Local mechanism of valence bond formation in IrTe$_2$

TL;DR

This study reveals that in IrTe$_2$, local valence bond formation is driven by changes in Ir-Te-Ir bond angles under pressure, which may influence its superconducting properties and electron-phonon interactions.

Contribution

The paper uncovers a local mechanism of valence bond formation in IrTe$_2$ driven by bond angle changes, combining high-pressure X-ray diffraction with DFT calculations.

Findings

Valence bond formation correlates with decreased Ir-Te-Ir bond angles.

Structural evolution under pressure stabilizes local valence bonds.

Implications for strong electron-phonon coupling and superconductivity.

Abstract

Doped IrTe$_2$ is considered a platform for topological superconductivity and therefore receives currently a lot of interest. In addition, the superconductivity in these materials exists in close vicinity of electronic valence bond crystals, which we explore here by means of high-pressure single crystal x-ray diffraction in combination with density functional theory. Our crystallographic refinements provide unprecedented information about the structural evolution as a function of applied pressure up to 42 GPa. Using this structural information for density functional theory calculations, we show that the valence bond formation in IrTe$_2$ is driven by changes in the Ir-Te-Ir bond angle. When a valence bond is formed, this bond angle decreases drastically, leading to a stabilization of local valence bonds large enough to push them out of a broad band continuum. This unusual local mechanism of valence bond formation in an itinerant material provides a natural explanation for the different valence bond orders in IrTe$_2$, implies a very strong electron-phonon coupling and is most likely relevant for the superconductivity as well.