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.
We present an experimental and theoretical study of the conductance and stability of Mg atomic-sized contacts. Using Mechanically Controllable Break Junctions (MCBJ), we have observed that the room temperature conductance histograms exhibit a series
of peaks, which suggests the existence of a shell effect. Its periodicity, however, cannot be simply explained in terms of either an atomic or electronic shell effect. We have also found that at room temperature, contacts of the diameter of a single atom are absent. A possible interpretation could be the occurrence of a metal-to-insulator transition as the contact radius is reduced, in analogy with what it is known in the context of Mg clusters. However, our first principle calculations show that while an infinite linear chain can be insulating, Mg wires with larger atomic coordinations, as in realistic atomic contacts, are alwaysmetallic. Finally, at liquid helium temperature our measurements show that the conductance histogram is dominated by a pronounced peak at the quantum of conductance. This is in good agreement with our calculations based on a tight-binding model that indicate that the conductance of a Mg one-atom contact is dominated by a single fully open conduction channel.
Suspended chains consisting of single noble metal and oxygen atoms have been formed. We provide evidence that oxygen can react with and be incorporated into metallic one-dimensional atomic chains. Oxygen incorporation reinforces the linear bonds in t
he chain, which facilitates the creation of longer atomic chains. The mechanical and electrical properties of these diatomic chains have been investigated by determining local vibration modes of the chain and by measuring the dependence of the average chain-conductance on the length of the chain. Additionally, we have performed calculations that give insight in the physical mechanism of the oxygen-induced strengthening of the linear bonds and the conductance of the metal-oxygen chains.
Conductance histograms of work-hardened Al show a series up to 11 equidistant peaks with a period of 1.15 +/- 0.02 of the quantum conductance unit G_0 = 2e^2/h. Assuming the peaks originate from atomic discreteness, this agrees with the value of 1.16
G_0 per atom obtained in numerical calculations by Hasmy et al.
