Colossal terahertz emission with ultrafast tunability based on van der Waals ferroelectric NbOI$_2$

TL;DR

This paper reports a van der Waals ferroelectric NbOI$_2$ that exhibits colossal, highly efficient, and tunable terahertz emission, advancing ultrafast THz source technology for various applications.

Contribution

It introduces NbOI$_2$ as a new, highly efficient THz emitter with ultrafast tunability, surpassing traditional materials like ZnTe, and explores its generation mechanisms and coherent control.

Findings

THz emission efficiency is an order of magnitude higher than ZnTe.

Demonstrated ultrafast coherent amplification and annihilation of THz emission.

Uncovered the role of ferroelectric polarization in THz generation mechanisms.

Abstract

Terahertz (THz) technology is critical for quantum material physics, biomedical imaging, ultrafast electronics, and next-generation wireless communications. However, standing in the way of widespread applications is the scarcity of efficient ultrafast THz sources with on-demand fast modulation and easy on-chip integration capability. Here we report the discovery of colossal THz emission from a van der Waals (vdW) ferroelectric semiconductor NbOI$_2$. Using THz emission spectroscopy, we observe a THz generation efficiency an order of magnitude higher than that of ZnTe, a standard nonlinear crystal for ultrafast THz generation. We further uncover the underlying generation mechanisms associated with its large ferroelectric polarization by studying the THz emission dependence on excitation wavelength, incident polarization and fluence. Moreover, we demonstrate the ultrafast coherent amplification and annihilation of the THz emission and associated coherent phonon oscillations by employing a double-pump scheme. These findings combined with first-principles calculations, inform new understanding of the THz light-matter interaction in emergent vdW ferroelectrics and pave the way to develop high-performance THz devices on them for quantum materials sensing and ultrafast electronics.