Design and analysis of graphene- and germanium-based plasmonic probe with photonic spin Hall effect in THz frequency region for magnetic field and refractive index sensing

In this work, we analyze the design of a graphene- and germanium-based plasmonic sensor with photonic spin Hall effect (PSHE) for detection of refractive index (RI) of a gas medium and magnetic field (B) applied to the graphene monolayer in THz frequency region. The PSHE phenomenon is studied in both conventional as well as modified weak measurements. The effect of gaseous medium thickness (d(4)), transverse magnetic (TM) mode’s order, and amplified angle parameter (Δ) is studied on the sensor’s performance. Parameters such as sensitivity, resolution, and figure of merit have been considered for sensor’s performance evaluation. The results indicate that in the conventional weak measurements, for a TM(1) mode (with d(4) = 20 µm, B = 0, and Δ = 0.1°), an RI resolution of 2.32 × 10(−12) RIU is achievable for gas medium in the range 1–1.1 RIU. In the modified weak measurements, for a TM(3) mode (with d(4) = 100 µm, B = 0, and Δ = 0.1°), the RI resolution close to 1.39 × 10(−10) RIU is achievable for gas sensing. The same sensor design was also studied for magnetic field sensing while keeping the value of gaseous medium RI (n(4)) as 1. The results indicate that for a TM(1) mode (with d(4) = 20 µm and Δ = 0.1°), in the conventional weak measurements, a magnetic field resolution of 5.31 × 10(−4) µT (i.e., 0.53 nT) is achievable for a range 0–1 T of B. Further, it is found that in contrast with the conventional case, the resolutions in the modified weak measurements are improved for large values of the Δ. Some of the results emerge better or comparable with the resolutions of RI and magnetic field measurement (5 × 10(−9) RIU and 0.7 µT or 1.22 × 10(−11) RIU and 1.46 × 10(−2) µT) existing in the literature.