$\mathcal{PT}$-symmetry breaking in a Kitaev chain with one pair of gain-loss potentials

• URL: http://arxiv.org/abs/2103.07058v1
• Date: Fri, 12 Mar 2021 03:10:45 GMT
• Title: $\mathcal{PT}$-symmetry breaking in a Kitaev chain with one pair of gain-loss potentials
• Authors: Kaustubh S. Agarwal and Yogesh N. Joglekar
• Abstract summary: Parity-time symmetric systems are governed by non-Hermitian Hamiltonians with exceptional-point (EP) degeneracies. Here, we obtain the $mathcalPT$-threshold for a one-dimensional, finite Kitaev chain. In particular, for an even chain with zero on-site potential, we find a re-entrant $mathcalPT$-symmetric phase bounded by second-order EP contours.
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• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Parity-time ($\mathcal{PT}$) symmetric systems are classical, gain-loss systems whose dynamics are governed by non-Hermitian Hamiltonians with exceptional-point (EP) degeneracies. The eigenvalues of a $\mathcal{PT}$-symmetric Hamiltonian change from real to complex conjugates at a critical value of gain-loss strength that is called the $\mathcal{PT}$ breaking threshold. Here, we obtain the $\mathcal{PT}$-threshold for a one-dimensional, finite Kitaev chain -- a prototype for a p-wave superconductor -- in the presence of a single pair of gain and loss potentials as a function of the superconducting order parameter, on-site potential, and the distance between the gain and loss sites. In addition to a robust, non-local threshold, we find a rich phase diagram for the threshold that can be qualitatively understood in terms of the band-structure of the Hermitian Kitaev mo del. In particular, for an even chain with zero on-site potential, we find a re-entrant $\mathcal{PT}$-symmetric phase bounded by second-order EP contours. Our numerical results are supplemented by analytical calculations for small system sizes.

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