Synthesis and Electronic Structure of the Fractionally Occupied Double Perovskite EuTa₂O₆ with Ordered Europium Vacancies

2D electronic states underline a wide range of exotic phenomena and provide potential for electronic devices. The ability to create and control these states often requires physical thinning or highly perfect interfaces. In this work, the “fractional double perovskite” ATa₂O₆ (A: Eu²⁺) is synthesized and characterized, where alternating A‐site cations and A‐site vacancies significantly impact the electronic structure, giving rise to a quasi‐2D electronic state within a 3D crystal framework. The intrinsic crystal anisotropy of ATa₂O₆ plays a pivotal role, underscoring how targeted structural modifications can facilitate the emergence of novel quantum states. Utilizing single‐crystal synthesis via molecular‐beam epitaxy, the crystal and electronic structures of ATa₂O₆ are investigated. X‐ray diffraction and electron microscopy reveal the layered A‐site ordering. Synchrotron‐based diffraction shows the presence of three epitaxial twin variants of ATa₂O₆ domains, with preferential orientation along out‐of‐plane direction. Angle‐resolved photoemission spectroscopy, along with density functional theory calculations, provide direct insight into the electronic structure, unveiling the potential for engineered confined states within bulk materials. These findings highlight ATa₂O₆ as a platform for studying 2D‐like electronic phenomena in a 3D context, paving the way for novel device architectures.