Signatures of Topological Surface State and Unconventional Magnetotransport Properties in Elemental Ruthenium

In recent years, the pursuit of new topological materials has created a vast and ever growing catalogue of compounds. However, the example of elemental topological metals is still rather limited. So far, the non‐trivial topological states have been probed in only a handful of elements and that too rarely in a transition metal. By combining the angle‐resolved photoemission spectroscopy (ARPES) and magnetotransport measurements, here, ruthenium (Ru) is experimentally confirmed to be a topological metal, validating a recent theoretical prediction. The ARPES data for Ru(0001) provide evidence of the topological surface state related to the bulk Dirac node. Ru also exhibits a prominent planar Hall effect, thus further indicating its Dirac semimetallic nature. Large electron and hole mobilities are estimated, which are comparable to several topological semimetals. The non‐trivial nature of electronic band of Ru is also supported by the large non‐saturating transverse magnetoresistance.

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