Thresholdless characterization in space and time reflection symmetry electronic dimers

We develop a general mutual inductive M, inductive L, and capacitive C couplings parity time symmetry (MLCPTS) electronic dimer model. We successfully show that the dimers separately coupled with M, L, or ML can be made thresholdless by adding a capacitance C in parallel. Thus, sufficient conditions for thresholdless transitions were determined. The scattering properties of our model reveal the suppression of unidirectional invisibility from the gain input when the Hermitian line coupling exceeds a critical point. Likewise, the scattering system becomes unidirectional PTS. Remarkably, under the thresholdless conditions, lasing modes appear for imaginary values of wavenumbers corresponding to either real or purely imaginary values of the gain/loss modulation. This latter demonstrates the ability to control prohibited waves in the linear regime. (C) 2017 Optical Society of America