Abstract
Abstract Exceptional points (EPs), also known as non-Hermitian degeneracies, have been observed in parity-time symmetric metasurfaces as parity-time symmetry breaking points. However, the parity-time symmetry condition puts constraints on the metasurface parameter space, excluding the full examination of unique properties that stem from an EP. Here, we thus design a general non-Hermitian metasurface with a unit cell containing two orthogonally oriented split-ring resonators (SRRs) with overlapping resonance but different scattering rates and radiation efficiencies. Such a design grants us full access to the parameter space around the EP. The parameter space around the EP is first examined by varying the incident radiation frequency and coupling between SRRs. We further demonstrate that the EP is also observable by varying the incident radiation frequency along with the incident angle. Through both methods, we validate the existence of an EP by observing unique level crossing behavior, eigenstate swapping under encirclement, and asymmetric transmission of circularly polarized light.
Highlights
When studying the physics of closed systems in which the conservation of energy is strictly obeyed, Hamiltonians are assumed to be Hermitian due to the many appropriate mathematical constraints it puts on the system, such as realness of eigenvalues, existence of an orthonormal basis, and unitary time evolution
Based on the ease and independence with which they can be controlled, parameters ω and Gxy are chosen. ω is directly controlled through incident radiation and Gxy is controlled by changing the distance between split-ring resonators (SRRs) in the unit cell [9, 10]
We have designed a non-Hermitian metasurface composed of orthogonally oriented SRRs to observe an Exceptional points (EPs)
Summary
When studying the physics of closed systems in which the conservation of energy is strictly obeyed, Hamiltonians are assumed to be Hermitian due to the many appropriate mathematical constraints it puts on the system, such as realness of eigenvalues, existence of an orthonormal basis, and unitary time evolution. Many systems in physics are, conveniently described by open systems, which may either gain or lose energy through interactions with its environment, resulting in complex eigenenergies. Such open systems are represented by nonHermitian Hamiltonians. The significance of EPs has frequently been noted in non-Hermitian systems with special constraint of being parity-time symmetric. In these parity-time symmetric systems, the EP is shown to be the point of the parity-time symmetry breaking transition [5,6,7,8,9,10,11,12]. The complex parameter space forms a self-intersecting Riemann sheet
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