Colossal Intrinsic Phase-Shift in Broad sub-Terahertz Band Enabled by Magnetoelastic Coupling for 6G Communication Technology

Terahertz (THz) radiation spectral band-based 6G communication requires efficient functional devices such as filters, mixers, polarizers, and modulators. Wherein controlling the phase of the THz pulse is crucial for wave-shaping mechanisms, current methods typically rely on sophisticated metamaterials, which offer a limited bandwidth and involve an intricate and expensive approach. Here, we introduce a novel method for achieving an extraordinary intrinsic THz phase shift by leveraging the magnetoelastic mechanism. Using this approach, an intrinsic <i>colossal</i> THz phase-shift of ∼566° at 0.75 THz, with a linear phase-frequency relationship across a broad spectrum of 100-750 GHz, was demonstrated in Ba₃BiRu₂O₉ across the magnetoelastic transition temperature (<i>T</i>*). It outperforms state-of-the-art free-space meta-modulators in the 6G relevant sub-THz frequency band. This THz phase-shift is thermally bistable and scales with the dielectric constant. With the help of theoretical calculations, we attribute this effect to a large modulation of the dielectric phase across <i>T</i>*, which arises from the intricate coupling of phonons with spin excitations. Magnetodielectric behavior across <i>T</i>* facilitates additional control of the THz phase in an applied magnetic field. Based on the findings, we propose a proof-of-concept for a MODEM (modulation and demodulation) system for THz communications, utilizing the linear-THz phase-frequency relationship of Ba₃BiRu₂O₉ in sub-THz band.