Non-Hermitian Chiral Heat Transport

Exceptional point (EP) has been captivated as a concept of interpreting eigenvalue degeneracy and eigenstate exchange in non-Hermitian physics. The chirality in the vicinity of EP is intrinsically preserved and usually immune to external bias or perturbation, resulting in the robustness of asymmetric backscattering and directional emission in classical wave fields. Despite recent progress in non-Hermitian thermal diffusion, all state-of-the-art approaches fail to exhibit chiral states or directional robustness in heat transport. Here we report the first discovery of chiral heat transport, which is manifested only in the vicinity of EP but suppressed at the EP of a thermal system. The chiral heat transport demonstrates significant robustness against drastically varying advections and thermal perturbations imposed. Our results reveal the chirality in heat transport process and provide a novel strategy for manipulating mass, charge, and diffusive light.

Figure 1

Schematic of non-Hermitian chiral heat transports. (a) A conventional convective heat transport system without constant thermal perturbations. Two wavelike advection are, respectively, imposed to the upper and lower boundaries. The gray wave packets denote the eigenstates of heat transport under different configurations of the upper and lower advections, and the orange one indicates the initial state without advections. The green arrows indicate the corresponding propagation directions, which are determined by the most dominating advection showcasing different directional biases. (b) The chirality in heat transport under constant thermal perturbations and advections. The eigenstates exhibit robust and same directions. (c) and (d) The real and imaginary eigenvalues of the heat transport in regions $A$ and $B$, while the thermal distributions (color map) of the upper and lower subparts solely induced by corresponding advection are presented in the inset of (d).

Figure 2

Chiral heat transport in region $A$. (a) The transformation between the schematic and experimental models via conformal mapping. The corresponding boundaries between the two spaces are marked by red and blue lines. The counteradvection along the parallel direction in the Cartesian coordinate transform to a pair of CW and CCW spinning on the upper and lower fluidic surfaces. The meshes indicate the spatial distributions of the transformation. (b)–(d) The temperature distributions and thermal profiles of three cases in region $A$ on the measured lines (purple dashed lines), respectively, with different advective configurations. The insets present the calculated (left) and experimental (right) thermal distributions. (e) presents the coupled phase transitions of the final state. The green line is theoretically calculated by Considering the additional phase transitions caused by the velocity differences, and the dots refer to those selected cases. The orientations of the coupled phase transitions are robustly towards CW, even though the velocity of CW spinning is smaller.

Figure 3

Nonchiral heat transports in region $B$. (a)–(c) The temperature distributions in region $B$ under varied advective configurations. The upper and lower images are the simulated and experimental temperatures of these cases. Nonchiral heat transports without biased direction are significant. The purple-dashed lines denote the measured lines. Panels (d)–(f), respectively, denote the characteristic temperature distributions of (a)–(c) on the measured lines (purple dashed lines).

Figure 4

Thermal manipulations induced by the chiral and nonchiral heat transports. (a)–(d) The captured temperature profiles of cases 1–3, the black-dashed borders indicate the fluidic area. Among them, (a) and (b) present the profiles of cases 1 and 2 induced by the nonchiral heat transports. (c) and (d) illustrate the unidirectional twist profiles of case 3 induced by the chiral states of area IV.