International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science , 1-1 Namiki, Tsukuba 305-0044, Japan.
Institute for Inorganic and Applied Chemistry, University of Hamburg , Martin-Luther-King-Platz 6, 20146 Hamburg, Germany.
Nano Lett. 2016 Aug 10;16(8):4960-7. doi: 10.1021/acs.nanolett.6b01595. Epub 2016 Aug 1.
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.
有机自由基是分子自旋电子学有前途的构建块。对于单分子水平上未配对电子在电子输运中的作用知之甚少。在这里，我们研究了磁场对低温 4.2 K 下机械可控断键技术形成的单聚对亚苯基乙炔（OPE）基自由基分子结中电子输运的影响。令人惊讶的是，磁场为 4 T 时，可观察到高达 16%至 287%的巨大正磁电阻（MR），其值至少比类似的原始 OPE（2-4%）大一个数量级。对 MR 和电流-电压以及非弹性电子隧道光谱测量的严格分析表明，随着磁场的增加，载流子分子轨道与电极之间的电子耦合有效降低。我们认为，单自由基分子结中较大的磁电阻可能归因于磁场诱导的载流子相位相干的损失。尽管需要进一步的研究来揭示强磁电阻的机制，但我们的发现为使用有机自由基调谐金属-分子结中的电荷输运提供了一种潜在的方法。
