Observation of bulk quadrupole in topological heat transport

This paper reports the generation of quantized bulk quadrupole moments in fluid heat transport and the observation of quadrupole topological phases in non-Hermitian thermal systems. Experiments demonstrate hierarchical features of bulk, gapped edge, and in-gap corner states in both real- and imaginary-valued bands, unlike previous observations in classical wave fields. This work opens possibilities for diffusive metamaterial engineering and multipolar topological physics.

Guoqiang Xu, Xue Zhou, Shuihua Yang, Jing Wu, Cheng-Wei Qiu