SrTiO3上Pb岛的电子关联库仑能隙和超导能隙的扩大
Coulomb gap induced by electronic correlation and enlarged superconducting gap in laterally confined Pb islands grown on SrTiO3
摘要：
我们报告的高分辨率扫描隧道显微镜（STM）研究纳米尺寸的Pb岛生长在SrTiO 3，其中三种不同类型的间隙具有不同的能量尺度被揭示。低温时，超导能隙（Δs）增大，而超导转变温度（Tc）没有提高，BCS比增大2Δs/kBTc ~ 6.22。这里的强耦合可能源于金属-氧化物界面上的电子-声子耦合。当超导能隙在外加磁场或高温下被抑制时，分别出现库仑能隙和赝能隙。库仑能隙对Pb岛的横向尺寸敏感，表明量子尺寸效应能够影响电子关联，而这在低维超导中通常被忽略。我们的实验结果将对纳米超导体中量子尺寸效应和关联之间的相互作用提供重要的启示。
英文摘要：
We report high-resolution scanning tunneling microscopy (STM) study of nano-sized Pb islands grown on SrTiO3, where three distinct types of gaps with different energy scales are revealed. At low temperature, an enlarged superconducting gap (Δs) emerges while there is no enhancement in superconducting transition temperature (Tc), giving rise to a larger BCS ratio 2Δs/kBTc ~ 6.22. The strong coupling here may originate from the electron-phonon coupling on the metal-oxide interface. As the superconducting gap is suppressed under applied magnetic field or at elevated temperature, Coulomb gap and pseudogap appear, respectively. The Coulomb gap is sensitive to the lateral size of Pb islands, indicating that quantum size effect is able to influence electronic correlation, which is usually ignored in low-dimensional superconductivity. Our experimental results shall shed important light on the interplay between quantum size effect and correlations in nano-sized superconductors.
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