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

TL;DR

This study investigates how high pressure alters the Fermi surface and electronic properties of a two-dimensional organic superconductor, revealing a Lifshitz transition and changes in Coulomb interactions that relate to its high transition temperature.

Contribution

It provides the first detailed analysis linking pressure-induced structural changes to topological Fermi surface modifications in organic superconductors.

Findings

Lifshitz transition occurs behind the Mott insulator-metal transition.

On-site Coulomb interaction is halved at around 10 GPa.

High pressure structural changes influence superconductivity in organic materials.

Abstract

We demonstrated X-ray structural analysis of the pressure-induced superconductor, $\beta'$-ET$_2$ICl$_2$ under extremely high-pressure conditions, where ET denotes bis(ethylenedithio)tetrathiafulvalene. This material has been known as the highest transition temperature ($T_c$) superconductor among organic superconductors ($T_c=14.2$ 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-metal 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 study clarifies the enigmatic origins of high $T_{\rm c}$, and concurrently, provides a new understanding of the impacts of structural alterations in organic materials under high pressure on their electronic properties and the superconductivity process.