Interplay between Magnetoresistance and Kondo Resonance in Radical Single-Molecule Junctions

Abstract

We report transport measurements on tunable single-molecule junctions of the organic perchlorotrityl radical molecule, contacted with gold electrodes at low temperature. The current−voltage characteristics of a subset of junctions shows zerobias anomalies due to the Kondo effect and in addition elevated magnetoresistance (MR). Junctions without Kondo resonance reveal a much stronger MR. Furthermore, we show that the amplitude of the MR can be tuned by mechanically stretching the junction. On the basis of these findings, we attribute the high MR to an interference effect involving spin-dependent scattering at the metal−molecule interface and assign the Kondo effect to the unpaired spin located in the center of the molecule in asymmetric junctions.

Controlling Spin Interference in Single Radical Molecules

“…Redox-addressable Verdazyl radicals show bias-dependent rectification and promise a single molecule transistor-like switching even at room temperature . Moreover, Kondo resonance has been observed in polychlorotriphenylmethyl radicals. , …”

“…13 Moreover, Kondo resonance has been observed in polychlorotriphenylmethyl radicals. 1,14 Due to their small size and atomically precise structure, molecules exhibit quantum effects such as quantum interference (QI) even at room temperature. 15−20 This has been demonstrated recently in closed-shell polycyclic aromatic hydrocarbons (PAHs).…”

Magnetoresistance originated from the Au/S interface in Au/1,6-hexanedithiol/Au single-molecule junctions at room temperature

“…The spin scattering model proposed by Mitra et al 13 would not be appropriate because only positive MR is observed for a variety of structures in the study. Our results could be explained by modifying the mechanism related to the formation of S and T transport channels proposed by Xie et al 14 They suggested that an unpaired charge is localized in the aromatic molecule at the S side and the coupling between the localized charge and transported charge produces S and T transport channels.…”

“…The MR of singlemolecule junctions with Au/S bonds has been indicated in some studies. 12,13 Various mechanisms have been proposed as follows.…”

Enhanced Electron Transport in Nonconjugated Radical Oligomers Occurs by Tunneling

“…Radical polymers (i.e., macromolecules where pendant radical species are attached to a nonconjugated backbone) have emerged as new functional materials for applications in electronic devices such as batteries, memristors, and diodes due to their unique redox, optical, and electronic properties. − Organic radical species are open-shell systems with unpaired electrons that have attracted extensive interest in controlling molecular electronics properties such as the Kondo effect and magnetoresistive phenomena. − However, the fundamental charge transport mechanisms of organic radical species are not fully understood. Recent advances in single-molecule characterization have enabled the study of charge transport mechanisms in organic materials at the single-molecule level using experimental techniques such as the mechanically controllable break junction (MCBJ) and the scanning tunneling microscope–break junction (STM-BJ) .…”