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Anomalous Transport and Possible Phase Transition in Palladium Nanojunctions

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Gavin D. Scott†*, Juan J. Palacios‡ and Douglas Natelson†§

^† Department of Physics and Astronomy, Rice University, 6100 Main Street, Houston, Texas 77005

^‡ Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, Madrid 28049, Spain

^§ Department of Computer and Electrical Engineering, Rice University, 6100 Main Street, Houston, Texas 77005

ACS Nano, 2010, 4 (5), pp 2831–2837

DOI: 10.1021/nn1000172

Publication Date (Web): April 20, 2010

* Address correspondence to gavin.scott@rice.edu.

Section:

Electric Phenomena

Abstract

Many phenomena in condensed matter are thought to result from competition between different ordered phases. Palladium is a paramagnetic metal close to both ferromagnetism and superconductivity and is, therefore, a potentially interesting material to consider. Nanoscale structuring of matter can modify relevant physical energy scales, leading to effects such as locally modified magnetic interactions. We present transport measurements in electromigrated palladium break junction devices showing the emergence at low temperatures of anomalous sharp features in the differential conductance. These features appear symmetrically in applied bias and exhibit a temperature dependence of their characteristic voltages reminiscent of a mean-field phase transition. The systematic variation of these voltages with zero bias conductance, together with density functional theory calculations illustrating the relationship between the magnetization of Pd and atomic coordination, suggests that the features may result from the onset of spontaneous magnetization in the nanojunction electrodes. We propose that the characteristic conductance features are related to inelastic tunneling involving magnetic excitations.