Putting spin into carbon nanoelectronics

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Single walled carbon nanotubes are proving themselves to be remarkable candidates for disruptive nanoelectronic devices. Electrons can flow through them ballistically, which means that they travel without being scattered by features in the material of the nanotube. It is possible to make transistors with single walled nanotubes with both electron and hole conductors, thus providing components for complete logic circuits. It is even possible to make transistors which work with a change of only a single electron in the active region. All of this could be very significant for future electronics applications, but that would be only the beginning, because these devices use only the charge on the electron. There is another secret weapon which can be used, in the form of the electron spin.The electron spin can be thought of as a tiny magnet, which can point in one of two directions (often referred to as up and down). The new field of electronics which this opens up already has a name, spintronics, and its own Nobel Prize Winners. The biggest current application of spintronics is in the heads for reading data on hard discs in computers, revolutionizing this multibillion dollar industry. Magnetic random access memory is now being made and sold, with the promise of ever higher access speeds. The search is on for new materials systems which can be used for spintronic devices, which may in turn be exploited in new applications. New effects are being discovered all the time. For example, if you apply different temperatures to the two ends of a metallic magnet, a current of electron spins can flow.Our vision is to put spin into carbon nanoelectronics. If we can do this, we may be able to add a whole new capability to what is already possible with nanotube transistors. For this purpose we shall use other carbon materials, even smaller than nanotubes, in the form of cages called fullerene molecules (also known as Bucky balls). These molecules can each contain one or more atoms which carry a resulting electron spin. They can be inserted into single walled nanotubes, and the resulting structures are sometimes called peapods, because that is what they look like in an electron microscope. Peapods provide an ideal way to put spin into nanotubes.In our research programme, we shall fabricate peapod transistors, and look at them by high resolution transmission electron microscopy under conditions which minimise the damage to the samples. In this way we shall be able to see with atomic resolution the very piece of material which is active in the device. We shall measure the current through the transistor while we vary the magnetic field and the temperature, and look for effects which may be very sensitive to one or other of these. We shall apply microwave radiation, and detect the effect on electrical conductance as we sweep the magnetic field through the spin resonance. Finally we shall perform controlled experiments to measure electrically the direction of the spin.Although these are fundamental experiments, our hope is that they will lead to practical applications. These may be through the effects of collective excitations, for applications such as nanoelectronic circuits and sensors, or they may be through direct control of the spin states, for more revolutionary devices such as quantum logic devices, quantum memories and perhaps even eventually quantum computing.