The Electronic Interface State characterization of Hyperbolic Metamaterials

The metal/insulator junction is the place where the breakage of translational symmetry in the crystal structure occurs. It contains a large density of partially bonded atoms that can be broken easily by applying a strong electrical stress at the interface. The result is a high concentration of defects at the interfacial layer in the insulator, the so-called interface states which can trap electrons at the interface for a short time, locally lower down the tunneling barrier there, and participate in the conduction and capacitance process in metal-insulator-metal (MIM) structures. A trapped electron shows photoresponse to a light source with a photon energy in the photoresponsive energy band of the structure which commonly is used to characterize the density of interface states and their energy distribution. In this work, we employ interface states to characterize photonic properties of subwavelength structures such as hyperbolic metamaterials made based on MIM junctions. Optical power dependence of interface states' photoresponse is used to characterize the slow-light and field confinement effects of nanoscale metal-dielectric multilayers in their epsilon-near-zero (ENZ) spectral region.