  Recent studies have shown that there are two types of topological quadrupolar
semimetals. One is the quadrupolar bulk semimetal, which is a conventional
semimetal with gapless nodes in the bulk spectrum. The other type is named the
quadrupolar surface semimetal, possessing a gapped bulk but gapless nodes on
the surface spectrum. There have been many experiments on the implementation of
quadrupolar bulk semimetals. However, the quadrupolar surface semimetal has
never been realized. Here we report on the experimental realization of the
quadrupolar surface semimetal in the circuit system. To highlight the
properties of the quadrupolar surface semimetal, we also prepare a quadrupolar
bulk semimetal in the circuit as a contrast. It has been demonstrated that the
quadrupolar surface semimetal has a bulk band gap, but two gapless nodes appear
on the surfaces. Also, the electrons not only concentrate on the hinges but
also on the corresponding surfaces. Our studies provide novel ways to control
electrical signals and may have potential applications in the field of
intergraded circuit design.
