$\pi$ Phase Interlayer Shift and Stacking Fault in the Kagome Superconductor CsV${}_3$Sb${}_5$

Abstract

The stacking degree of freedom is a crucial factor in tuning material properties and has been extensively investigated in layered materials. The kagome superconductor CsV${}_3$Sb${}_5$ was recently discovered to exhibit a three-dimensional CDW phase below TCDW ~94 K. Despite the thorough investigation of in-plane modulation, the out-of-plane modulation has remained ambiguous. Here, our polarization- and temperature-dependent Raman measurements reveal the breaking of C${}_6$ rotational symmetry and the presence of three distinct domains oriented at approximately 120°to each other. The observations demonstrate that the CDW phase can be naturally explained as a 2c staggered order phase with adjacent layers exhibiting a relative $\pi$ phase shift. Further, we discover a first-order structural phase transition at approximately 65 K and suggest that it is a stacking order-disorder phase transition due to stacking fault, supported by the thermal hysteresis behavior of a Cs-related phonon mode. Our findings highlight the significance of the stacking degree of freedom in CsV${}_3$Sb${}_5$ and offer structural insights to comprehend the entanglement between superconductivity and CDW.

arXiv commentThis manuscript was published in Phys. Rev. Lett

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• Constrains on s and d components of electron boson coupling constants in one band d wave Eliashberg theory for high Tc superconductors
• Correlation between optical phonon softening and superconducting $T_c$ in YBa${}_2$Cu${}_3$O${}_x$ within $d$-wave Eliashberg theory
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• Magnetic field-induced momentum-dependent symmetry breaking in a kagome superconductor
• Role of On-site and Inter-site Coulomb Interactions in KV${}_3$Sb${}_5$: A first-principles DFT+$U$+$V$ study
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