Molecular dynamics study of the thermopower of Ag, Au, and Pt nanocontacts

TL;DR

This study uses molecular dynamics simulations to analyze the thermopower behavior of atomic contacts in Ag, Au, and Pt, revealing how atomic structure influences thermopower fluctuations and aligning with experimental observations.

Contribution

It provides the first atomistic explanation for thermopower fluctuations in atomic contacts, highlighting the role of electronic structure and conductance channels.

Findings

Thermopower averages to zero with increasing fluctuations for smaller junctions.

Fluctuations are suppressed in s-valent metals with single transmission channels.

Pt shows larger thermopower fluctuations and no suppression pattern.

Abstract

Using molecular dynamics simulations of many junction stretching processes we analyze the thermopower of silver (Ag), gold (Au), and platinum (Pt) atomic contacts. In all cases we observe that the thermopower vanishes on average within the standard deviation and that its fluctuations increase for decreasing minimum cross-section of the junctions. However, we find a suppression of the fluctuations of the thermopower for the s-valent metals Ag and Au, when the conductance originates from a single, perfectly transmitting channel. Essential features of the experimental results for Au, Ag, and copper (Cu) of Ludoph and van Ruitenbeek [Phys. Rev. B 59, 12290 (1999)], as yet unaddressed by atomistic studies, can hence be explained by considering the atomic and electronic structure at the disordered narrowest constriction of the contacts. For the multivalent metal Pt our calculations predict the fluctuations of the thermopower to be larger by one order of magnitude as compared to Ag and Au, and suppressions of the fluctuations as a function of the conductance are absent.