Student projects

BSc. projects:

Currently there are no projects available.

MSc. projects:

Photocurrents with a twist.

Map of photocurrent measured on a topological insulator surface. Red means positive, blue negative. The sample with gold contact pads on the sides is shown in the background.

Map of photocurrent measured on a topological insulator surface. Red means positive, blue negative. The sample with gold contact pads on the sides is shown in the background.

The optical spectroscopy lab is looking for enthusiastic students for a MSc. thesis project with the ambitious goal to create, investigate and manipulate spin-polarized photocurrents in homemade topological insulator devices.

Topological insulators are a novel class of materials with very special properties. Due to a topological twist in their electronic structure, electrons at the surfaces of these bulk insulators behave as massless Dirac fermions rendering the surfaces metallic. This extraordinary feat is realized due to a dominant role being played by the spin-orbit interaction in these materials. At the same time this also results in a second peculiar behavior: only electrons with a specific spin orientation can flow through these metallic surfaces in a given direction. This implies that if currents are forced to flow through these surfaces, they are necessarily spin-polarized. All these properties together make these materials the ideal playground for applications in spintronics: a new form of technology in which the spin of electrons is used to transmit information rather then by its charge. In the optical spectroscopy lab we have recently build a new setup that uses polarized laser light to force a pico-ampere current flow in a material (only 10^6 electrons/second!). By changing the polarization state of the incoming light, it is possible to observe changes in the photocurrent and differentiate between several origins of the induced photocurrent.

photocurrent

Polarization dependence of the photocurrent at a fixed position. The horizontal axis gives the angle of a quarter wave plate that is used to change the polarization state of the incoming light. 0 degrees corresponds to linear, 45 degrees to circular and 90 degrees to linear again.

The aim of this project is to detect the presence of spin-polarized surface photocurrents in homemade topological insulator devices. To do so you will have to make improvements to the existing photocurrent setup and fabricate your own devices. Most importantly you will have to come up with a clever measurement scheme to exclude other effects, such as thermoelectric currents arising from laser induced heating. The big challenge will be to prove or disprove recent theoretical proposals for the magnitude and polarization dependence of the photocurrents.

The theory heavy nature of this project combined with a challenging experimental task requires background knowledge of condensed matter physics (e.g. GM1 and/or GM2. Photovoltaics is a good alternative.).

For more information please contact Erik van Heumen.