Incommensurate charge-stripe correlations in the kagome superconductor CsV₃Sb_5−xSn_x

The class of AV₃Sb₅ (A = K, Rb, Cs) kagome metals hosts unconventional charge density wave states seemingly intertwined with their low temperature superconducting phases. The nature of the coupling between these two states and the potential presence of nearby, competing charge instabilities however remain open questions. This phenomenology is strikingly highlighted by the formation of two ‘domes’ in the superconducting transition temperature upon hole-doping CsV₃Sb₅.[1]

Here, we use synchrotron single crystal X-ray diffraction experiments to directly track the evolution of charge correlation as holes are introduced in the system via Sn-substitution on the Sb-site to form CsV₃Sb_5−xSn_x. We select a sample with low Sn-doping (x = 0.025, Fig. 1a) within the first superconducting dome and a sample with higher doping (x = 0.15, Fig. 1b) representing the second dome to compare the charge correlations.

Superlattice reflections at half-integer positions in the sample with low doping (x = 0.025, Fig. 1a) indicate the presence of 2x2 in-plane charge density wave correlations from the parent compound CsV₃Sb₅. In contrast, the sample with higher doping (x = 0.15, Fig. 1b) shows a collapse of the long-range ordered correlations into incommensurate charge-stripes. We observe 3 quasi-1D domains rotated 120° to each other in real space. Those domains origin from the twinned orthorhombic structure of the parent material [2] and vanish upon warming (Fig. 1c).

We further employ scanning tunneling microscopy on the higher doped sample. One-dimensional, stripe-like features are apparent in the STM topograph and can be quantified in the Fourier transform image (Fig. 1d). This Fourier map confirms the absence of half-integer charge density wave order and reveals quasi-1D correlations along one of the atomic Bragg positions. In contrast to the 3 observed domains in bulk x-ray scattering, the scanning tunneling microscope viewing area is small enough to isolate a single twin.

Our experiments establish AV₃Sb₅ as a promising platform for the studies of charge-stripe physics and draw comparisons with the extensively studied 4a0 charge ordering in cuprates.[3] For example, the sizable doping dependence of charge ordering in Bi-based cuprates[4] appears qualitatively similar to observations in CsV₃Sb_5−xSn_x. Given the suppression of charge ordering in cuprates in the overdoped regime, it will be of interest to explore the fate of stripe-like correlations in CsV₃Sb₅ at an even higher doping level, as samples with higher Sn composition are developed in the future and the multigap superconducting phase is completely suppressed. We published our work in npj Quantum Materials.[5]

References

[1] Oey, Ortiz, Kaboudvand, Frassineti, Garcia, Cong, Sanna, Mitrovic, Seshadri and Wilson, Phys. Rev. Mater. 6 (2022) L041801.

[2] Kautzsch, Ortiz, Mallayya, Plumb, Pokharel, Ruff, Islam, Kim, Seshadri and Wilson, Phys. Rev. Mater. 7 (2023) 024806.

[3] Comin and Damascelli, Annu. Rev. Condens. Matter Phys. 7 (2016) 369–405.

[4] Da Silva Neto, Aynajian, Frano, Comin, Schierle, Weschke, Gyenis, Wen, Schneeloch, Xu, Ono, Gu, Le Tacon and Yazdani, Science 343 (2014) 393–396.

[5] Kautzsch, Oey, Li, Ren, Ortiz, Pokharel, Seshadri, Ruff, Kongruengkit, Harter, Wang, Zeljkovic and Wilson, npj Quantum Materials 8 (2023) 37.