Early Stage Researcher 9, LEEDS, UNITED KINGDOM


Project title and work package:

Spin-polarised transport in InAs/GaSb coupled quantum well topological edge states, work package Spintronics controlled by spin-orbit interaction.



The main objective of your 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), a low dimensional analogue (providing a link with the work package Electron transport in reduced dimensionality) of the 3D systems that will be studied by Early Stage Researcher 12 (CIC nanoGUNE, Spain), with whom measurement techniques for spin-momentum-locked systems will be jointly developed. You will fabricate QSHE devices from InAs/GaSb coupled well structures in LEEDS and measure them in the quantum spin Hall state. Material growth, device fabrication and gating protocols will be developed in strong collaboration with ETH (Switzerland), where such expertise already exists. Using non-magnetic contacts with a large spin Hall angle (e.g. Pt) grown in LEEDS, you  will be able to detect the spin polarisation of the edge state current through the inverse SHE effect, since it interconverts between spin and charge currents. Through attaching contacts with different spacings, you 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.


Expected Results:

- Coherence length of QSHE helical edge states measured.

- Interaction of spin-polarised injector and spin-momentum locked edges states demonstrated.

- Diode-like response with ferromagnetic contacts measured.


Planned secondments:

at ETH, Switzerland (1 month, Year 1) for training in fabrication and contacting of devices from InAs/GaSb wafer, at RAITH, Germany (2 months, Year 2) for training in nanofabrication & experience of the private sector, at CNRS, France (1 month, Year 3) for training in ultralow temperature techniques and low noise measurements.




Link to apply : https://jobs.leeds.ac.uk/VM/Applications.aspx?jobId=10103