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TT: Fachverband Tiefe Temperaturen
TT 13: Kagome Systems
TT 13.4: Vortrag
Montag, 18. März 2024, 15:45–16:00, H 3010
Order-by-disorder charge density wave condensation at q=(1/3,1/3,1/3) in kagome metal ScV6Sn6 — •Alaska Subedi — CPHT, CNRS, Ecole Polytechnique, IP Paris, Palaiseau, France
The recent discovery of a charge density wave order at the wave vector P (1/3, 1/3, 1/3) in the kagome metal ScV6Sn6 has created a mystery because subsequent theoretical and experimental studies show a dominant phonon instability instead at another wave vector H (1/3,1/3,1/2). Here, I discuss the results of first principles total energy calculations that were used to map out the landscape of the structural distortions due to the unstable phonon modes at H, L (1/2,0,1/2), and P present in this material. In agreement with previous results, I find that the distortions due to the H instability cause the largest gain in energy relative to the parent structure, followed in order by the L and P instabilities. However, only two distinct structure occur due to this instability, which are separated by 6 meV/f.u. The instability at L results in three distinct structures separated in energy by 5 meV/f.u. In contrast, six different distorted structures are stabilized due to the instability at P, and they all lie within 2 meV/f.u. of each other. Hence, despite a lower energy gain, the condensation at P could be favorable due to a larger entropy gain associated with the fluctuations within a manifold with larger multiplicity via the order-by-disorder mechanism.
Keywords: charge density wave; phonon instabilities