Control of ultrafast hot electron dynamics in epsilon-near-zero conductive oxide thin films

Sudip Gurung; Subhajit Bej; Quynh Dang; Ambaresh Sahoo; Aleksei Anopchenko; Zhenhuan Yi; Alexei V Sokolov; Andrea Marini; Ho Wai Howard Lee

doi:10.1126/sciadv.adu8850

Control of ultrafast hot electron dynamics in epsilon-near-zero conductive oxide thin films

Sci Adv. 2025 May 23;11(21):eadu8850. doi: 10.1126/sciadv.adu8850. Epub 2025 May 21.

Authors

Sudip Gurung^{1

2}, Subhajit Bej^{2

3}, Quynh Dang^{1

4

5}, Ambaresh Sahoo⁶, Aleksei Anopchenko¹, Zhenhuan Yi², Alexei V Sokolov², Andrea Marini⁶, Ho Wai Howard Lee^{1

2

4

5}

Affiliations

¹ Department of Physics and Astronomy, University of California, Irvine, CA 92697, USA.
² The Institute for Quantum Science and Engineering, Texas AM University, College Station, TX 77843, USA.
³ Photonics Laboratory, Tampere University, FI-33720 Tampere, Finland.
⁴ Beckman Laser Institute and Medical Clinic, University of California, Irvine, CA 92697, USA.
⁵ Eddleman Quantum Institute, University of California, Irvine, CA 92697, USA.
⁶ Department of Physical and Chemical Sciences, University of L'Aquila, Via Vetoio, I-67100 L'Aquila, Italy.

Abstract

The dynamics of nonlinear optical processes in epsilon-near-zero (ENZ) transparent conductive oxides (TCOs) are primarily governed by hot electron relaxation with a sub-picosecond response. However, there is currently a lack of comprehensive understanding of the ultrafast electron dynamics in nonlinear TCO ENZ materials. This study investigates the effects of laser peak power and ENZ mode excitation on hot electron relaxation in TCOs. Our experimental analysis theoretically supported by a hydrodynamic model reveals that increasing laser pulse intensity extends hot electron relaxation time by more than 200%, while ENZ mode excitation increases it by more than 40% in representative TCO ENZ materials. This research demonstrates the controllable modulation of ultrafast ENZ nonlinearity via pulse peak power and ENZ mode field enhancement. These findings provide substantial insights into the potential utilization of ENZ nonlinearity for the development of optical and quantum computing components, including ultrafast optical switches, dynamic pulse shapers, and modulators.