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Correlating Electron–Phonon Coupling and In Situ High-Temperature Atomic-Scale Surface Structure at the Metallic Nb(100) Surface by Helium Atom Scattering and Density Functional Theory

Research Theme

Beam Acceleration
Published April 9, 2024

Helium atoms scatter from the electron density of metal surfaces. Thus, the electron-phonon coupling (EPC) constant determines the degree to which lattice vibrational dynamics affect the scattered helium’s. This allows one to extract EPC constant (λ) from helium atom scattering.

Caleb J. Thompson, Michael F. Van Duinen, Michelle M. Kelley, Tomás A. Arias, and S. J. Sibener

Electron–phonon coupling (EPC) in Nb is responsible for the formation of its superconducting state. The EPC constant (λ) is a

Helium scattering

dimensionless constant that quantifies the effective strength of electron–phonon interactions in a material. This constant then determines many superconducting properties such as the critical temperature (TC) and superconducting gap. We have utilized helium atom scattering’s unique capability to measure both surface structure and surface EPC (SEPC) constant (λS) to connect atomic-scale surface structure with its effect on λS and thus surface superconductivity.

Helium atom scattering simultaneously measured the surface EPC constant (λS) and atomic-scale surface structure of the

unreconstructed, metallic Nb(100) surface. Density functional theory (DFT) with local averaging agrees well with the HAS data. The Nb(100) surface λS was measured to be 0.50 ± 0.08, which is ∼1/2 the reported bulk Nb λ values. From this λS we estimate significantly diminished superconducting properties, TC and Hsh. This study shows that diminished superconductivity at Nb SRF cavity surfaces may also be due to the interface itself even without oxygen. These results contain the first λ measured for the metallic Nb(100) and any Nb surface. These measurements begin a fundamental understanding of the atomic-scale surface structure’s effect on EPC and superconductivity in Nb.

Reference: Thompson, C. J.; Van Duinen, M. F.; Kelley, M. M.; Arias, T. A.; Sibener, S. J. Correlating Electron–Phonon Coupling and In Situ High-Temperature Atomic-Scale Surface Structure at the Metallic Nb(100) Surface by Helium Atom Scattering and Density Functional Theory. J. Phys. Chem. C 2024. https://doi.org/10.1021/acs.jpcc.4c00852.

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