Transitory Topochemical Tailoring of a van der Waals Superconductor.

Topochemical intercalation is widely used to access metastable phases with novel electronic properties, but the reverse reaction (deintercalation) typically restores the original state, limiting practical use. Here, we present a topochemical approach that employs a sacrificial intercalant that thermally decomposes to irreversibly lock in the new electronic state. Using 2-aminobutane as the sacrificial intercalant, we convert the van der Waals (vdW) material 1T-TiSe2 into a superconductor and the vdW superconductor 2H-NbSe2 into a nonsuperconducting metal, while preserving the ability to exfoliate the resulting crystals. We find that this transitory intercalation increases the electron density in both materials and partially suppresses the CDW in TiSe2. By tuning the thermolysis temperature, we can systematically vary the carrier density in TiSe2, enabling us to map its phase diagram. The superconductivity in TiSe2 is retained in exfoliated flakes, although with a lower critical temperature. This transitory topochemical strategy enables access to new electronic states with precisely tuned carrier densities that are otherwise inaccessible through direct solid-state synthesis.