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Charge Transport in a Zn-Porphyrin single molecule junction

We have investigated charge transport in ZnTPPdT-Pyr molecular junctions using the lithographic MCBJ technique at room temperature and cryogenic temperature (6K). We combined low-bias statistical measurements with spectroscopy of the molecular levels using I(V) characteristics. This combination allows us to characterize the transport in a molecular junction in detail. This complex molecule can form different junction configurations, which is observed in trace histograms and in current-voltage (I(V)) measurements. Both methods show that multiple stable single-molecule junction configurations can be obtained by modulating the inter-electrode distance. In addition we demonstrate that different ZnTPPdT-Pyr junction configurations can lead to completely different spectroscopic features with the same conductance values. We show that statistical low-bias conductance measurements should be interpreted with care, and that the combination with I(V) spectroscopy represents an essential tool for a more detailed characterization of the charge transport in a single molecule.