Fig. 1: Corner and edge modes activated by parity-time (\({{{{{{{\mathcal{PT}}}}}}}}\)) symmetry breaking.
From: Activating non-Hermitian skin modes by parity-time symmetry breaking
a, b The spectrum under open boundary conditions (OBCs) (gray) of Hγ,2D with fixed ky can be a complex or b real depending on whether \({{{{{{{\mathcal{PT}}}}}}}}\) symmetry is restored by the non-Hermitian skin effect. For reference, the spectrum under periodic boundary conditions (PBCs) (brown) is always complex. c Full spectrum of Hγ,2D as a 2D model, with PBCs along the y direction. Pink and blue cross sections correspond to the spectra in a and b (also indicated by gray arrows). The full x, y-OBC spectrum (colored according to the fractal dimension FD) is contained within the set of y-PBC eigenenergies, as shown by the lower part of the panel (gray). Corner modes with their fractal dimension FD ≈ 0 (I,II, triangles) are plotted in d, and exist at Im(E) ≠ 0 where \({{{{{{{\mathcal{PT}}}}}}}}\) symmetry is broken. An edge mode with FD ≈ 1 (III, square) exists at Im(E) = 0, as plotted in e. Parameters are γ = 1.4, t1 = 0.1, t2 = 0.1, v = 1, and u = 0.7.
