Phys. Rev. B 94, 201103(R) (2016)

The coexistence of two energy levels and eigenstates to form so-called exceptional points (EPs) has been predicted and demonstrated in various physical systems including 2D microwave cavities and coupled atom–cavity systems. However, EPs in 3D plasmonic systems are elusive so far. Ashok Kodigala, Thomas Lepetit and Boubacar Kanté at the University of California San Diego, USA, have now theoretically shown that EPs can occur in 3D systems of coupled plasmonic nanoresonators. This is achieved by tailoring suitable near-field and far-field interactions to yield the required field distributions. The specific 3D system studied consists of three rectangular bars of gold with carefully designed dimensions so that they are resonant at an excitation vacuum wavelength of 1.55 μm (that is, frequency of 193.5 THz). The bars are placed close together and their relative positions adjusted, and the resultant mode coupling analysed by a non-Hermitian effective Hamiltonian approach. The theoretical results show that appropriate placement of the bars resulted in mode symmetry enabling an EP at a frequency of ∼212 THz.