title: Large Magnetoresistance in Single-Radical Molecular Junctions.
abstract: Organic radicals are promising building blocks for molecular spintronics. Little is known about the role of unpaired electrons for electron transport at the single-molecule level. Here, we examine the impact of magnetic fields on electron transport in single oligo(p-phenyleneethynylene) (OPE)-based radical molecular junctions, which are formed with a mechanically controllable break-junction technique at a low temperature of 4.2 K. Surprisingly huge positive magnetoresistances (MRs) of 16 to 287% are visible for a magnetic field of 4 T, and the values are at least 1 order of magnitude larger than those of the analogous pristine OPE (2-4%). Rigorous analysis of the MR and of current-voltage and inelastic electron-tunneling spectroscopy measurements reveal an effective reduction of the electronic coupling between the current-carrying molecular orbital and the electrodes with increasing magnetic field. We suggest that the large MR for the single-radical molecular junctions might be ascribed to a loss of phase coherence of the charge carriers induced by the magnetic field. Although further investigations are required to reveal the mechanism underlying the strong MR, our findings provide a potential approach for tuning charge transport in metal-molecule junctions with organic radicals.
authors.affiliation: International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science , 1-1 Namiki, Tsukuba 305-0044, Japan.
authors.forename: Ryoma
authors.initials: R
authors.lastname: Hayakawa
authors.forename: Mohammad Amin
authors.initials: MA
authors.lastname: Karimi
authors.forename: Jannic
authors.initials: J
authors.lastname: Wolf
authors.forename: Thomas
authors.initials: T
authors.lastname: Huhn
authors.affiliation: Institute for Inorganic and Applied Chemistry, University of Hamburg , Martin-Luther-King-Platz 6, 20146 Hamburg, Germany.
authors.forename: Martin Sebastian
authors.initials: MS
authors.lastname: Zöllner
authors.affiliation: Institute for Inorganic and Applied Chemistry, University of Hamburg , Martin-Luther-King-Platz 6, 20146 Hamburg, Germany.
authors.forename: Carmen
authors.initials: C
authors.lastname: Herrmann
authors.forename: Elke
authors.initials: E
authors.lastname: Scheer
keywords: Single organic radicals; charge transport; large magnetoresistance; mechanically controllable break junction