Phonon‐Dominated Energy Transport in Purely Metallic Heterostructures

Abstract Ultrafast X‐ray diffraction is used to quantify the transport of energy in laser‐excited nanoscale gold–nickel (Au–Ni) bilayers. Electron and efficient electron–phonon coupling Ni convert laser‐deposited conduction electrons within a few picoseconds into strong non‐equilibrium between hot cold Au phonons at bilayer interface. Modeling subsequent equilibration dynamics various two‐temperature models confirms that for ultrathin films, thermal dominated by instead because weak Au.