Intercalation-Induced Monolayer Behavior in Bulk NbSe.

Superconductivity at the 2D limit is significant for advancing fundamental physics, leading to extensive research on monolayer two-dimensional materials. In particular, monolayer transition metal dichalcogenides such as NbSe exhibit Ising superconductivity due to broken in-plane inversion symmetry and strong spin-orbit coupling, which has garnered significant attention. In this letter, we adopted an organic cation intercalation technique to modulate the interlayer interaction of NbSe by expanding the interlayer distance, thereby making intercalated NbSe behave similarly to monolayer NbSe. The interlayer distances of NbSe intercalated with THA, CTA, and TDA cations are almost double or triple that of pristine NbSe. The superconducting transition temperature () of THA-NbSe is comparable to that of pristine NbSe, while the charge density wave (CDW) transition temperature is higher. The of intercalated NbSe decreases with a reduced hole concentration, and the enhanced CDW is ascribed to the dimensional reduction. Notably, the in-plane upper critical field of intercalated NbSe significantly exceeds the Pauli paramagnetic limit, which is similar to the Ising superconductivity observed in monolayer NbSe. Our work demonstrates that the organic cations intercalated two-dimensional materials exhibit behavior similar to their monolayer counterparts, providing a convenient platform for exploring and modulating physical phenomena at the two-dimensional limit.