Terahertz Emission in Quantum Materials

Abstract

The study of the interaction between terahertz (THz) radiation and quantum materials has been an active area of research due to its potential for understanding fundamental physics and the development of novel technologies. In this review, we focus on the time-dependent photocurrents, behind which are the up-to-date understanding of the physical processes. We provide the recent advancements in revealing the unique properties of quantum materials via the THz emission spectroscopy. Because the theoretical interpretation of some new experimental results is still evolving, this review is intended to inspire further research in this exciting and rapidly growing field.

Comprehensive study of the ultrafast photoexcited carrier dynamics in Sb2Te3–GeTe superlattices

“…Moreover, the wavevector independent THz emission confirms that the photon drag effect would not be the dominant mechanism for the THz emission in the Sb 2 Te 3 -GeTe superlattices. [37] Owing to the MBE-grown Sb 2 Te 3 -GeTe superlattices, 074210-3 such layered stacking is lacking the space-inversion symmetry. The optical transitions induced by linearly polarized laser pulse give rise to a photocurrent in materials with low spatial symmetry.…”

“…the THz radiation can be fitted well by cos 2β , which is consist with the shift current mechanism. [37,39] different processes, which can be fitted by the phenomenological expression [45,[48][49][50] E THz,x (α,t)…”

“…We also observe the shift current generated by the linear photo-galvanic effect (LPGE) and the injection current generated by the circular photo-galvanic effect (CPGE) in Sb 2 Te 3 -GeTe superlattices, which depend on the topological state with spin-momentum locking. [37][38][39] It can be found that, by decreasing the thickness of GeTe and Sb 2 Te 3 layers, and increasing the number of GeTe and Sb 2 Te 3 layers, the interlayer coupling can be enhanced, which significantly reduces the CPGE contribution. Further, utilizing transient reflectance spectroscopy, a photoinduced bleaching is observed at the wavelength of ∼ 1100 nm to ∼ 1400 nm, demonstrating a bandgap at ∼ 1.0 eV above the Fermi level.…”