Pressure-induced topological changes in the Fermi surface of a two-dimensional molecular conductor

We demonstrated x-ray structural analysis of the pressure-induced superconductor beta'-ET2ICl2 under extremely high pressure conditions, where ET denotes bis(ethylenedithio)tetrathiafulvalene. This material has been known as the highest transition temperature (Tc) superconductor among organic superconductors (Tc = 14.2 K at 8.2 GPa). On the basis of the experimental results, ab initio models were derived using the constrained random phase approximation. We revealed that the Lifshitz transition exists behind the Mott insulator-imetal transition and found that the value of the on-site Coulomb interaction was halved to around 10 GPa compared to that at ambient pressure. This Letter clarifies the enigmatic origins of high Tc and, concurrently, provides an understanding of the impacts of structural alterations in organic materials under high pressure on their electronic properties and the superconductivity process.