Coherent phonon spectroscopy and interlayer modulation of charge density wave order in the kagome metal CsV3Sb5

The recent discovery of the AV(3)Sb(5) (A = K, Rb, Cs) material family offers an exciting opportunity to investigate the interplay of correlations, topology, and superconductivity in kagome metals. The low-energy physics of these materials is dominated by an unusual charge density wave phase, but little is understood about the true nature of the order parameter. In this work, we use a combination of ultrafast coherent phonon spectroscopy and first-principles density functional theory calculations to investigate the charge density wave order in CsV3Sb5. We find that the charge density wave is the result of a simultaneous condensation of three optical phonon modes at one M and two L points. This distortion can be described as tri-hexagonal ordering with an interlayer modulation along the c axis. It breaks the C-6 rotational symmetry of the crystal and may offer a natural explanation for reports of uniaxial order at lower temperatures in this material family.

Automated summary

The discovery of the AV(3)Sb(5) material family has provided an exciting opportunity to study correlations, topology, and superconductivity in kagome metals. This study used coherent phonon spectroscopy and density functional theory calculations to investigate the charge density wave order in CsV3Sb5, revealing a tri-hexagonal ordering with interlayer modulation and providing a possible explanation for uniaxial order at lower temperatures in this material family.