Anomalous resonance frequency shift in liquid crystal-loaded THz metamaterials

Babinet complementary patterns of a spectrally tunable metamaterial incorporating a nematic liquid crystal is normally assumed to exhibit the same tuning range. Here we show that for a hybrid, liquid crystal-loaded metamaterial, the sensitivity of its terahertz resonances to the variations of the refractive index differs substantially for the two complementary patterns. This is due to a mismatch between the alignment of the liquid crystal and the direction of the local electric field induced in the metamaterial patterns. Furthermore, and more intriguingly, our experimental data indicate that it is possible to shift the resonance of the positive metamaterial pattern beyond the limit imposed by the alignment mismatch. Our analysis suggests that the observed anomalous frequency shift results from the orientational optical nonlinearity of a nematic liquid crystal.