Terahertz interface states in a heterostructure parallel plate waveguide

Heterojunction is usually regarded as an interface structure composed of two semiconductor materials with the different band structures. Some unusual interface effects, such as band bending, charge accumulation or depletion, will occur at the interface, which is completely different from the electrical and optical properties of a single material. Here, we report our experimental observation and theoretical and numerical validation of a terahertz (THz) interface state in a heterostructure corrugated parallel plate waveguide, which is seamlessly connected by two periodic corrugated waveguides with similar bandgaps but different structures. The THz interface state that we observed occurs at the connection of the two waveguides and causes an extraordinary narrow linewidth transmission peak within the original bandgap, whose mechanism is attributed to the local resonance. The center frequency of the transmission peak can be tuned by adjusting the interface length, while its bandwidth narrows with the increased number of periods of corrugated structure. These findings on THz interface states in heterostructure waveguides could be applicable in narrow linewidth filters, high-sensitivity sensors, and detectors.