Surface Superconductivity with High Transition Temperatures in Layered Ca<sub><i>n</i></sub>B<sub><i>n</i>+1</sub>C<sub><i>n</i>+1</sub> Films.
basic_science · Level V
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- Record sourced from PubMed, PMID 36790290.
- Also identified by DOI 10.1021/acs.nanolett.2c05038.
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Abstract
Proposed by Ginzberg nearly 60 years ago, surface superconductivity refers to the emergent phenomenon that the electrons on or near the surface of a material becomes superconducting despite its bulk is nonsuperconducting. Here, based on first-principles calculations within density functional theory, we predict that the superconducting transition temperature <i>T</i><sub>c</sub> at the surfaces of Ca<sub><i>n</i></sub>B<sub><i>n</i>+1</sub>C<sub><i>n</i>+1</sub> (<i>n</i> = 1, 2, 3, ...) films can be drastically enhanced to ∼90 K from 8 K for bulk CaBC. Our detailed analyses reveal that structural symmetry reduction at surfaces induces pronounced carrier self-doping into the surface B-C layer of the films and shifts the σ-bonding states toward the Fermi level; furthermore, the in-plane stretching modes of the surface layers experience significant softening. These two effects work collaboratively to strongly enhance the electron-phonon coupling, which in turn results in much higher <i>T</i><sub>c</sub> values than the McMillian limit. These findings point to new material platforms for realizing unusually high-<i>T</i><sub>c</sub> surface superconductivity.