A catastrophic charge density wave in BaFe${}_2$Al${}_9$

Abstract

Charge density waves (CDW) are modulations of the electron density and the atomic lattice that develop in some crystalline materials at low temperature. We report an unusual example of a CDW in BaFe${}_2$Al${}_9$ below 100 K. In contrast to the canonical CDW phase transition, temperature dependent physical properties of single crystals reveal a first-order phase transition. This is accompanied by a discontinuous change in the size of the crystal lattice. In fact, this large strain has catastrophic consequences for the crystals causing them to physically shatter. Single crystal x-ray diffraction reveals super-lattice peaks in the low-temperature phase signaling the development of a CDW lattice modulation. No similar low-temperature transitions are observed in BaCo${}_2$Al${}_9$. Electronic structure calculations provide one hint to the different behavior of these two compounds; the d-orbital states in the Fe compound are not completely filled. Iron compounds are renowned for their magnetism and partly filled d-states play a key role. It is therefore surprising that BaFe${}_2$Al${}_9$ develops a structural modulation instead at low temperature instead of magnetic order.

arXiv comment34 pages, 8 figures Edits to text as well as figures 2 and 5. Added neutron diffraction (Fig. 6)

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• Orthorhombic charge density wave on the tetragonal lattice of EuAl4
• Flat-Band Itinerant Antiferromagnetism in the Kagome Metal CoSn1-xInx
• Coupling between colossal charge density wave ordering and magnetism in Ho2Ir3Si5
• The electronic structure of intertwined kagome, honeycomb, and triangular sublattices of the intermetallics MCo${}_2$Al${}_9$
• Realization of Z${}_2$ Topological Metal in Single-Crystalline Nickel Deficient NiV${}_2$Se${}_4$
• Room temperature charge density wave in a tetragonal polymorph of Gd2Os3Si5 and study of its origin in the RE2T3X5 (RE = Rare earth, T = transition metal, X = Si, Ge) series
• Origin of the charge density wave state in BaFe${}_2$Al${}_9$