Unconventional charge density wave in Kagome metal BaFe2Al9

TL;DR

This study reveals that BaFe2Al9 exhibits an unconventional, pressure-enhanced charge density wave with a first-order transition, driven by electron correlations rather than Fermi-surface nesting, making it a unique 3D Kagome system for exploring exotic quantum states.

Contribution

It demonstrates that BaFe2Al9 shows pressure-induced enhancement of CDW order with anomalous lattice behavior, highlighting a new mechanism dominated by electron-electron and electron-phonon interactions.

Findings

Pressure increases T_CDW from ~110 K to room temperature.

Lattice expansion and cracking indicate a first-order transition.

Dome-shaped resistance suggests competing electronic phases.

Abstract

The charge density wave (CDW) is a macroscopic quantum state characterized by long-range lattice distortion and modulated charge density. Conventionally, CDWs compete with other electronic orders (e.g. superconductivity) and are suppressed under hydrostatic pressure. Intriguingly, the Kagome-variant metal BaFe2Al9, crystallized in a three-dimensional structure, exhibits pressure-enhanced CDW ordering, where the transition temperature (TCDW) rises from ~110 K to room temperature near 3.6 GPa. The lattice structure was checked by both powder and single crystal x-ray diffraction (XRD). The XRD data reveals an abnormal lattice expansion along a axis near 4-5 GPa upon compression. The strongly suppressed diffraction intensity and splitting diffraction spots from single crystal indicates cracking and breakdown to smaller pieces, indicative of an intrinsic first-order transition character. This anomalous response implies a CDW mechanism dominated by electron-electron and/or electron-phonon correlations, distinct from Fermi-surface nesting in conventional systems. Concomitant dome-shaped pressure-dependent resistance suggests competing electronic phases. Our work establishes BaFe2Al9 as a 3D Kagome platform with unconventional CDW behavior and strong electron-phonon coupling, which provides an alternative platform to explore the electron correlation induced exotic electronic states and other potential emergent quantum phenomenon.