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Uniaxial strain-tuning of electronic superlattices in CsV3Sb5

Authors: João Almeida Mendes

Supervisors: Pedro Borlido; Jochen Geck

MSc thesis, UC - Dissertações de Mestrado (supervisores: Pedro Borlido; Jochen Geck) (2025) (2025)

Abstract: This dissertation reports a temperature and strain dependent single-crystal X-ray diffraction study of the kagome metal CsV3Sb5 that probes the superlattice modulations associated with its electronic order. Using an in situ piezoelectric uniaxial strain cell we apply very small compressive strains (<= 0.2) along the hexagonal a direction and follow the evolution of satellite reflections in the high-resolution diffraction pattern. In the high-temperature 2x2x4 CDW phase the satellite intensities change strongly and smoothly even for minute strains: the peaks positions and widths remain essentially unchanged, while intensities redistribute in a manner consistent with a progressive detwinning of the electronic superlattice. From the measurements on the detwinned electronic state we identify the intrinsic character of the 2x2x4 modulation as a double-q electronic order. In contrast, the low-temperature 2x2x2 phase is largely insensitive to small uniaxial strain, indicating a fundamentally different in-plane symmetry, stabilization mechanism, or both. Additional observations include hysteresis upon strain-cycling, CDW memory due to domain-wall pinning, and the detection of new very weak satellite peaks that point to an additional modulation. These results (i) demonstrate controlled detwinning of an electronic superlattice, (ii) reveal distinct strain susceptibilities of the two CDW phases, and (iii) provide an experimental route toward a definitive structural refinement of the 2x2x4 superstructure.