We have studied electron transport through Ni/1,4-benzenedithiol (BDT)/Ni single molecule junctions at cryogenic temperatures under magnetic field up to 250 mT. Instead of examining magnetoresistance (MR) of individual junctions, we measured the conductance of many junctions under a constant magnetic field and investigated how a single-molecule peak in a conductance histogram shifts with the field strength. We found that the single-molecule resistance at 77 K, deduced from the conductance peak position, shows a hysteresis against the field strength and takes a maximum around 50 mT when the magnetic field increases from 0 T to 150 mT. The observed resistance change yields a MR of $ð80À90Þ% for Ni/BDT/Ni single molecule junctions. This MR is higher than experimental MR reported for non-conjugating molecules but consistent with high theoretical MR predicted for p-conjugated molecules such as BDT. We have also investigated the nonlinearity of the current-voltage (IÀV) characteristics of Ni/BDT/Ni junctions under 0 T and 150 mT and found that the nonlinearity changes its sign from negative at 0 T to positive at 150 mT. This result suggests that the junction transmission spectrum at 0 T should have a low-lying peak within 60:1 eV from the Fermi level, but the peak moves out of the bias window when the magnetic field increases to 150 mT. The observed field-induced change in the IÀV nonlinearity is qualitatively consistent with theoretical IÀV curves of Ni/BDT/Ni calculated for magnetized and non-magnetized Ni electrodes. V

We studied the conductance of Au/1,4-benzenedicarbothioamide (BDTA)/Au junctions at room temperature and measured a single-molecule conductance of BDTA. A carbothioamide (thioamide, −CSNH 2) group of this molecule consists of two potential linkers, thioketone and amine groups, and would thus be expected to show high conductance. The experimental single-molecule conductance of BDTA is (0.8 − 1.0) × 10 −3 G 0 which roughly compares with that of π-conjugated molecules. We consider that this relatively high conductance of Au/BDTA/Au is due to the homoconjugation of π-orbitals of benzene and sulfur while the amine group is likely to remain as a side group. We also observed that Au/BDTA/Au junctions can exist in multiple configurations of different conductances.