Oscillatory thermopower of carbon chains: First-principles calculations

We investigate the thermoelectric transport through carbon chains connected by two Al leads. Using a Landauer-Buttiker-like formula, we calculate the thermopower and thermoconductance of $\mathrm{Al}\text{‐}{\mathrm{C}}_n\text{‐}\mathrm{Al}$ from first principles. We find that the charge transfer plays an important role in the thermoelectric transport. Because of the charge transfer, the thermopower changes sign for even-odd number of carbon atoms. The thermopower and electric conductance as a function of the gate voltage also exhibit oscillatory behaviors with a phase difference of $\pi ∕2$.

Figure 1

(Color online) The thermopower vs temperatures for $\mathrm{Al}\text{‐}{\mathrm{C}}_n\text{‐}\mathrm{Al}$ junction with $n=5$ (solid line), $n=6$ (dotted line), $n=7$ (dot-dashed line), $n=8$ (short dashed line), and $n=9$ (long dashed line). The unit of the thermopower is $\mu \mathrm{V}∕\mathrm{K}$ and the temperature is measured in K. Right inset: schematic plot of the $\mathrm{Al}\text{‐}{\mathrm{C}}_5\text{‐}\mathrm{Al}$ device.

Figure 2

The charge transfer vs gate voltage (in a.u.) for different carbon chains with $n=5$ (solid circle), $n=6$ (open circle), $n=7$ (solid square), $n=8$ (open square), and $n=9$ (triangle).

Figure 3

The electric conductance vs gate voltage for different carbon chains. Here the symbols are the same as in Fig. 2.

Figure 4

The thermopower at 5 K vs gate voltage for different carbon chains. Here the symbols are the same as in Fig. 2.

Figure 5

The charge transfer (solid square), the electric conductance (solid circle), and the thermopower at 5 K (open circle) vs the gate voltage.