Engineering ultra-strong electron-phonon coupling and nonclassical electron transport in crystalline gold with...

Electrical resistivity in good metals, particularly noble metals such as gold (Au), silver (Ag), or copper, increases linearly with temperature (T) for T > Θ_D, where Θ_D is the Debye temperature. This is because the coupling (λ) between the electrons and the lattice vibrations, or phonons, in these metals is weak, with λ ~ 0.1-0.2. In this work, we outline a nanostructuring strategy of crystalline Au where this concept of metallic transport breaks down. We show that by embedding a distributed network of ultra-small Ag nanoparticles (AgNPs) of radius ~ 1-2 nm inside a crystalline Au shell, the electron-phonon interaction can be enhanced, with an effective λ as high as  ≈ 20. With increasing AgNP density, the electrical resistivity deviates from T-linearity and approaches a saturation to the Mott-Ioffe-Regel scale ρ_MIR ~ ha/e² for both disorder (T → 0) and phonon (T ≫ Θ_D)-dependent components of resistivity (here, a = 0.3 nm, is the lattice constant of Au).