Competing charge-density wave instabilities in the kagome metal ScV6Sn6

Abstract

Owing to its unique geometry, the kagome lattice hosts various many-body quantum states including frustrated magnetism, superconductivity, charge-density waves (CDWs), and topologically nontrivial phases of matter. Kagome metals with 2×2 CDWs, corresponding to the nesting of van Hove saddle points, are found to exhibit a number of exotic electronic phases, and have been the focus of much recent research. More recently, a √3×√3 CDW was discovered in the kagome metal ScV6Sn6 below TCDW≈91 K, whose underlying mechanism and formation process remain unclear, particularly in comparison with the 2×2 kagome CDWs. Using inelastic X-ray scattering, we discover a short-range √3×√3×2 CDW that is dominant in ScV6Sn6 well above TCDW, distinct from the √3×√3×3 CDW below TCDW. The short-range CDW grows upon cooling, and is accompanied by the softening of phonons, indicative of its dynamic nature. As the √3×√3×3 CDW appears, the short-range CDW becomes suppressed, revealing a competition between these CDW instabilities. The competing CDW instabilities in ScV6Sn6 lead to an unusual CDW formation process, with the most pronounced phonon softening and the static CDW occurring at different wavevectors. Our first-principles calculations indicate that the √3×√3×2 CDW is energetically favored, consistent with experimental observations at high temperatures. However, the √3×√3×3 CDW is selected as the ground state due to a large wavevector-dependent electron-phonon coupling (EPC), which also accounts for the enhanced electron scattering above TCDW. Our findings reveal the dominance of EPC-driven correlated many-body physics in ScV6Sn6, making it an ideal system to study emergent quantum matter in the strong EPC regime.

Universal sublinear resistivity in vanadium kagome materials hosting charge density waves

“…Curiously, above T CDW the slope of ρ zz (T ) changes from positive (metal-like) to negative (insulator-like) as the field is increased through 5 T. This temperature-dependent enhancement of ρ zz above T CDW may originate from strong CDW fluctuations that are recently reported in Ref. 27 . This dramatic magnetoresistance behavior is clearly absent in LuV 6 Sn 6 , revealing the anisotropic impact of CDW order and fluctuations on transport in ScV 6 Sn 6 .…”

“…The CDW in ScV 6 Sn 6 has some unique characteristics. There are strong CDW fluctuations above the CDW transition with a different period than the low temperature ordered phase 27 demonstrating competing CDW modes 28 . The magnetic susceptibility 17 and optical conductivity 29 reveal a drop in the number of carriers on cooling through T CDW .…”

Tiny Sc Allows the Chains to Rattle: Impact of Lu and Y Doping on the Charge-Density Wave in ScV6Sn6

“…The Sc and Sn1 atoms in the first column show taller ellipsoids, representing larger position deviations in this direction. This reflects the strong CDW fluctuation observed in ScV 6 Sn 6 by inelastic and diffuse X-ray scattering. ,, …”

“…Rare earth atoms and Sn1 atoms form a chain that occupies channels in the hexagonal holes in the kagome and honeycomb layers, as illustrated in Figure b. These chains of atoms play a pivotal role in the CDW mode as they displace along the c -axis in the modulated structure. , Several CDW modes appear to compete in ScV 6 Sn 6 demonstrated by the strong CDW fluctuations observed above the transition temperature ,, with impacts on the electrical transport properties…”

“…It is important to note that the CDW in ScV 6 Sn 6 has a wave vector ,, in contrast to that observed in the AV 3 Sb 5 materials . ,,− ,, Another key difference is that the CDW in AV 3 Sb 5 compounds is dominated by vanadium displacements perpendicular to the hexagonal c -axis . Numerous investigations of the electronic structure of ScV 6 Sn 6 by photoemission measurements tie the CDW order to the Sn bands instead of the prominent vanadium bands. ,− There is evidence that the CDW phase has unusual characteristics including anomalous Hall-like responses , and claims of time reversal symmetry breaking …”