Itahashi Yuki M, Nohara Yamato, Chazono Michiya, Matsuoka Hideki, Arioka Koichiro, Nomoto Tetsuya, Kohama Yoshimitsu, Yanase Youichi, Iwasa Yoshihiro, Kobayashi Kaya
RIKEN Center for Emergent Matter Science (CEMS), Wako, Japan.
Quantum-Phase Electronics Center (QPEC) and Department of Applied Physics, The University of Tokyo, Tokyo, Japan.
Nat Commun. 2025 Jul 31;16(1):7022. doi: 10.1038/s41467-025-62297-6.
Two-dimensional (2D) superconductors are known for their novel emergent phenomena, however, lack of experimental probes beyond resistivity has hindered further exploration of diverse superconducting states. Bulk 2D superconductors, with superconducting layers separated by non-superconducting layers, offer a unique opportunity to break this limit. Here, we synthesized a single crystal of misfit layered compound (PbSe)(NbSe), composed of alternately stacked tri-layer NbSe and non-superconducting block layers with incompatible unit cells. Due to its unique structure, 2D Ising superconductivity is maintained even in a bulk form. Resistivity and tunnel diode oscillator measurements reveal two distinct superconducting phases in magnetic field vs. temperature phase diagram. A theoretical analysis suggests that a layer-selective Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state is realized at the high-magnetic-field phase, where Ising and finite-q superconductivity are mixed due to the tri-layer structure. Bulk 2D superconductors with misfit structure offer a novel opportunity for understanding of 2D superconductivity through bulk measurements and interlayer engineering.
二维（2D）超导体以其新颖的涌现现象而闻名，然而，除了电阻率之外缺乏实验探测手段阻碍了对多种超导态的进一步探索。具有由非超导层分隔的超导层的块状二维超导体提供了打破这一限制的独特机会。在这里，我们合成了一种失配层状化合物（PbSe）（NbSe）的单晶，它由交替堆叠的三层NbSe和具有不相容晶胞的非超导块层组成。由于其独特的结构，二维伊辛超导即使在块状形式下也能得以维持。电阻率和隧道二极管振荡器测量揭示了磁场与温度相图中的两个不同超导相。理论分析表明，在高磁场相中实现了层选择性的富尔德 - 费雷尔 - 拉金 - 奥夫钦尼科夫（FFLO）态，由于三层结构，伊辛超导和有限q超导在此混合。具有失配结构的块状二维超导体通过块状测量和层间工程为理解二维超导提供了新的机会。
