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arXiv · 2509.09903

Evolution from Topological Dirac Metal to Flat-band-Induced Antiferromagnet in Layered KxNi4S2 (0<=x<=1)

Hengdi Zhao·Xiuquan Zhou·Hyowon Park·Tianqi Deng·Brandon Wilfong·Alann P. Au II·Samuel E. Pate·Craig M. Brown·Hui Wu·Tushar Bhowmick·Tessa McNamee·Ravhi Kumar·Yu-Sheng Chen·Zhi-Li Xiao·Russell Hemley·Weizhao Cai·Shanti Deemyad·Duck-Young Chung·Stephan Rosenkranz·Mercouri G. Kanatzidis
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Abstract

Condensed matter systems with coexisting Dirac cones and flat bands, and a switchable control between them within a single system, are desirable but remarkably uncommon. Here we report a layered quantum material system, KxNi4S2 (0 <= x <= 1), that simultaneously hosts both characteristics without involving typical Kagome/honeycomb lattices. Enabled by a topochemical K-deintercalation process, the Fermi surface can be fine-tuned continuously over a wide range of energies. Consequently, a non-magnetic Dirac-metal state with a topological nontrivial Z2 index of 1;(000), supported by first-principles calculations and high mobility up to 1471 cm2V-1s-1, is observed on the K-rich x = 1 side, whereas a flat-band induced antiferromagnetic state with TN up to 10.1 K emerges as K-content approaches 0. The KxNi4S2 system offers a versatile platform for exploring emerging phenomena and underscores a viable pathway for in-situ control of quantum materials dominated by Dirac cones, flat bands, and their interplay.

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Hengdi Zhao, Xiuquan Zhou, Hyowon Park, Tianqi Deng, Brandon Wilfong, Alann P. Au II, Samuel E. Pate, Craig M. Brown, Hui Wu, Tushar Bhowmick, Tessa McNamee, Ravhi Kumar, Yu-Sheng Chen, Zhi-Li Xiao, Russell Hemley, Weizhao Cai, Shanti Deemyad, Duck-Young Chung, Stephan Rosenkranz, Mercouri G. Kanatzidis. 2025-09-12. Evolution from Topological Dirac Metal to Flat-band-Induced Antiferromagnet in Layered KxNi4S2 (0<=x<=1). https://doi.org/10.1016/j.matt.2025.102418

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