Nonlinear dynamic manipulation of terahertz waves by superconductor-metal hybrid metasurfaces

• Applicant: Dr. Siyu Duan
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 557566396

Although superconducting materials have been found to exhibit remarkable nonlinear effects in the terahertz (THz) band of electromagnetic waves, experimentally it is not straightforward to generate the required extremely strong THz electric field and the understanding of the nonlinear responses is far from being established. The application of these nonlinear effects has great potential for fabricating THz devices which remains to be explored. In this project, I will use a novel approach of superconductor-metal hybrid metasurfaces to achieve nonlinear and ultrafast dynamic manipulation of terahertz waves. In particular, I will leverage the Higgs mode or Josephson plasmon mode of superconductors by using superconductor-metal hybrid metasurfaces to explore new physical phenomena and to develop THz functional devices. Based on my previous research experience on metasurfaces and superconductors, I will design and fabricate two types of hybrid metasurfaces for developing tunable THz sources and ultrafast THz modulators, respectively. I aim to observe new nonlinear physical phenomena using these hybrid metasurfaces. One is high-order harmonic generation in the non-perturbative regime of s-wave and d-wave superconductors. The other is the nonlinear coupling between the Higgs mode and Josephson plasmon mode in the d-wave superconductor. These nonlinear responses will be studied by building up time-resolved terahertz spectroscopy using a femtosecond laser system and combining it with tunable cryogenic conditions. The proposed studies on the excitation and modulation of the Higgs mode and the Josephson plasmon resonance will provide new knowledge of THz nonlinearity in superconducting materials which are driven out of thermal equilibrium, and gain fruitful insights into the understanding of superconductivity and nonlinear optical effects. Also, the obtained hybrid metasurfaces can promote the development of THz devices for potential applications.

• DFG Programme: WBP Position