TY  - JOUR
A1  - Pudell, Jan-Etienne
A1  - Maznev, A. A.
A1  - Herzog, Marc
A1  - Kronseder, M.
A1  - Back, Christian H.
A1  - Malinowski, Gregory
A1  - von Reppert, Alexander
A1  - Bargheer, Matias
T1  - Layer specific observation of slow thermal equilibration in ultrathin metallic nanostructures by femtosecond X-ray diffraction
JF  - Nature Communications
N2  - Ultrafast heat transport in nanoscale metal multilayers is of great interest in the context of optically induced demagnetization, remagnetization and switching. If the penetration depth of light exceeds the bilayer thickness, layer-specific information is unavailable from optical probes. Femtosecond diffraction experiments provide unique experimental access to heat transport over single digit nanometer distances. Here, we investigate the structural response and the energy flow in the ultrathin double-layer system: gold on ferromagnetic nickel. Even though the excitation pulse is incident from the Au side, we observe a very rapid heating of the Ni lattice, whereas the Au lattice initially remains cold. The subsequent heat transfer from Ni to the Au lattice is found to be two orders of magnitude slower than predicted by the conventional heat equation and much slower than electron-phonon coupling times in Au. We present a simplified model calculation highlighting the relevant thermophysical quantities.
Y1  - 2018
U6  - https://doi.org/10.1038/s41467-018-05693-5
SN  - 2041-1723
VL  - 9
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Herzog, Marc
A1  - von Reppert, Alexander
A1  - Pudell, Jan-Etienne
A1  - Henkel, Carsten
A1  - Kronseder, Matthias
A1  - Back, Christian H.
A1  - Maznev, Alexei A.
A1  - Bargheer, Matias
T1  - Phonon-dominated energy transport in purely metallic heterostructures
JF  - Advanced functional materials
N2  - Ultrafast X-ray diffraction is used to quantify the transport of energy in laser-excited nanoscale gold-nickel (Au-Ni) bilayers. 
Electron transport and efficient electron-phonon coupling in Ni convert the laser-deposited energy in the conduction electrons within a few picoseconds into a strong non-equilibrium between hot Ni and cold Au phonons at the bilayer interface. 

Modeling of the subsequent equilibration dynamics within various two-temperature models confirms that for ultrathin Au films, the thermal transport is dominated by phonons instead of conduction electrons because of the weak electron-phonon coupling in Au.
KW  - heterostructures
KW  - nanoscale energy transports
KW  - non-equilibrium
KW  - thermal
KW  - transports
KW  - ultrafast phenomena
Y1  - 2022
U6  - https://doi.org/10.1002/adfm.202206179
SN  - 1616-301X
SN  - 1616-3028
VL  - 32
IS  - 41
PB  - Wiley-VCH
CY  - Weinheim
ER  -