Observation of Negative Effective Thermal Diffusion in Gold Films

Alexander Block, Renwen Yu, Ieng Wai Un, Sebin Varghese, Matz Liebel, Niek F. van Hulst, Shanhui Fan, Klaas Jan Tielrooij, Yonatan Sivan

Research output: Contribution to journalArticlepeer-review


Ultrafast light-induced spatiotemporal dynamics in metals in the form of electron and/or phonon heating is a fundamental physical process that has tremendous practical relevance. In particular, understanding the resulting lateral heat transport is of key importance for various (opto)electronic applications and thermal management but has attracted little attention. Here, by using scanning ultrafast thermo-modulation microscopy to track the spatiotemporal electron diffusion in thin gold films, we show that a few picoseconds after the optical pump there is unexpected heat flow from phonons to electrons, accompanied by negative effective thermal diffusion, characterized by shrinking of the spatial region with increased temperature. Peculiarly, this occurs on the intermediate time scale, between the few picosecond long thermalization stage and the many picosecond stage dominated by thermoacoustic vibrations. We accurately reproduced these experimental results by calculating the spatiotemporal photothermal response based on the two-temperature model and an improvement of the standard permittivity model for gold. Our findings facilitate the design of nanoscale thermal management strategies in photonic, optoelectronic, and high-frequency electronic devices.

Original languageAmerican English
JournalACS Photonics
StateAccepted/In press - 1 Jan 2022


  • energy transport
  • heat generation and diffusion
  • high-resolution microscopy
  • permittivity modeling
  • plasmonics

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Biotechnology
  • Atomic and Molecular Physics, and Optics
  • Electrical and Electronic Engineering


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