Electromagnetic-field imbalance in surface plasmon polariton and its role in slow propagation and field-matter interaction

We present the results of a theoretic study of the electromagnetic field imbalance in surface plasmon polaritons (SPPs), which reveal that the magnetic field components induced by the electric fields normal and parallel to a metal surface cancel each other in SPPs, resulting in an imbalance. A group velocity analysis shows that this imbalance contributes significantly to the slow propagation of SPPs. We also analyze the enhanced spontaneous emission and nonlinearity in plasmonic cavities, and the results indicate that the electromagnetic field imbalance must be considered to correctly estimate the interaction strength.