Intercalation-Induced Monolayer Behavior in Bulk NbSe₂

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 NbSe₂ 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 NbSe₂ by expanding the interlayer distance, thereby making intercalated NbSe₂ behave similarly to monolayer NbSe₂. The interlayer distances of NbSe₂ intercalated with THA⁺, CTA⁺, and TDA⁺ cations are almost double or triple that of pristine NbSe₂. The superconducting transition temperature (T_c) of THA-NbSe₂ is comparable to that of pristine NbSe₂, while the charge density wave (CDW) transition temperature is higher. The T_c of intercalated NbSe₂ 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 NbSe₂ significantly exceeds the Pauli paramagnetic limit, which is similar to the Ising superconductivity observed in monolayer NbSe₂. 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.