Deviations in Thermal Conductivity Challenge Wiedemann-Franz Law

Researchers at the University of Virginia have presented new findings that cast doubt on the validity of the Wiedemann-Franz law, a long-established correlation between heat and charge transport in metals. By conducting independent measurements on AlCu thin films, the team discovered that the law overpredicts thermal conductivity by at least 10% in all films, indicating modest deviations in predicted thermal conductivity. This research highlights the limitations of the Wiedemann-Franz law in specific contexts, particularly inelastic scattering at room temperature.

Key Takeaways:

• The Wiedemann-Franz law, which correlates heat and charge transport in metals, is challenged by new research on AlCu thin films.
• Independent measurements of in-plane thermal and electrical conductivities across four AlCu films (thicknesses: 174, 98, 53, and 24 nm) reveal deviations in predicted thermal conductivity, with the law overpredicting it by at least 10% in all films.
• The team utilized time-domain thermoreflectance, beam-offset configurations, and the time-resolved magneto-optic Kerr effect to measure in-plane thermal conductivity, while four-point probe techniques were used for electrical conductivity measurements.
• Infrared variable angle spectroscopic ellipsometry demonstrated increased electron scattering rates in the thinnest film (h ≈ 24 nm), indicating electron-boundary scattering drives the reduction in in-plane thermal conductivity.
• This research supports the notion that the Wiedemann-Franz law is generally an elastic scattering process, which is supported by thermal conductivity measurements and analysis.

Statistics:

• The Wiedemann-Franz law overpredicts thermal conductivity by at least 10% in all AlCu films.
• The team conducted measurements on four AlCu films with thicknesses of 174, 98, 53, and 24 nm.
• The thinnest film (h ≈ 24 nm) showed an increased electron scattering rate, as demonstrated by infrared variable angle spectroscopic ellipsometry.
• The research has been peer-reviewed and published in the journal Applied Physics Letters.

Sources:

• NewsRx LLC, Investigators at University of Virginia Discuss Findings in Applied Physics (In-plane Thermal Conductivity and the Applicability of the Wiedemann-franz Law In Dilute Alcu Thin Films)
• Applied Physics Letters, "In-plane Thermal Conductivity and the Applicability of the Wiedemann-franz Law In Dilute Alcu Thin Films" by P.E. Hopkins et al., 2025; 127(11)
• Aip Publishing, Journal of Physics Research, "Investigators at University of Virginia Discuss Findings in Applied Physics (In-plane Thermal Conductivity and the Applicability of the Wiedemann-franz Law In Dilute Alcu Thin Films)", October 21, 2025; p 218.