I will present recent progress in ARPES investigation on n-type cuprates and superconducting nickelates, made possible by in-situ MBE grown thin films [1, 2].

Electron-doped cuprates provide a critical test of the relationship between strange-metal behavior and high-temperature superconductivity. Using in-situ angle-resolved photoemission spectroscopy and transport measurements on La₂₋ₓCeₓCuO₄ across the entire superconducting dome, we establish a quantitatively consistent phase diagram through Luttinger-volume-based doping calibration. We find a complete absence of the strange-metal regime above Tc, with transport exhibiting Fermi-liquid-like behavior throughout the phase diagram. This pronounced electron-hole asymmetry demonstrates that strange-metal behavior is not essential for high-temperature superconductivity. By directly correlating spectroscopic and transport properties, we further link the underdoped insulating state to the onset of the pseudogap and identify two competing trends governing the superconducting dome: increasing low-energy spectral weight associated with improved metallicity and weakening correlation-driven interactions. These results provide a unified microscopic and macroscopic picture of electron-doped cuprates and place important constraints on theories of high-temperature superconductivity.

The discovery of superconductivity in compressively strained bilayer nickelate thin films has established a new platform for exploring high-temperature superconductivity beyond the cuprates. We report a systematic in-situ angle-resolved photoemission spectroscopy study of superconducting bilayer nickelate thin films spanning Ca doping, oxygen stoichiometry, growth methods, and film thickness. We find that the low-energy electronic structure is remarkably robust and evolves systematically with epitaxial strain. The 3dz²-derived γ band remains below the Fermi level in undoped superconducting samples, while crossing the Fermi level with additional hole doping, demonstrating that the debated γ-pocket is not a prerequisite for superconductivity. Combined with evidence for strong interlayer hybridization and substantial correlation-driven band renormalization, our results place bilayer nickelates in an intermediate-correlation regime and establish key spectroscopic constraints on microscopic theories of their pairing mechanism.

[1] Absence of strange metal regime and interaction-driven low energy excitations – a Luttinger volume study of an n-type cuprate La_2-xCe_xCuO_4; Ruohan Wang, Chun Lin, Bai Yang Wang, Yong Zhong, Yonghao Yuan, Makoto Hashimoto, DongHui Lu, Dung-Hai Lee, Thomas P. Devereaux, Zhi-Xun Shen; manuscript under review

[2] Electronic structure of compressively strained bilayer nickelate thin film; Bai Yang Wang, Sebastien N. Abadi, Yidi Liu, Yu Zhang, Yong Zhong, Yijun Yu, Berit H. Goodge, Xiaoliang Zhang, Yi-Ming Wu, Ruohan Wang, Jiarui Li, Yaoju Tarn, Eun Kyo Ko, Vivek Thampy, Chun Lin, Makoto Hashimoto, Donghui Lu, Young S. Lee, Thomas P. Devereaux, Chunjing Jia, Harold Y. Hwang, Zhi-Xun Shen; manuscript under review