Actively tuning optical transmission through hybrid metasurfaces incorporated with multifunctional active media holds great promise for the next generation optical devices. In the terahertz (THz) range, they remain rare due to the lack of dynamic and multifunctional designs and materials. Here, a vanadium dioxide (VO2)‐based hybrid metasurface is proposed to present multifunctional control of THz waves via electrically triggering and ultrafast optical excitation. By minimizing the thermal mass of VO2 and optimizing the VO2 patterns within two side gaps of the asymmetric split‐ring resonators, a hybrid metasurface which can tune the THz wave with an absolute modulation depth up to 54% and a figure of merit as high as 138% is hereby presented. The hybrid metasurface achieves a switching time of 2.2 s under the electrically triggering and offers an ultrafast modulation within 30 ps under the femtosecond pulse excitation. More interestingly, owing to the intrinsic hysteresis behavior of VO2, the hybrid metasurface exhibits distinguishing multistate transmission amplitudes with a single electrical input. In short, this study paves the way for robust multifunctionality in electric‐controlled terahertz switching, photonic memory, and ultrafast terahertz optics.

This Letter investigates the electron heat flux instability using the radial models of the magnetic field and plasma parameters in the inner heliosphere. Our results show that both the electron acoustic wave and the oblique whistler wave are unstable in the regime with large relative drift speed (ΔV e ) between electron beam and core populations. Landau-resonant interactions of electron acoustic waves increase the electron parallel temperature that would lead to suppressing the electron acoustic instability and amplifying the growth of oblique whistler waves. Therefore, we propose that the electron heat flux can effectively drive oblique whistler waves in an anisotropic electron velocity distribution function. This study also finds that lower-hybrid waves and oblique Alfvén waves can be triggered in the solar atmosphere, and that the former instability is much stronger than the latter. Moreover, we clarify that the excitation of lower-hybrid waves mainly results from the transit-time interaction of beaming electrons with resonant velocities v ∥ ∼ ω/k ∥, where ω and k ∥ are the wave frequency and parallel wavenumber, respectively. In addition, this study shows that the instability of quasi-parallel whistler waves can dominate the regime with medium ΔV e at the heliocentric distance nearly larger than 10 times of the solar radius.

The wave-particle cyclotron interaction is a basic process in collisionless plasmas, which results in the redistribution of the energy between plasma waves and charged particles. This paper presents an event observation in order to explore the dynamics of charged particles and plasma waves, i.e., mirror, electromagnetic ion cyclotron (EMIC), and whistler waves, in the Earth's magnetosheath. It shows that when ions have a high-speed streaming velocity parallel to the magnetic field, EMIC waves arise. We also find that the frequency distribution of nearly parallel and nearly antiparallel whistler waves depends on the parallel streaming velocity of electrons. Based on the linear kinetic theory and the fitting plasma parameters, we show that the differential flows among ion components can enhance the ion cyclotron anisotropy instability that is even stronger than the mirror instability. The differential electron flows induce an asymmetry of the growth rate of counter-propagating whistler waves in the electron cyclotron anisotropy instability. On the other hand, the low-frequency EMIC and transverse electromagnetic waves modulate the ion pitch angle distribution. Moreover, when charged particles flow across the magnetic field, both low-and high-energy electrons are deeply trapped by mirror waves. These results illustrate new features of the observed plasma waves and charged particles in the Earth's magnetosheath, which could inspire improvement of the wave models therein.