and heterostructures with other two‑dimensional crystals, where proximity‑induced phenomena and spin‑orbit coupling can be engineered.

Research continues on tuning its electronic phases via pressure, intercalation, doping, or electrostatic gating, aiming to clarify the interplay between CDW order and superconductivity and to exploit the tunable properties of NbSe₂ in quantum‑technology platforms.