Pt is known to show spontaneous formation of monatomic chains upon breaking a metallic contact. From model calculations, these chains are expected to be spin polarized. However, direct experimental evidence for or against magnetism is lacking. Here, we investigate shot noise as a potential source of information on the magnetic state of Pt atomic chains. We observe a remarkable structure in the distribution of measured shot-noise levels, where the data appear to be confined to the region of nonmagnetic states. While this suggests a nonmagnetic ground state for the Pt atomic chains, from calculations we find that the magnetism in Pt chains is due to actor electron channels, which contribute very little to ballistic conductance and noise. On the other hand, there are weakly polarized spectator channels, which carry most of the current and are only slightly modified by the magnetic state.
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