Experimentally probing non-Hermitian spectral transition and eigenstate skewness

Probing complex-valued spectra and biorthogonal eigenstates in non-Hermitian systems remains experimentally challenging. The authors present here a Green's function based method that directly measures these fundamental quantities in two-dimensional acoustic lattices. By capturing the full response matrix, they demonstrate eigenstate skewness and geometry-dependent spectral transitions. This universal method overcomes the limits of conventional pump\leavevmode\hbox{-}probe or complex\leavevmode\hbox{-}frequency techniques, providing a robust route for exploring exotic non\leavevmode\hbox{-}Hermitian phenomena across wave\leavevmode\hbox{-}based platforms.