| CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES |
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Observation of Coulomb Gap and Enhanced Superconducting Gap in Nano-Sized Pb Islands Grown on SrTiO$_{3}$ |
| Yonghao Yuan1,2, Xintong Wang1,2, Canli Song1,2, Lili Wang1,2, Ke He1,2, Xucun Ma1,2, Hong Yao1,2,3, Wei Li1,2**, Qi-Kun Xue1,2,4** |
1State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084
2Collaborative Innovation Center of Quantum Matter, Beijing 100084
3Institute for Advanced Study, Tsinghua University, Beijing 100084
4Beijing Academy of Quantum Information Sciences, Beijing 100193
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| Cite this article: |
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Yonghao Yuan, Xintong Wang, Canli Song et al 2020 Chin. Phys. Lett. 37 017402 |
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Abstract We report high-resolution scanning tunneling microscopy (STM) study of nano-sized Pb islands grown on SrTiO$_{3}$, where three distinct types of gaps with different energy scales are revealed. At low temperature, we find that the superconducting gap (${\it\Delta}_{\rm s}$) in nano-sized Pb islands is significantly enhanced from the one in bulk Pb, while there is no essential change in superconducting transition temperature $T_{\rm c}$, giving rise to a larger BCS ratio 2${\it\Delta}_{\rm s}/k_{_{\rm B}}T_{\rm c} \sim 8.31$ and implying stronger electron-phonon coupling. The stronger coupling can originate from the interface electron-phonon interactions between Pb islands and SrTiO$_{3}$. As the superconducting gap is totally suppressed under applied magnetic field, the Coulomb gap with apparent V-shape emerges. Moreover, the size of Coulomb gap (${\it\Delta}_{\rm C}$) depends on the lateral size of Pb islands ($R$) with ${\it\Delta}_{\rm C}\sim 1/R^{0.35}$, indicating that quantum size effect can significantly influence electronic correlations. Our experimental results shall shed important light on the interplay among superconductivity, quantum size effect and correlations in nano-sized strong-coupling superconductors.
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Received: 10 December 2019
Published: 23 December 2019
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| PACS: |
74.78.-w
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(Superconducting films and low-dimensional structures)
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74.78.Na
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(Mesoscopic and nanoscale systems)
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74.55.+v
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(Tunneling phenomena: single particle tunneling and STM)
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73.22.-f
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(Electronic structure of nanoscale materials and related systems)
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73.23.Hk
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(Coulomb blockade; single-electron tunneling)
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| Fund: Supported by the National Natural Science Foundation under Grant Nos. 11674191 and 11825404, the National Key Program for S&T Research and Development under Grant No. 2016YFA0301002, and the Beijing Advanced Innovation Center for Future Chip (ICFC). W.L. was also supported by Beijing Young Talents Plan. |
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