NMR Evidence for Universal Pseudogap Behavior in Quasi-Two-Dimensional FeSe-Based Superconductors
B. L. Kang1†, M. Z. Shi1†, D. Zhao1, S. J. Li1, J. Li1, L. X. Zheng1, D. W. Song1, L. P. Nie1, T. Wu1,2,3,4,5*, and X. H. Chen1,2,3,4,5*
1Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, China 2Key Laboratory of Strongly coupled Quantum Matter Physics, Department of Physics, University of Science and Technology of China, Hefei 230026, China 3CAS Center for Excellence in Superconducting Electronics (CENSE), Shanghai 200050, China 4Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China 5Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
Abstract：Recently, by intercalating organic ions into bulk FeSe superconductors, two kinds of layered FeSe-based superconductors [(TBA)$_{x}$FeSe and (CTA)$_{x}$FeSe] with superconducting transition temperatures ($T_{\rm c}$) above 40 K have been discovered. Due to the large interlayer distance ($\sim $15 Å), these new layered superconductors have a large resistivity anisotropy analogous to bismuth-based cuprate superconductors. Moreover, remarkable pseudogap behavior well above $T_{\rm c}$ is revealed by nuclear magnetic resonance (NMR) measurements on $^{77}$Se nuclei, suggesting a preformed pairing scenario similar to that of cuprates. Here, we report another new kind of organic-ion-intercalated FeSe superconductor, (PY)$_{x}$FeSe, with a reduced interlayer distance ($\sim $10 Å) compared to (TBA)$_{x}$FeSe and (CTA)$_{x}$FeSe. By performing $^{77}$Se NMR and transport measurements, we observe a similar pseudogap behavior well above $T_{\rm c}$ of $\sim $40 K and a large resistivity anisotropy of $\sim$$10^{\boldsymbol{4}}$ in (PY)$_{x}$FeSe. All these facts strongly support a universal pseudogap behavior in these layered FeSe-based superconductors with quasi-two-dimensional electronic structures.
. [J]. 中国物理快报, 2022, 39(12): 127401-127401.
B. L. Kang, M. Z. Shi, D. Zhao, S. J. Li, J. Li, L. X. Zheng, D. W. Song, L. P. Nie, T. Wu, and X. H. Chen. NMR Evidence for Universal Pseudogap Behavior in Quasi-Two-Dimensional FeSe-Based Superconductors. Chin. Phys. Lett., 2022, 39(12): 127401-127401.
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