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Série d'événement : Séminaire MCBT

Sander VAN SMAALEN (Laboratory of Crystallography, Bayerisches Geoinstitut, University of Bayreuth)

30 mars @ 14:00

Chiral charge density waves in EuAl4 and related compounds

Résumé :

The BaAl 4 structure type has centrosymmetric, tetragonal symmetry, I4/mmm, with three crystallographically independent atom sites: Ba, Al1 and Al2. Solid solution series RAl 4-x Gax (R= Eu, Sr, Ca, Ba; 0 < x < 4) crystallize in this structure type [1], where Ga preferably occupies the Al2 site. Accordingly, complete chemical order is found for x = 0, 2, 4. Incommensurate charge-density waves (CDWs) have been observed in several of these ordered compounds. For the other values of x, lack of chemical order leads to suppression of the CDW transition. At much lower temperatures (T = 10–30 K) magnetic order appears for the compounds with magnetic Eu atoms. Here, we present the crystal structures of the incommensurate CDWs of EuAl 4 , EuAl 2 Ga2 and SrAl 4 . In particular, the symmetry of the CDWs is analyzed in view of x-ray diffraction data (present data [2–5]), and results of transmission electron microscopy (TEM), density functional theory (DFT) calculations and inelastic x ray scattering (IXS) from the literature [6–8].

References :

[1] M. Stavinoha et al., Phys. Rev. B 97, 195146 (2018). Charge density wave behavior and order-disorder in the antiferromagnetic metallic series Eu(Ga1-x Al x )4 .
[2] S. Ramakrishnan et al., IUCrJ 9, 378–385 (2022). Orthorhombic charge density wave on the tetragonal lattice of EuAl 4 .
[3] S. R. Kotla et al., Phys. Rev. B 112, 064113 (2025). Broken inversion symmetry in the charge density wave phase in EuAl 4 .
[4] S. Ramakrishnan et al., Phys. Rev. Research 6, 023277 (2024). Non-centrosymmetric, transverse structural modulation in SrAl 4 , and elucidation of its origin in the BaAl 4 family of
compounds.
[5] H. Agarwal et al., Phys. Rev. B 111, 155144 (2025). I-centered versus F-centered orthorhombic symmetry and negative thermal expansion of the charge density wave of EuAl2 Ga2 .
[6] H. Ni et al., Phys. Rev. Mater. 8, 104414 (2024). Real-space visualization of atomic displacements in a long-wavelength charge density wave using cryogenic 4D-STEM.
[7] A. N. Korshunov et al., Phys. Rev. B 110, 045102 (2024). Phonon softening and atomic modulations in EuAl 4 .
[8] F. Z. Yang et al., Nature Commun. 16, 10401 (2025). Incommensurate Transverse Peierls Transition and Signature of Chiral Charge Density Wave in EuAl4

Contact : andrew.fefferman@neel.cnrs.fr

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