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arXiv · 2609.35091

Low-Temperature Stabilization of $δ$-NbN Superconducting Thin Films through Energy-Selective Ion Beam Sputtering

Yifan Liu·Junwoo Lee·Mingyu Xu·Weiwei Xie·Robert J. Cava·Qi Hua Fan
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Abstract

Achieving high-quality superconducting thin films at low temperatures is a central challenge for scalable quantum device integration and Complementary Metal-Oxide-Semiconductor (CMOS)-compatible fabrication. Here, we demonstrate a room-temperature magnetron sputtering approach for synthesizing niobium nitride (NbN) thin films using a novel energy-selective ion source that enables independent control of ion energy and ion flux. This capability provides a powerful route to precisely tailor surface kinetics and crystallization pathways, overcoming longstanding limitations in stabilizing high-quality NbN at reduced temperatures. The resulting films were characterized by superconducting transport measurements, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Compared with conventional reactive sputtering, ion beam-assisted growth yields a substantial narrowing of the transition width at the superconducting temperature, indicating improved phase purity and electronic homogeneity. Furthermore, this work introduces energy-selective ion control as a general, non-equilibrium route to stabilize metastable superconducting phases at low temperatures, offering a new design paradigm for thin-film quantum materials.

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Yifan Liu, Junwoo Lee, Mingyu Xu, Weiwei Xie, Robert J. Cava, Qi Hua Fan. 2026-09-28. Low-Temperature Stabilization of $δ$-NbN Superconducting Thin Films through Energy-Selective Ion Beam Sputtering. https://arxiv.org/abs/2609.35091

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