Valence-skipping and quasi-two-dimensionality of superconductivity in a van der Waals insulator

Caorong Zhang, Junwei Huang, Kun Zhai, Keivan Akhtari, Zhiwei Shen, Lingyi Ao, Zeya Li, Feng Qin, Yukai Chang, Ling Zhou, Ming Tang, Xueting Dai, Caiyu Qiu, Yi Zhang, Lin Wang (), Zhongyuan Liu, Yongjun Tian, Mohammad Saeed Bahramy () and Hongtao Yuan ()
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Caorong Zhang: Nanjing University
Junwei Huang: Nanjing University
Kun Zhai: Yanshan University
Keivan Akhtari: University of Kurdistan
Zhiwei Shen: Yanshan University
Lingyi Ao: Nanjing University
Zeya Li: Nanjing University
Feng Qin: Nanjing University
Yukai Chang: Yanshan University
Ling Zhou: Nanjing University
Ming Tang: Nanjing University
Xueting Dai: Nanjing University
Caiyu Qiu: Nanjing University
Yi Zhang: Nanjing University
Lin Wang: Yanshan University
Zhongyuan Liu: Yanshan University
Yongjun Tian: Yanshan University
Mohammad Saeed Bahramy: The University of Manchester
Hongtao Yuan: Nanjing University

Nature Communications, 2022, vol. 13, issue 1, 1-9

Abstract: Abstract Valence fluctuation of interacting electrons plays a crucial role in emergent quantum phenomena in correlated electron systems. The theoretical rationale is that this effect can drive a band insulator into a superconductor through charge redistribution around the Fermi level. However, the root cause of such a fluctuating leap in the ionic valency remains elusive. Here, we demonstrate a valence-skipping-driven insulator-to-superconductor transition and realize quasi-two-dimensional superconductivity in a van der Waals insulator GeP under pressure. This is shown to result from valence skipping of the Ge cation, altering its average valency from 3+ to 4+, turning GeP from a layered compound to a three-dimensional covalent system with superconducting critical temperature reaching its maximum of 10 K. Such a valence-skipping-induced superconductivity with a quasi-two-dimensional nature in thin samples, showing a Berezinskii-Kosterlitz-Thouless-like character, is further confirmed by angle-dependent upper-critical-field measurements. These findings provide a model system to examine competing order parameters in valence-skipping systems.

Date: 2022
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DOI: 10.1038/s41467-022-34726-3

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