Artem Korshunov

Electronic, magnetic, and lattice degrees of freedom are often strongly intertwined in quantum materials, giving rise to competing ordered states and emergent collective phenomena. Understanding how these interactions evolve across symmetry-breaking transitions is essential for identifying new mechanisms of electronic ordering. Here, we show that the antiferromagnet chromium antimonide provides an ideal platform to investigate this interplay and uncover short-range charge-order fluctuations at the M point of the Brillouin zone, q * = ( 1 2   0 ) , persisting well above the Néel temperature, T _N . These fluctuations collapse upon entering the magnetically ordered phase, revealing a direct competition between charge and spin order parameters. At T _N , the phonon dispersion at q * develops a pronounced Kohn-like anomaly, signaling strong electron-phonon coupling in the vicinity of the magnetic transition. Below T _N , exchange striction markedly renormalizes the associated soft phonon mode by ∼6 milli–electron volts, corresponding to the largest spin-phonon coupling reported to date. First-principles calculations show that the relevant phonon branch is unstable at the harmonic level only in the absence of magnetic order, highlighting the remarkable sensitivity of the lattice to magnetic symmetry breaking. The suppression of charge correlations upon magnetic ordering, together with the abrupt reconstruction of the phonon spectrum at T _N , demonstrates an exceptional coupling between charge, spin, and lattice degrees of freedom in chromium antimonide. With its chemically simple structure and symmetry-protected altermagnetic state, chromium antimonide emerges as a model system for exploring giant spin-phonon coupling, competing electronic instabilities, and emergent broken symmetries in altermagnetic materials.

Charge-density-wave (CDW) order and superconductivity coexist in the kagome metals AV ₃ Sb ₅ (A=K, Cs, Rb), raising fundamental questions about the mechanisms driving their intertwined phases. Here we combine high-resolution inelastic X-ray scattering with first-principles calculations to uncover the origin of CDW formation in CsV ₃ Sb ₅ . Guided by structure factor analysis, we identify a soft phonon mode along the reciprocal M - L direction, with the strongest effect at the L point, where the elastic scattering intensity also grows most rapidly upon cooling. First-principles calculations incorporating lattice anharmonicity and electron-phonon coupling reproduce these observations and establish a soft-mode instability at the L point as the driving mechanism of CDW formation. Despite the weakly first-order character of the transition, our results unambiguously demonstrate that the CDW in CsV ₃ Sb ₅ originates from a softened phonon, clarifying its microscopic origin and highlighting the central role of lattice dynamics in kagome metals.

Magnon-phonon hybridization in ordered materials is a crucial phenomenon with significant implications for spintronics, magnonics, and quantum materials research. We present direct experimental evidence and theoretical insights into magnon-phonon coupling in Mn_{3}Ge, a kagome antiferromagnet with noncollinear spin order. Using inelastic x-ray scattering and ab initio modeling, we uncover strong hybridization between planar spin fluctuations and transverse optical phonons, resulting in a large hybridization gap of ∼2 meV. This coupling is driven by interlayer Heisenberg exchange interactions and is enhanced by the material's symmetry and magnetic frustration. The simplicity of the Mn_{3}Ge structure enables clear identification of the hybridized modes, bridging theoretical predictions and experimental observations. Our findings establish Mn_{3}Ge as a model system for exploring magnon-phonon interactions and offer a pathway for designing materials with tunable magnetoelastic properties.