Conduction channels of one-atom zinc contacts

We have determined the transmission coefficients of atomic-sized Zn contacts using a different 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 that shows that in a one-atom Zn contact the current proceeds through the $4s$ and $4p$ orbitals of the central atom.

Figure 1

(Color online) Three-point bending mechanism. The pushing rod bends the bronze substrate. The optical micrograph shows a whisker MCB after measurement. Right inset: an enlargement of a typical Zn whisker with a diameter of $1.7\mu \mathrm{m}$.

Figure 2

Current-voltage characteristics of several one-atom contacts of Zn arranged with a whisker MCB at $T=0.27\mathrm{K}$ (symbols) and best fits to MAR theory (Refs. 14, 15). The value of $\mathrm{\Delta }=160\mu \mathrm{eV}$ was used to fit all the curves. The transmission coefficients obtained from the fit are indicated in the figure. Inset: a typical opening curve recorded at $T=1.5\mathrm{K}$.

Figure 3

Experimental histogram of the channel transmissions ${\tau }_i$ obtained in the last conductance plateau of a Zn-whisker MCB. We count all those contacts as belonging to the last plateau that were recorded when the conductance once dropped to or below $G_0$. The channels are labeled as 1st, 2nd, … according to their ${\tau }_i$’s.

Figure 4

(Color online) (a) Bulk density of states of Zn hcp projected onto the $s$, $p$, and $d$ orbitals as a function of energy. The labels indicate the value of the on-site energies. Inset of panel (b): contact along the [001] direction, with a single central atom and containing 45 atoms. The distance between the different atoms is the bulk distance. (b) and (c) Local DOS at the central atom projected onto the $s$ and $p$ orbitals and channel transmissions as a function of energy for the contact of the inset of panel (b). Notice that the channel $p_x\text{−}{p}_y$ is twofold degenerate. Inset of panel (d): the same contact as in panel (b), but with a dimer in the narrowest part. The distance between the central atoms is the bulk nearest-neighbor distance. (d) and (e) The same as in panels (b) and (c) for the dimer geometry. The Fermi energy is set to zero and is indicated with vertical lines.

Figure 5

(Color online) (a) Channel transmissions as a function of energy for the contact of the inset, which is grown along the [110] direction, has a dimer in the middle, and contains 60 atoms. The Fermi energy is set to zero. (b) Histograms of the transmission coefficients for 3000 disorder realizations (see text) of the one-atom contact of the inset of Fig. 4b.