Fig. 3: Quadrupole topological phases in heat transport induced by non-Hermitian couplings and relevant band structures.
From: Observation of bulk quadrupole in topological heat transport
a illustrates the square-lattice with different coupling strengths and the four-site unit structure. The directions and magnitudes of the imposed advections (green arrows) on each site are same to hold the non-Hermitian properties. The intercell and intracell channels are fabricated to different structures to enable the different thermal coupling strengths. b presents the inner structures of these thermal coupling channels with different coupling strength ratios. c–e indicate the imaginary spectra of the dispersion induced by non-Hermitian couplings respectively at the in-gap corner, gapped edge, and trivial bulk states. The horizontal and vertical axes denote the effective Bloch wave numbers and imaginary value of the eigenvalue. The red and blue dots in c and d respectively indicate the corner and edge states.
