Giorgos P. Tsironis

Wide-band tuneability, nonlinear transmission, and dynamic multistability in SQUID metamaterials

Superconducting metamaterials comprising rf Superconducting QUantum Interference Devices (SQUIDs) have been recently realized and investigated with respect to their tuneability, permeability, and dynamic multistability properties. These properties are a consequence of intrinsic nonlinearities due to the sensitivity of the superconducting state to external stimuli. SQUIDs, made of a superconducting ring interrupted by a Josephson junction, possess yet another source of nonlinearity, which makes them widely tuneable with an applied dc dlux. A model SQUID metamaterial, based on electric equivalent circuits, is used in the weak coupling approximation to demonstrate the dc flux tuneability, dynamic multistability, and nonlinear transmission in SQUID metamaterials comprising non-hysteretic SQUIDs. The model equations reproduce the experimentally observed tuneability patterns and predict tuneability with the power of an applied ac magnetic field. Moreover, the results indicate the opening of nonlinear frequency bands for energy transmission through SQUID metamaterials, for sufficiently strong ac fields.

{\mathcal {PT}}-symmetric dimers with time-periodic gain/loss function

Abstract

Nonreciprocal scattering by PT-symmetric stack of the layers

{\mathcal {PT}}

Resonant combinatorial frequency generation in non-Hermitian hyperbolic metamaterials

PT-symmetric dimers with a time-periodic gain/loss function in a balanced configuration where the amount of gain equals that of loss are investigated analytically and numerically. Two prototypical dimers in the linear regime are investigated: a system of coupled classical oscillators, and a Schrödinger dimer representing the coupling of field amplitudes, each system representing a wide class of physical models. Through a thorough analysis of their stability behavior, we find that turning on the coupling parameter in the classical dimer system leads initially to decreased stability but then to re-entrant transitions from the exact to the broken

\mathcal{PT}-symmetric nonlinear metamaterials and zero-dimensional systems

{\mathcal {PT}}

Wave scattering by PT-symmetric epsilon-near-zero periodic structures

PT-phase and vice versa, as it is increased beyond a critical value. On the other hand, the Schrödinger dimer behaves more like a single oscillator with time-periodic gain/loss. In addition, we are able to identify the conditions under which the behavior of the two dimer systems coincides and/or reduces to that of a single oscillator.