Experimental evidence of dominant ultrafast diffusive energy transport by hot electrons in Cu
Abstract
When the dimensions of structures shrink to the order of the inelastic mean free path of the energy-carrying quasi-particles, the character of energy transport changes from diffusive to ballistic. However, the point of transition remains a matter of debate. Here, we leverage the fluence-dependent transport efficiency to distinguish ballistic and diffusive electron transport in an approach not relying on the transport velocity. We follow the energy that is rapidly transferred across Cu layers of different thicknesses via hot electrons from a photo-excited Pt layer into a buried Ni detection layer. In the Ni layer, the transported energy linearly relates to a rapid lattice expansion, which we probe via ultrafast x-ray diffraction. A nonlinear dependence of the Ni strain amplitude on the absorbed laser fluence indicates that the transport through Cu becomes more efficient with increasing fluence, which is inconsistent with a ballistic scenario but reproduced by a diffusive energy transport model. We already identify that for a Cu thickness of about 50 nm, i.e., about twice the electronic inelastic mean free path, diffusive electronic energy transport dominates the spatial energy distribution. Our experimental approach is generally applicable to distinguish diffusion from ballistic energy transport.
Article Details
Journal Info
Applied Physics Letters
American Institute of Physics
Authors (18)
J. Jarecki
Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie 1 , 12489 Berlin,
L. Mehner
Institut für Physik und Astronomie, Universität Potsdam 2 , 14476 Potsdam,
M. Mattern
Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie 1 , 12489 Berlin,
A. Jurgilaitis
MAX IV Laboratory, Lund University 3 , P.O. Box 118, 221 00 Lund,
S. P. Zeuschner
Institut für Physik und Astronomie, Universität Potsdam 2 , 14476 Potsdam,
B. Ahn
MAX IV Laboratory, Lund University 3 , P.O. Box 118, 221 00 Lund,
F. Baltrusch
Institut für Physik und Astronomie, Universität Potsdam 2 , 14476 Potsdam,
J. C. Ekström
MAX IV Laboratory, Lund University 3 , P.O. Box 118, 221 00 Lund,
D. Kroon
MAX IV Laboratory, Lund University 3 , P.O. Box 118, 221 00 Lund,
M. Herzog
Institut für Physik und Astronomie, Universität Potsdam 2 , 14476 Potsdam,
C. Walz
Institut für Physik und Astronomie, Universität Potsdam 2 , 14476 Potsdam,
F.-C. Weber
Institut für Physik und Astronomie, Universität Potsdam 2 , 14476 Potsdam,
J. Larsson
MAX IV Laboratory, Lund University 3 , P.O. Box 118, 221 00 Lund,
M. Hehn
Institut Jean Lamour (UMR CNRS 7198), Université Lorraine 7 , 54000 Nancy,
J.-E. Pudell
European X-ray Free-Electron Laser Facility 8 , 22869 Schenefeld,
D. Schick
Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie 1 , 12489 Berlin,
A. von Reppert
Institut für Physik und Astronomie, Universität Potsdam 2 , 14476 Potsdam,
M. Bargheer
Institut für Physik und Astronomie, Universität Potsdam 2 , 14476 Potsdam,