title: Quantum thermopower of metallic atomic-size contacts at room temperature.
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.
authors.affiliation: Departamento de Física de la Materia Condensada and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid , E-28049 Madrid, Spain.
authors.forename: Charalambos
authors.initials: C
authors.lastname: Evangeli
authors.forename: Manuel
authors.initials: M
authors.lastname: Matt
authors.forename: Laura
authors.initials: L
authors.lastname: Rincón-García
authors.forename: Fabian
authors.initials: F
authors.lastname: Pauly
authors.forename: Peter
authors.initials: P
authors.lastname: Nielaba
authors.forename: Gabino
authors.initials: G
authors.lastname: Rubio-Bollinger
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Cuevas
authors.forename: Nicolás
authors.initials: N
authors.lastname: Agraït
mesh_terms: D006046:Gold / Q000737:chemistry*; D016252:Microscopy, Scanning Tunneling; D056004:Molecular Dynamics Simulation; D010984:Platinum / Q000737:chemistry*; D011789:Quantum Theory; D013696:Temperature
chemical_list: D010984:Platinum; D006046:Gold
keywords: Landauer approach; Quantum thermopower; atomic-size metallic contacts; molecular dynamics simulations; quantum conductance