Fig. 1: Quadrupole topological phases in heat transport induced by Hermitian advection and relevant band structures.
From: Observation of bulk quadrupole in topological heat transport
a presents a square-lattice consisting of 16 sites in a grid thermal system. The red border indicates a four-site unit-structure. ΩI/II represents the magnitude of the angular velocities imposed on each site. b Schematic unit-structure with four sites, and ax/y presents the widths for heat transport between the centers of neighboring sites. The light-yellow and light-red colors indicate the counter-advections imposed on corresponding sites. The green arrows present the advective directions. Each advection can be decoupled as two advective components respectively in the x-z and y-z planes. The solid and dashed lines respectively present the over-coupling and under-coupling channels between neighboring sites. c–e plot of the real spectra of the dispersion induced by Hermitian advection respectively at the in-gap corner, gapped edge, and trivial bulk states. The horizontal and vertical axes denote the effective Bloch wave numbers and real value of the eigenvalue. The red and blue dots in (c and d) respectively indicate the corner and edge states.
