Laser-initiated electron and heat transport in gold-skutterudite CoSb₃  bilayers resolved by pulsed x-ray scattering

Abstract Electron and lattice heat transport have been investigated in bilayer thin films of gold and CoSb 3 after photo-excitation of the nanometric top gold layer through picosecond x-ray scattering in a pump-probe setup. The kinetics of heat transfer are detected by thermal lattice expansion and compared to simulations based on the two-temperature model of coupling of electron and phonon degrees of freedom. The unexpected observation of a larger portion of the deposited heat being detected in the underlying CoSb 3 layer before the topmost gold layer is heated supports the picture of transport of the photo-excited electrons from gold to the underlying layer to be converted into lattice heat. The change of partition of heat between the gold and CoSb 3 layer with laser fluence and wavelength (either exciting intraband transitions or additionally interband transitions) is rooted in the amplitude of electron temperature. Higher electron temperatures result in a longer equilibration time with the lattice and thus a larger proportion of ballistic electron transport across the interface.