Spin-polarised transport in InAs/GaSb coupled quantum well topological edge states (Prof. Christopher Marrows)

The main objective of this project is to measure directly and exploit the perfect spin-polarisation of currents carried by the edge states in InAs/GaSb quantum spin Hall systems, which arises through spin-momentum locking. This system is a two-dimensional topological insulator (TI), capable of being grown by molecular beam epitaxy in Leeds.

The successful candidate will fabricate QSHE devices from InAs/GaSb coupled well structures and measure them in the quantum spin Hall state. Using non-magnetic contacts with a large spin Hall angle (e.g. Pt), he/she will be able to detect the spin polarisation of the edge state current through the inverse SHE effect, since the iSHE interconverts between spin and charge currents. Through attaching contacts with different spacings, he/she will measure the length over which the edge state current is coherent. This will set the scale at which a system of devices that exploit this effect must be manufactured.

Meanwhile, if current is driven between two ferromagnetic contacts (e.g. NiFe) that are separated by less than this length, a diode-like response should be found where different conductances are measured in different directions, since the spin-polarisation of the contacts defines a unique direction of current flow in the QSHE system. The ratio of conductances in the forward and reverse bias directions will provide a measure of the spin-polarisation of the carriers.