Controlling the thermoelectric effect by mechanical manipulation of the electron’s quantum phase in atomic junctions

Abstract

The thermoelectric voltage developed across an atomic metal junction (i.e., a nanostructure in which one or a few atoms connect two metal electrodes) in response to a temperature difference between the electrodes, results from the quantum interference of electrons that pass through the junction multiple times after being scattered by the surrounding defects. Here we report successfully tuning this quantum interference and thus controlling the magnitude and sign of the thermoelectric voltage by applying a mechanical force that deforms the junction. The observed switching of the thermoelectric voltage is reversible and can be cycled many times. Our ab initio and semi-empirical calculations elucidate the detailed mechanism by which the quantum interference is tuned. We show that the applied strain alters the quantum phases of electrons passing through the narrowest part of the junction and hence modifies the electronic quantum interference in the device. Tuning the quantum interference causes the energies of electronic transport resonances to shift, which affects the thermoelectric voltage. These experimental and theoretical studies reveal that Au atomic junctions can be made to exhibit both positive and negative thermoelectric voltages on demand, and demonstrate the importance and tunability of the quantum interference effect in the atomic-scale metal nanostructures.

Remote heat dissipation in atom-sized contacts

“…The asymmetric feature in the thermocouple temperature can be explained by Landauer theory, which predicts a difference in the heat dissipation Δ Q at current upstream ( Q up ) and downstream ( Q down ) of a ballistic system as Δ Q = ( Q up − Q down ) ~ 2 GTSV b , where T and S are the temperature and the Seebeck coefficient, respectively 15 , 22 . On the other hand, while Au nanocontacts are reported to possess structure-dependent bi-thermoelectric properties 23 – 25 , previous studies reported negative thermopower of S Au = −4 μV/K as an average over many configurations measured 24 . Accordingly, Δ Q < 0 from the sign of S Au , and hence Q down > Q up , that explains the higher Δ T t observed under positive V b .…”

Photochemical Reaction Using Aminobenzenethiol Single Molecular Junction

“…Figure 3 shows the conductance change upon rupture of the junction. The conductance trace shows a step at 1 G 0 (2e 2 /h), corresponding to the Au atomic junction [24][25][26]. In the case of the Au atomic junction, a single channel of Au 6s contributes to electron transport, and the transmission of the channel is 100%.…”

Studies on single-molecule bridging metal electrodes: development of new characterization technique and functionalities

“… 27 ) The sign of the thermopower of a material depends on the type of carrier (hole or electron). 28 ) If the carriers are holes, the HOMO stays close to the Fermi level of the single molecular junction. Meanwhile, the I - V curve measurement fixes the energy difference between the Fermi level and the conduction orbital, although it does not indicate whether the conduction orbital is below or above the Fermi level.…”

“…Similar mechanical switches have been reported using bipyridine, BDT, C 60 , Sc 3 N@C 80 , oligothiophene and Au atomic junctions. 28 , 30 , 40 )…”