Observation of layer-dependent uniaxial charge density wave in a noble metal alloy superconductor β-IrSn₄

The AB₄-type intermetallic compounds host a wide range of emergent quantum phenomena, providing a fertile platform for exploring the interplay between crystal structure and electronic orders. Among them, β-IrSn₄ has recently attracted attention as a noble-metal-based layered superconductor with weak interlayer coupling and type-I superconductivity. However, its electronic states and possible symmetry-breaking orders remain largely unexplored on the atomic scale. Here, we report the observation of a layer-dependent uniaxial charge density wave (CDW) in β-IrSn₄ using ultra-low-temperature scanning tunneling microscopy. The charge order appears as stripe-like modulations that break the in-plane C₄ symmetry, and its orientation rotates by 90° between adjacent layers. Spectroscopy measurements reveal a homogeneous superconducting gap coexisting with the layer-dependent CDW, with no detectable modulation from the charge order. First-principles calculations suggest that interlayer coupling induces the observed anisotropic electronic structure. These results reveal a layer-dependent symmetry-breaking electronic state in β-IrSn₄ and highlight the role of interlayer interactions in shaping its electronic properties.