Shunda Yin

Abstract Non-Hermitian physics — characterized by complex band spectra — established a new paradigm in condensed matter systems and metamaterials. Combined to nonreciprocity, non-Hermitian gain can be arbitrarily injected in a system to manipulate its valley dynamics, leading to phenomena such as the amplified topological whispering gallery modes for acoustic lasing. Here, we reveal that the coupling loss can also be used to manipulate valley degrees of freedom in a phononic metamaterial.

Abstract Quadrupolar topological semimetals with a bulk quadrupole moment have been intensively investigated recently. Of special interest is the quadrupolar surface topological semimetal, which has gapped bulk but surface Dirac nodes attached to each other by hinge states. However, this novel state remains to be observed in condensed matter. Here, we implement the quadrupolar surface topological semimetal in acoustic crystals.