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Quantum thermopower of metallic atomic-size contacts at room temperature

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Published
  • Charalambos Evangeli
  • Manuel Matt
  • Laura Rincón-García,
  • Fabian Pauly
  • Peter Nielaba
  • Gabino Rubio-Bollinger
  • Juan Carlos Cuevas
  • Nicolas Agrait
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<mark>Journal publication date</mark>11/02/2015
<mark>Journal</mark>Nano Letters
Issue number2
Volume15
Number of pages6
Pages (from-to)1006-1011
Publication StatusPublished
Early online date21/01/15
<mark>Original language</mark>English

Abstract

We report conductance and thermopower measurements of metallic atomic-size contacts, namely gold and platinum, using a scanning tunneling microscope (STM) at room temperature. We find that few-atom gold contacts have an average negative thermopower, whereas platinum contacts present a positive thermopower, showing that for both metals, the sign of the thermopower in the nanoscale differs from that of bulk wires. We also find that the magnitude of the thermopower exhibits minima at the maxima of the conductance histogram in the case of gold nanocontacts while for platinum it presents large fluctuations. Tight-binding calculations and Green’s function techniques, together with molecular dynamics simulations, show that these observations can be understood in the context of the Landauer–Büttiker picture of coherent transport in atomic-scale wires. In particular, we show that the differences in the thermopower between these two metals are due to the fact that the elastic transport is dominated by the 6s orbitals in the case of gold and by the 5d orbitals in the case of platinum.