Layer-Dependent Superconductivity in Iron-Based Superconductors CsCa<sub>2</sub>Fe<sub>4</sub>As<sub>4</sub>F<sub>2</sub> and CaKFe<sub>4</sub>As<sub>4</sub>.
basic_science · Level V
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- Record sourced from PubMed, PMID 38787786.
- Also identified by DOI 10.1021/acs.nanolett.4c01725.
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Abstract
In the quasi-two-dimensional superconductor NbSe<sub>2</sub>, the superconducting transition temperature (<i>T</i><sub>c</sub>) is layer-dependent, decreasing by about 60% in the monolayer limit. However, for the extremely anisotropic copper-based high-<i>T</i><sub>c</sub> superconductor Bi<sub>2</sub>Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>8+δ</sub> (Bi-2212), the <i>T</i><sub>c</sub> of the monolayer is almost identical with that of its bulk counterpart. To clarify the effect of dimensionality on superconductivity, here, we successfully fabricate ultrathin flakes of iron-based high-<i>T</i><sub>c</sub> superconductors CsCa<sub>2</sub>Fe<sub>4</sub>As<sub>4</sub>F<sub>2</sub> and CaKFe<sub>4</sub>As<sub>4</sub>. It is found that the <i>T</i><sub>c</sub> of monolayer CsCa<sub>2</sub>Fe<sub>4</sub>As<sub>4</sub>F<sub>2</sub> (after tuning to the optimal doping by ionic liquid gating) is about 20% lower than that of the bulk crystal, while the <i>T</i><sub>c</sub> of three-layer CaKFe<sub>4</sub>As<sub>4</sub> decreases by 46%, showing a more pronounced dimensional effect than that of CsCa<sub>2</sub>Fe<sub>4</sub>As<sub>4</sub>F<sub>2</sub>. By carefully examining their anisotropy and the <i>c</i>-axis coherence length, we reveal the general trend and empirical law of the layer-dependent superconductivity in these quasi-two-dimensional superconductors.