Orthorhombic charge density wave on the tetragonal lattice of EuAl4

EuAl4 possesses the BaAl4 crystal structure type with tetragonal symmetry I4/mmm. It undergoes a charge density wave (CDW) transition at TCDW = 145 K and features four consecutive antiferromagnetic phase transitions below 16 K. Here we use single-crystal X-ray diffraction to determine the incommensu...

Full description

Saved in:
Bibliographic Details
Published in:IUCrJ 2022-05, Vol.9 (3), p.378-385
Main Authors: Ramakrishnan, Sitaram, Kotla, Surya Rohith, Toms Rekis, Jin-Ke, Bao, Eisele, Claudio, Noohinejad, Leila, Tolkiehn, Martin, Paulmann, Carsten, Singh, Birender, Verma, Rahul, Bag, Biplab, Kulkarni, Ruta, Arumugam Thamizhavel, Singh, Bahadur, Ramakrishnan, Srinivasan, Sander van Smaalen
Format: Article
Language:English
Subjects:
Antiferromagnetism
aperiodic structures
Broken symmetry
charge density wave
Charge density waves
Crystal lattices
Crystal structure
density functional theory
inorganic materials
modulated
Modulation
Phase transitions
Research Papers
Single crystals
Subgroups
superspace
Symmetry
Temperature dependence
Tetragonal lattice
twinning
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:EuAl4 possesses the BaAl4 crystal structure type with tetragonal symmetry I4/mmm. It undergoes a charge density wave (CDW) transition at TCDW = 145 K and features four consecutive antiferromagnetic phase transitions below 16 K. Here we use single-crystal X-ray diffraction to determine the incommensurately modulated crystal structure of EuAl4 in its CDW state. The CDW is shown to be incommensurate with modulation wave vector q = (0,0,0.1781 (3)) at 70 K. The symmetry of the incommensurately modulated crystal structure is orthorhombic with superspace group Fmmm(00σ)s00, where Fmmm is a subgroup of I4/mmm of index 2. Both the lattice and the atomic coordinates of the basic structure remain tetragonal. Symmetry breaking is entirely due to the modulation wave, where atoms Eu and Al1 have displacements exclusively along a, while the fourfold rotation would require equal displacement amplitudes along a and b. The calculated band structure of the basic structure and interatomic distances in the modulated crystal structure both indicate the Al atoms as the location of the CDW. The tem­per­ature dependence of the specific heat reveals an anomaly at TCDW = 145 K of a magnitude similar to canonical CDW systems. The present discovery of orthorhombic symmetry for the CDW state of EuAl4 leads to the suggestion of monoclinic instead of orthorhombic symmetry for the third AFM state.
ISSN:2052-2525
2052-2525
DOI:10.1107/S2052252522003888