New Organic Crystalline Material Close to Nodal-Line Materials: α′-STF2IBr2

Abstract

Recently, topological materials (TMs) have attracted attention from various scientists. Their electronic properties are governed by relativistic particles called Dirac fermions which, in some cases, possess no masses and move in solids with the speed of light. In addition to the unique particles, such materials exhibit unprecedented electronic properties because of the quantum effects (interference between wavefunctions). Examples include nodal-line materials (NLMs), where metallic or even superconducting properties may appear only at the surface of the single crystals of insulators. Thus far, whether they be organic or inorganic compounds, TMs have hardly been discovered except for the zero-gap conductors (ZGCs), because there is no guideline on how to develop such unusual materials. In this work, we prepared a new organic charge–transfer complex, α′-STF2IBr2 (STF = bis(ethylenedithio)diselenadithiafulvalene), which measured the electrical and magnetic properties and calculated the band structure and intermolecular interactions. A close comparison with those of α-STF2I3, being established as a ZGC at p > 12–15 kbar, revealed that α′-STF2IBr2 is also closely related to it, but belongs to a different type of TMs, namely NLMs. This finding will accelerate the successive findings of NLMs to elucidate the mechanism of their unique electronic properties.