Abstract
Tensor monopole is a topological singularity in four-dimensional space, associated with tensor gauge field. Unlike odd-dimensional monopoles in the A class, tensor monopoles belong to the AIII class and preserve chiral symmetry. Here, we reveal and observe some unique topological phenomena in acoustic tensor monopole semimetals:
- We explore bulk-boundary correspondence in 4D tensor monopole semimetals. Then, we observe topological boundary states in synthetic acoustic tensor monopole semimetals. Remarkably, we realize surface Dirac cones in these three-band semimetals.
- Tensor monopole acts as a Berry dipole in the sub-3D space, which hosts a dipolar Berry-curvature field. we experimentally demonstrate unconventional oriented Landau levels, wherein by reversing the orientation of the pseudomagnetic field, the system exhibits distinct Landau spectra. Remarkably, we observe a new type of helical zero modes whose existence critically depends on the magnetic field's orientation.
- When breaking down chiral symmetry in tensor monopole systems, we propose a novel topological structure in 4D: Weyl rings, characterized by the first Chern numbers, and Fermi surface boundary states.