Abstract-Superconducting pair-breaking under intense sub-gap terahertz radiation

Applied Physics Letters

Jie Tian, Jack Zuber, Sunchao Huang, Chao Zhang

The relation between the ratio of superconducting carriers and energy gap (a), temperature (b), and parameters 
(E/ω)2${(E/\omega )}^2$(c).

https://aip.scitation.org/doi/abs/10.1063/1.5098045

We study the effect of a strong and low frequency (ω < Δ, the superconducting gap) electrical field on a superconducting state. It is found that the superconducting gap decreases with the field intensity and wavelength. The physical mechanism for this dependence is the multiphoton absorption by a superconducting electron. By constructing the state of a superconducting electron dressed by photons, we determined the dependence of the superconducting gap on E/ω$E/\omega$ and temperature. We show that the critical temperature is determined by the parameter E/ω$E/\omega$ which is distinct from that induced by the heating effect. The result is consistent with experimental findings. This result can be applied to study terahertz nonlinear superconducting metamaterials.

Abstract-Strong tunable photomixing in semi-Dirac materials in the terahertz regime

                                                                   

Sunchao Huang, My Hanh Tran, Jack Zuber, Qian Wang, Yiming Zhu, and Chao Zhang

https://www.osapublishing.org/josab/abstract.cfm?uri=josab-36-2-200

We demonstrate a strong and anisotropic photomixing effect in an electronic system whose energy–momentum dispersion is parabolic in the 𝑥$$ direction and linear in the 𝑦$$ direction, such as a TiO2/VO2${}_{\mathrm{}}{}_{\mathrm{}}$ multilayered structure. The third-order photoresponses along the linear and parabolic directions have been analyzed and determined quantitatively. We have found a remarkable tunability of the mixing efficiency along the parabolic direction by a small electric field in the linear direction, up to two orders of magnitude. In the terahertz (THz) regime, the third-order response is comparable to the linear response under an applied field of 103–104  V/cm${\mathrm{}}^{\mathrm{}}{\mathrm{}}^{\mathrm{}}\mathrm{}$. Additionally, the nonlinear response persists at room temperature. The results may have applications where different current responses are required along different directions in the THz regime.

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