February 2011
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Day February 11, 2011

Armchair graphene nanoribbons: PT-symmetry breaking and exceptional points without dissipation

Maurizio Fagotti, Claudio Bonati, Demetrio Logoteta, Paolo Marconcini, Massimo Macucci

We consider a single layer graphene nanoribbon with armchair edges in a longitudinally constant external potential and point out that its transport properties can be described by means of an effective non-Hermitian Hamiltonian. We show that this system has some features typical of dissipative systems, namely the presence of exceptional points and of PT-symmetry breaking, although it is not dissipative.

Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)

PT-Symmetric Oligomers: Analytical Solutions, Linear Stability and Nonlinear Dynamics

K. Li, P.G. Kevrekidis

In the present work we focus on the case of (few-site) configurations respecting the PT-symmetry. We examine the case of such “oligomers” with not only 2-sites, as in earlier works, but also the cases of 3- and 4-sites. While in the former case of recent experimental interest, the picture of existing stationary solutions and their stability is fairly straightforward, the latter cases reveal a considerable additional complexity of solutions, including ones that exist past the linear PT-breaking point in the case of the trimer, and more complex, even asymmetric solutions in the case of the quadrimer with nontrivial spectral and dynamical properties. Both the linear stability and the nonlinear dynamical properties of the obtained solutions are discussed.

Pattern Formation and Solitons (nlin.PS); Quantum Gases (cond-mat.quant-gas)

PT-symmetry breaking and laser-absorber modes in optical scattering systems

Y. D. Chong, Li Ge, A. Douglas Stone

Using a scattering matrix formalism, we derive the general scattering properties of optical structures that are symmetric under a combination of parity and time-reversal (PT). We demonstrate the existence of a transition beween PT-symmetric scattering eigenstates, which are norm-preserving, and symmetry-broken pairs of eigenstates exhibiting net amplification and loss. The system proposed by Longhi, which can act simultaneously as a laser and coherent perfect absorber, occurs at discrete points in the broken symmetry phase, when a pole and zero of the S-matrix coincide.

Optics (physics.optics); Quantum Physics (quant-ph)