Direct imaging of the generalized Brillouin zone in boundary-reconfigurable non-Hermitian electric circuits

초록

Complex-valued eigenvalues and the concomitant non-conservation of state norms underlie characteristic phenomena of non-Hermitian systems, such as dissipation and localization. Recent advances have shown that the band structures are highly sensitive to boundary conditions and are best described by the generalized Brillouin zone (GBZ), a continuous manifold in complex-momentum space. However, active control of the GBZ and its underlying topology remains largely unexplored. Here, we demonstrate controllable manipulation of the GBZ by adjusting the boundary Hamiltonian, leveraging boundary sensitivity. Our measurements show that the GBZ splits into multiple distinct manifolds that simultaneously host both decaying and amplifying eigenmodes, in sharp contrast to the non-Hermitian skin effect under conventional open boundary conditions. By continuously deforming these manifolds, we drive a boundary-controlled topological phase transition that occurs at an exceptional point rather than through a conventional bulk-gap closing. These transitions are dictated by the boundary, not by the bulk, highlighting the exceptional boundary sensitivity of non-Hermitian lattices.

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