Anisotropic strain relaxation-induced directional ultrafast carrier dynamics in RuO 2 films
- Seung Gyo Jeong
- In Hyeok Choi
- Seungjun Lee
- Jin Young Oh
- Sreejith Nair
- Jae Hyuck Lee
- Changyoung Kim
- Ambrose Seo
- Woo Seok Choi
- Tony Low
- Jong Seok Lee
- Bharat Jalan
2025-07-25
Ultrafast light-matter interactions inspire potential functionalities in picosecond optoelectronic applications. However, achieving directional carrier dynamics in metals remains challenging due to strong carrier scattering within a multiband environment, typically expected for isotropic carrier relaxation. In this study, we demonstrate epitaxial RuO 2 /TiO 2 (110) heterostructures grown by hybrid molecular beam epitaxy to engineer polarization selectivity of ultrafast light-matter interactions via anisotropic strain engineering. Combining spectroscopic ellipsometry, x-ray absorption spectroscopy, and optical pump-probe spectroscopy, we revealed the strong anisotropic transient optoelectronic response at an excitation energy of 1.58 eV in strain-engineered RuO 2 /TiO 2 (110) heterostructures along both in-plane [001] and [1 1 ¯ 0] crystallographic directions. Theoretical analysis identifies strain-induced modifications in band nesting as the underlying mechanism for enhanced anisotropic carrier relaxation observed at this excitation energy. These findings establish epitaxial strain engineering as a powerful tool for tuning anisotropic optoelectronic responses with near-infrared excitations in metallic systems, paving the way for next-generation polarization-sensitive ultrafast optoelectronic devices.