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 BaFe2Al9 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 BaCo2Al9. 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 BaFe2Al9 develops a structural modulation instead at low temperature instead of magnetic order.
@article{arxiv.2101.00321,
title = {A catastrophic charge density wave in BaFe$_2$Al$_9$},
author = {William R. Meier and Bryan C. Chakoumakos and Satoshi Okamoto and Michael A. McGuire and Raphaël P. Hermann and German D. Samolyuk and Shang Gao and Qiang Zhang and Matthew B. Stone and Andrew D. Christianson and Brian C. Sales},
journal= {arXiv preprint arXiv:2101.00321},
year = {2021}
}
Comments
34 pages, 8 figures Edits to text as well as figures 2 and 5. Added neutron diffraction (Fig. 6)