 The question really is about the quantum spin-haul effect and then I probably should say a bit more about the spin-haul effect first Which is a an effect that that Semiconductor transport people were after say in the early 2000s an effect you to spin orbit coupling in these materials That could lead to new functionalities for spin-tronic devices Which which will be then switches that that dissipate very small energy So we were working on our Wetzburg material to study this effect when there came a prediction from two colleagues from Philadelphia to theorists that there might also be a Quantized version of the spin-haul effect where actually You would get a quantum Hall effect at zero magnetic field. The question really was How do you do such an experiment? What is the right material to to use it in? The suggestion of Kane and Melle at that time was to use graphene, but then a graphene with an artificially high Spin-obert coupling also of next nearest neighbor type, which was not very physical I knew at that time that that our material not only had a murky tellerite Not only had a strong spin-obert coupling, but it also has a weird inverted band structure and because of this inverted band structure It had a surface state Occuring even when the bulk was insulating metallic surface states I thought this might be something related to this this Kane and Melle proposal and they discussed this band structure with such a Zhang a theorist from Stanford gave him a Teases a PSD taser describing our band structure calculations very soon He came back with a theory which is now known as the BHZ theory Showing that indeed if you make a quantum wall of murky tellerite You can expect to see the quantum spin-haul effect well before this paper was published We were already doing the experiment because we were talking with the guys They're around the same time the BHZ paper was published in our experiments around Christmas We saw quantization of the spin-haul effect quantized at conductance in very small Nanostructures made out of murky tellerite quantum wells The methods that we use in the end is is transport physics. We measure the conductance of Electronic devices this starts with the growth of the material Our materials are pretty special semiconductors We have to grow them layer by layer in something we call a molecular beam epitaxy machine Which is ultra high vacuum technology. So that's very extensive growth technology Then we have to pattern these these samples into very small structures had just like the Transistors in the chips that you use in your cell phone We use very similar structures to do our what we call transport experiments to really see the effects that that we Want to see because they occur at very small distances So we have to make very small devices for that we have a lithography lab in which work and once we have our devices We do these conductance measurements, which we call transport experiments We usually need to do them at very low temperatures. So we use very extensive cryogenic equipment cryostats to perform them the key findings of these first experiments were well Actually pretty prosaic. What we saw is a Quantized conductance of these devices in this so-called quantum spin Hall regime and quantized means quantized in the sense of a quantum Hall effect There is this thing that that physics physicists have discovered Which is the a conductance quantum, which is the square of the electron charge divided by Planck's constant And that conductance actually is what we also observed in our devices later on if you develop topology further in in in other materials We have done things like discovery of the quantum Hall effect in a three-dimensional topological insulator Again, this was possible because of the high crystalline quality of our materials more recently We have been looking at at a topological superconductivity there We have found a a store called for pi dependence of the superconducting proximity effect on the difference between the superconducting electrodes you have in these devices and that's a Pretty sure sign that you have what some people call Majorana modes in your material Which are the modes that give rise to Majorana bound states that zero energy if you can can localize them So there there is sign that indeed you have topological superconductivity going on in this materials and that in principle You could be able to use it for topological quantum computing The main relevance of these findings is is the realization that physicists miss something when they develop band structure theory in the 30s It's it's a rather big big omission. You can really look at Papers from the 30s and you see that people are talking about surface states and are very close to the realization There could be surface states that are Intrinterically linked to the band structure, but they never really made that step these surface states of our material They also were something that the community knew about for something like 20 years Before this connection came with topology and this connection with topology, of course It's a very very strong thing because now you can can use all kinds of topological mathematics on the description of these band structures and You can describe further effects the important discovery really was that band structures can have topological properties and that they lead to Totally new physics in these materials. There are also maybe applications, but that's secondary I guess and the applications could be that these s-channels we saw in the two-dimensional quantum spin-haul effect Could give you a very low power possibilities for Computation, but you have to get the effect of room temperature and that's that's not so easy The other thing is that these myoranum modes I talked about in the topological superconductivity could be used to Try topological quantum computing with some people see as a very promising Road to go for quantum computing, but again, these are things that that still have to be Demonstrated and we have to see how far all this develops Doing the physics of course is very exciting of all these novel aspects So one of the things that we're working on very extensively right now is this topological superconductivity Our group actually is kind of a newbie in this field. We have little Superconducting background. It's close enough to us, of course because we are transport physicists So we developing this in many different directions many different systems One important thing is to take it to two high frequencies where things are a lot more stable for topological superconductivity Another direction that's becoming very important is looking at the rock and wild systems where we can Make topological band structures that mimic the dispersion of elementary particles This allows us to actually go after some effects that particle theorists have predicted for imaginary particles We can actually now create a band structure in our semiconductor devices that mimics the Hamiltonians that these people study And we can try and demonstrate the effects that they have been predicting a final road is that that we work But this is with a different material system, which is a magnetic topological insulator Which shows something called the quantum anomalous Hall effect, which is a single spin version of the quantum spin Hall effect And this shows very good quantum whole quantization at zero magnetic field but at Still at very low temperatures, but this is something that the metrology people are very interested in because developing a Quantum metrology standard that works at zero magnetic fields can have a big Implications for for their labs, so we collaborate for example with BTB Brown swag about this