Reconfigurable exceptional points for enhanced sensitivity in a high-Q toroidal spoof localized surface plasmonic...

Exceptional points (EPs) occur in non-Hermitian systems when two or more eigenstates coalesce, resulting in degenerate eigenvalues and distinctive physical phenomena that deviate significantly from conventional frameworks. Such singularities have attracted extensive research interest due to their potential in asymmetric mode switching, nonreciprocal transmission, and ultrasensitive sensing applications. Nonetheless, the practical implementation of EP-based sensors faces challenges arising from inherent fabrication imperfections, causing deviations from ideal EP conditions in rigid structural designs. Moreover, weak field coupling often limits the ability to detect exceedingly subtle perturbations. In this Letter, we introduce a reconfigurable EP sensor employing a high quality-factor (Q-factor) toroidal spoof localized surface plasmonic resonator (TSLSPR) with a suspended configuration, enhancing the reconfigurability of EP states across multipolar plasmonic modes. By strategically positioning two dielectric scatterers, our proposed EP sensor demonstrates significantly amplified frequency splitting compared to conventional diabolic point (DP) sensors, achieving an exceptionally low detection limit of 0.0001λ (diameter of 0.01 mm) and a notably high Q-factor of up to 423. This work presents an innovative approach for advancing high-sensitivity detection technologies and may stimulate further research into novel EP-based photonic devices.