Single-molecule photo-spintronics

Spintronics is like electronics except that it uses the spin of the electron (a quantum mechanical property that behaves like angular momentum and is closely linked to magnetism) as well as the electron's electric charge. Using spin and charge together could lead to computers that use much less energy, for example. Photo-spintronics adds light to the mix. This is very useful because light can easily carry information over long distances (think of optic fibres). Light and spin are also key to future quantum technologies such as quantum computing and quantum information.

Our research is to find ways of using organic molecules, based on chains and rings of carbon atoms, in photo-spintronics. This is an exciting prospect because carbon has a low atomic number which reduces the chances of losing spin information, and because there are so many different organic molecules and ways of linking them that the opportunities to find new and useful phenomena are practically endless. Our plan is to study single molecules linking a semiconductor and a magnetic metal. Single molecule experiments are difficult but not impossible, and we have made them successfully in the past using a modified scanning tunnelling microscope. Single molecule studies have helped greatly in understanding molecular electronics because studying molecules individually reveals information that is lost when they are measured in a large group.

Ours will be the first single molecule studies in photo-spintronics. We will create a population of excited electrons in the semiconductor by illuminating it and use the polarization of the light to control the spin of the electrons. We will then measure the current between the semiconductor and the ferromagnetic metal. If the current depends on the polarization of the light and the direction in which the metal is magnetized, that will be evidence that spin is being transported through the molecules. Once we show that we can make photo-spintronic measurements through a single molecule, we will investigate how the spin transport depends on the type of semiconductor, the metal, the voltage between the two (known as the bias), and the types of chemical bond between the molecule and the semiconductor and metal. This will show us how best to use organic molecules in future spintronic and photo-spintronic devices.