Tunable magnetoresistance in an asymmetrically coupled single molecule junction

Phenomena that are highly sensitive to magnetic fields can be exploited in sensors and non-volatile memories1. The scaling of such phenomena down to the single-molecule level2,3 may enable novel spintronic devices4. Here, we report magnetoresistance in a single-molecule junction arising from negative differential resistance that shifts in a magnetic field at a rate two orders of magnitude larger than Zeeman shifts. This sensitivity to the magnetic field produces two voltage-tunable forms of magnetoresistance, which can be selected via the applied bias. The negative differential resistance is caused by transient charging5,6,7 of an iron phthalocyanine (FePc) molecule on a single layer of copper nitride (Cu2N) on a Cu(001) surface, and occurs at voltages corresponding to the alignment of sharp resonances in the filled and empty molecular states with the Cu(001) Fermi energy. An asymmetric voltage-divider effect enhances the apparent voltage shift of the negative differential resistance with magnetic field, which inherently is on the scale of the Zeeman energy8. These results illustrate the impact that asymmetric coupling to metallic electrodes can have on transport through molecules, and highlight how this coupling can be used to develop molecular spintronic applications

Electronic and geometric structure of Si(111)-5X2-Au

Si(111)-5x2-Au is investigated in detail using scanning tunneling microscopy and spectroscopy at 78 K. It is shown that topographic features in STM images are strongly dependent on bias voltages, including a new atomic feature, V unit. Detailed investigations of local distributions of electronic states by scanning tunneling microscopy, point spectroscopy, and current imaging tunneling spectroscopy suggest extensive charge transfers between intra- and interlocal unit cells. Comparisons of experimental and theoretical structural models proposed up to date are made and it is found that none of models truly reproduces all the features observed so far. Our findings suggest that further investigation is required.open1131sciescopu