Physics of “spintronic” materials

Supervisor: Dr Ben Murdin

Major Aims:
To investigate the physics of “spintronic” materials, using ultra-fast lasers, very high magnetic fields, and very high pressures as diagnostic techniques.

Techniques used and source of expertise:
Infrared spectroscopy of novel low-dimensional semiconductor structures, measurement of excited state lifetimes using a picosecond laser at FELIX in the Netherlands, and non-linear absorption techniques. High pressure and high magnetic field spectroscopy of such materials.

Very recently a new concept for semiconductor memory has been developed based on electron spin. In special materials the energy states of electrons with different spin are non-degenerate (i.e. they are at different energy) even without a magnetic field. This opens up the possibility to design circuits in which electrons remember their spin even as they flow through the circuit. However, relatively little is understood about the magnitude of this effect, and how to improve the length of time before the memory is lost (the spin-flip time).

There will be two aspects to this project. One will involve measurement of the spin-flip lifetimes in various quantum confined semiconductor spintronic materials with a direct time-resolved technique, using a picosecond pulsed laser in the Netherlands. The other will be to measure the electron spin transport of the materials while under extreme high pressures and/or magnetic fields. The effect of magnetic fields on spin states is given, broadly speaking, by the well-known Zeeman effect. It would be interesting to know how much the spin-flip times can be improved by such fields, and this will also help the design of better zero-field memory. High pressure is another useful diagnostic tool since it changes the electronic states of the semiconductor in a way very similar to changing alloy compositions. It allows testing of ideas about how properties such as the spin-flip time should depend on the alloy composition and configuration of electronic states. This information can be used to improve the design of the quantum confinement etc.

Depending on the time-scale we may be able to take advantage of the new ultra-fast laser and high pressure facilities of the new Advanced Technology Institute.