Conduction channels of one-atom zinc contacts

Abstract

We have determined the transmission coefficients of atomic-sized Zn contacts using a new type of breakjunction which contains a whisker as a central bridge. We find that in the last conductance plateau the transport is unexpectedly dominated by a well-transmitting single conduction channel. We explain the experimental findings with the help of a tight-binding model which shows that in an one-atom Zn contact the current proceeds through the 4s and 4p orbitals of the central atom. PACS numbers: 73.40.Jn, 73.63.Rt, 74.50.+r The appearance of experimental techniques such as the scanning tunneling microscope and breakjunctions has allowed to explore the electronic transport at the atomic scale 1 . With these techniques it is possible to gently break a metallic contact and thus form conducting nanowires. During the last stages of the pulling a neckshaped wire connects the two electrodes, the diameter of which is reduced to a single atom upon further stretching. The conductance of these contacts can be described by the Landauer formula: G = G 0 i τ i , where the sum runs over all the available conduction channels, τ i is the transmission for the i th channel and G 0 = 2e 2 /h is the quantum of conductance. As it was shown in Ref.[2], the set of transmission coefficients is amenable to measurement in the case of superconducting materials. Using this possibility it has been established that the number of channels in an one-atom contact is determined by the valence of the metal, and the transmission of each channel is fixed by the local atomic environment 3,4,5 . Thus for instance, an one-contact of a monovalent metal such as Au sustains a single channel, while for sp-like metals such as Al or Pb one finds three channels due to the contribution of the p orbitals, and in a transition metal such as Nb the contribution of the d orbitals leads to five channels. Up to now, these attractive ideas have only been tested in four materials (Au, Al, Pb, and Nb) due to the need of superconductivity for the channel analysis. In this sense, it would be highly desirable to investigate other groups of metals. An interesting possibility is the analysis of the divalent metals of the IIB group of the periodic table such as Zn. The electronic structure of a Zn atom is [Ar]3d 10 4s 2 , i.e. the outermost s orbital is full with two electrons. As a solid, Zn is a conductor due to the overlap between the 4s and the 4p bands. Therefore, for one-atom contacts one expects Zn to be an intermediate case between the noble metals and Al. The goal of this work is to elucidate what determines the conduction channels of one-atom Zn contacts.Traditionally, oxidation problems and the gap anisotropy 6 have prevented the formation of reproducible superconducting contacts with Zn. In order to circumvent these problems we have developed a variation of the mechanically controllable breakjunction (MCB) technique which comprises a Zn whisker as central part. This new technique allows us to fabricate reproducibly oneatom Zn contacts with well-characterized lattic...

Correlation between transport properties and atomic configuration of atomic contacts of zinc by low-temperature measurements

“…20 The sample preparation of the whisker MCBs and the results of these investigations together with a detailed theoretical analysis have been reported before. 14,20 However, the limited lifetime of those contacts hindered the recording of a histogram.…”

Electronic transport in gadolinium atomic-size contacts

“…The groups that are relatively well understood include noble metals, such as Au [5] and Pt [6], sp metals, such as Al [7,8] and Zn [9], ferromagnetic 3d transition metals, such as Fe, Co, and Ni [10], superconductors, such as Pb [1,11,12], and even semimetals such as Bi [13,14]. Besides, some metals like Ir [6], Pt [6], and Au [15,16] form single-stranded chains of atoms.…”

On the Single-Atom Conductance of Ti

“…As seen in the plot, small displacements of electrode atoms significantly change the transmission value from 1.1 to 2.5. Similar calculations made on sp-metals such as Mg [8] and Zn [16] SACs find no such sensitivity of the transmission to structural perturbations. We therefore consider that the observed variation of τ should be a characteristic of d -band SACs.…”

“…The electron energy is measured from the Fermi level and the line at E = 0 in the plot indicates the position of the Fermi level. Previous calculations on some HCP SACs such as those of Mg [8] and Zn [16] yield relatively flat transmission spectra near the Fermi level, and the result is considered due to the sp-character of the valence electrons of these metals. On the other hand, the spectrum depicted in Fig.…”