Effects of spin on transport in single molecule junctions

Spin-based electronics has a large impact on daily life being the back-bone of modern datastorage technology. Exploiting the spin degree of freedom has the potential advantages of non-volatility and decreased electric power consumption as compared to conventional semiconductor electronic devices. Currently the main efforts in the field are directed toward miniaturization of spintronic devices while increasing the spin injection in such devices to maintain a significant response to magnetic field. However, further progress in the field requires a comprehensive understanding of spin transport at the atomic scale. Molecular junctions, composed of a single molecule suspended in between two metallic electrodes, are natural candidates for this task. 

In this talk, I will describe recent experiments conducted on molecular junctions consisting of a benzene molecule bridging two ferromagnetic electrodes in a mechanically controllable break junction device. Using conventional transport measurements, we show that the presence of a molecule in our devices can result in an enhanced response to magnetic field. The magneto-resistive response is found to be tunable by changing the inter-electrode distance. Our findings will be explained in the context of selective orbital hybridization. 

As a complementary perspective, I will describe transport measurements on molecular junctions composed of a paramagnetic molecule, suspended between two non-magnetic silver electrodes. Differential conductance spectroscopy measurements on such molecular junctions reveal both zero-bias and finite-bias conductance peaks. Both peaks are shown to result from Kondo resonances. Moreover, we provide the first unambiguous demonstration of the vibration-mediated Kondo effect. Our experimental results shed light on the nature of electron-vibration interaction in the presence of many-body electron correlation such as a Kondo state.