A tunable graphene-based phase-jump inversion plasmonic sensor for ultra-sensitive refractive index sensing over THz frequency

The surface plasmon resonance effect has been previously reported as an essential mechanism for terahertz wave sensing applications. However, due to its structural geometric parameters dependence, either the reconfiguration of the arrays or the realignment of the prism system is required, which always remains one of the challenges limiting practical applications. Here, a graphene-based phase-jump inversion plasmonic sensor (GPPS) operating at a fixed gap and incident angle is established. The optimal wave vector matching between specific analytes and the GPPS can be achieved by adjusting the Fermi level of graphene. On this basis, an ultrahigh sensitivity of 0.488 THz/RIU is achieved under the optimal Fermi level. Remarkably, the comparison between the phase spectra and the reflective amplitude spectra indicates that the phase-based FoM and Q-factor are two orders of magnitude larger than those calculated by amplitude spectra, which could reach 244RIU-1 and 218.5. The unique phase-jump responses on graphene surface plasmon resonance provide new ideas for ultra-sensitivity THz sensing methods.