Tunable On‐Chip Terahertz Isolator Based on Nonreciprocal Transverse Edge Spin State of Asymmetric Magneto‐Plasmonic Waveguide

Abstract Terahertz (THz) isolators are crucial to one‐way transmission in THz application systems. However, it is still challenging to implement THz isolators with integrated structure and tunable characteristics. Herein, a THz isolator based on a magneto‐plasmonic waveguide (MPWG) has been demonstrated. In this InSb‐air‐metal asymmetric waveguide, the plasmonic band gap is excited and thermally tuned by surface plasmons. Moreover, under weak external magnetic fields (EMFs), magneto‐plasmons excite nonreciprocal transverse edge spin states, which break the time‐reversal symmetry of the MPWG and lead to a pair of isolation bandgaps that only allow one‐way transmission. The experimental results of both broadband time‐domain spectrum system and single‐frequency system confirm this isolator can achieve more than 20 dB isolation and only 4 dB insertion loss. More importantly, its isolation can be actively modulated by EMFs from 0 to 0.23 T, and also realize broadband tuning of over 1 THz frequency range by controlling the temperature from 80 to 280 K. This topological edge band structure of transverse spin states and its active manipulation mechanism are helpful to deepen the understanding of nonreciprocal plasmon propagation, and this broadband tunable THz on‐chip isolator is significant to urgently apply in strong THz sources and ultra‐sensitive detectors.