In lesson 9. Sorry, Mark, did I forget about guarding? No, sorry. It's me. I'm very sorry. Yeah. That's me. Yeah. Yeah. Please go on. Yes. So we're going to do is like that where it's gap in the board. By the surface. It's, it's goblet is metallic, is conducting. And it's not just like any trivial conductor like goal is more like graphing. So the linear and the enemy's dispersion when the surface is linear. Where you have, when I'm, when I'm recently here where my pointer is actually these linear dispersion, but only on the surface while the book is got. So that's a, that's how a topological insulator it, so it's, it's a materialize in, I would say this is not a mirror, right? It's not a it's not an insulator. But I would say this is the metal on the surface. There is not any medalist, is a topological surface states and the bulk is completely gap. So they supposedly the bulb is not, is an insulator. So there is no conduction through the bulk, but all the conduction through the surface. So that kind of material, it exists, it has been shown that it exists probably from the early 20 tens. And again, if it's actually, it's very interesting because HE surface of this polygon material to how it can allow, allow electrons to flow. But not any electrons, actual electrons with particular speeds. So as I'm trying to depict here on the, on the, on the right, is you pass scoring one direction. Let's say you bus going from left to right. You can, you are telling the electron which type of a spin new one, because only one speed will propagate if you pass current from left to right, that would be, let's say speeds that are facing. That would be kind of speeds that are facing on to the, to the, to the left side of the crystal. If you pass scoring on the, on the reverse way, the SPI will be facing the other direction, the opposite direction. So you can control the spin direction, the spinless electron by depending on how, how you're flowing current. So that's one of the properties that we call actually lead to political protection. Because that means if there is a defect on the surface, the electrons have no other choice than, than surround the defect and keep going. There is no choice for back scattering because there is only one type of spin that can be in, there can be moving if you're passing querying one direction. So that's all because the public by protection there for this tuple lake and materials are desirable because they can, they can be, they can be good for reducing back scattering. Why do we care about scattering? So by cutting actually is one reason why we have resistance. So resistance, electrical resistance, what it does, it, it actually consumes energy right at the end of the day. It, it, it can convert energy into heat. And then when we won actually very good conductors, we don't want bad conductors because back scattering actually kind of January's by conductors in that sense. So the double Eva protection is something desirable from this top polygon materials. And the other thing that is interesting for materials is like, as I say, the surface, these linear dispersion. So is like electrons on the surface behave like light. They, they are, they don't behave like electrons on. Metals are electrons in semiconductors. They behave like electrons. More, they became more like light with, as you can see here, is a Hamiltonian where he sang HBr, thermal velocity, wave vector times these real spin part. So they are the only depends on the wave vector, not in the wave vector squared. So it's, it's linear. It's again linear in an expression like in graphene, graphene like physics. So that's why these topics are interesting. But so that a lot of research about the political insulators. But now, what, what can we do with this Tupelo good insulator? So one thing that people were thinking, or actually there are several things that people always think. What can we use these two particular insulators for? So one thing is like creating a combining two polygons here for abbreviation is DI with magnetism. So you can create these quantum anomalous oil that has been already up, sir. Quantum anomalous follies observing quantum coated with our magnetic field. Or also combining it with superconductors and freeze my arena. Fermions, fermions, fermions. And Anna Lewis is an analog to a neutral particle, but without mass, right? So recently I think we've been discovered a nutrient mass. But Mirena, me, it's, it's, I mean, it is kind of a mayor and a particle, right? That, but now there's wireframing. It's not that it's not a it's not a particle that you can findings outside the cell. It's actually a quasi particle that is formed with electrons. So that might enough particles has been predicted, that has been shown as the signatures, experimental signatures. They can exist in solids. So it has also been particular can be useful for quantum computing. So that way a lot of groups are working on getting made on a fermions, these topological insulators and superconductors of the political materials and superconductors. And there are other proposals were to use the polygon materials to like for example, using grading exit on condensates but x and I'm going to say it's based on the polygon materials. So I will go more into those details. But my main driving question here is, can we combat be trivial material or an insulator into a material without the possible, how can we do that? How can we, how can we created, Let's say, as I said, kind of like converting a piece of glass but now into the political material. Is there a way can we do, Can we do that? So it's one with the materials that we, we grow. It's actually these, we call them bent that these rates here, this interesting, it has been widely studied. It's a layer material. As I say, we can grow this in the lab. We grow, we grow crystals, something scotch tape decks for living and see layers of these materials. And it was already measure before. What I'm showing you here on the where my pointer is. If you look at this solid line, when they are measure, you can use resistance versus temperature. So 300 Kelvin room temperature. So UCLA went when they're used in temperature, the resistance increases and they got some pointed beaks and then goes down again. So you need reduces. So what is happening here? So they see that for the benefit of, this is actually was a weird temperature dependence because it's not typical. Ways are typically goes. Let me write down here industry. I mean, that would be yet with a bang. So whenever you have a metal so for, for riba has taking me, what happens when you cool down a metal? So a metal becomes less resistive. So the man-made it will behave like this. Ammeter will become less resistive when you are cooling it down because you're freezing or the finance in the middle. On the other hand, if you have an insulator, Let's say a piece of glass or silicon. If there's a, if the piece of glass us start with the same resistance at room temperature. And then if you cool it down, then the resistance will actually increase. Sorry, it will go something like this. It will never be going down. So what you see here on the, on the solid line, the black solid line is actually something mysterious because the resistance is not dropping all the time or is an increasing all the time, instead is actually peaking at some point. And that was actually very interesting and that was, there was a puzzle for awhile why there is a beginning assistant in this material. So the same for half a day, right? Is yes. There is also a big here, right? Around 5060 Kelvin. But for safeguarding and data write that B was around 100 Kelvin. So there's still, it was a password for some time. And then there were other theory papers seemed like Brady's Matthiae can meet the Polanyi felt, but it hasn't been shown that is topological actually. So he was highly Shang, if it's actually very Conducting is more like a metal, but he was never shown to be polite. So now let me show you the next line. But there were other measurements. So people has done, has a blind magnetic field. They have measured actually a very interesting more recently they have measure at 3D Quantum Hall Effect means all that. The whole effect when it actually means for the material is like they can, they can obtain crystals that are very high-quality, either qualities and good. You will never get the quantum Hall effect. So these materials can be granted a very high-quality in order to see what's the quantum Hall effect here. So these are steps that you are seeing in the, in the, in the blue car. These steps are actually the main signature for quantum hall effect. The steps and the dropping of the red car. So you see there is a step in blue when the red curve is 0. So that's the main signature for a wonderful software, these samples of Sarah quantum hall, that means that the quality of history, so it's pretty good. Okay. But so that's why we started growing these materials because we found like this resistance. It's actually interesting why there is a peak. It's not, it's not a metal. It's another nice leather. He doesn't behave like a military leader. And so we grow this crystal sizes you can see in figure a. So those are actually, they look like whiskers, like little needles, right? So we grow a bunch of those needles and my, my, my student or a postdoc can grab one of those needles, are measured their elected but Properties thus be so they measure the resistance as a function of temperature. And we also observe that the beating resistance, I will explain a bit more later. And then if you apply magnetic field, we can also see this, this resemblance of the quantum Hall will receive a step here in the blue car, I'm deepening the red curve. So we are also seen this 3D quantum hall effect in our sample. That means we can grow very high quality of the crystals. And when we measure a quantity called mobility, which actually encoding here in green, mobility, we are obtaining mobility for the samples under 2 million was, was, was centimeter squared per volt second. So what is actually this? This is telling us. We're getting extremely high-quality on these crystals. And even if we use a scotch tape to export them. This is actually when we see, you can see here these little purple purplish scenes on, on, on the substrate on Figure D. This little appropriately, properly, since I actually flakes of that decreased as that by using ascus today, we can break them apart and we can get very thing layers of those. So these are only 50 nanometers thick, is way thinner than a hair that you can have, right? There's only few items C. So we're going to actually these very thin layer, so half into the array on. So, yeah, as I mentioned, my lab, can we even how grandmother, other crystals of the stipple, of these kind of like the political attitudes. All right? But we were very puzzled about these resistance versus temperature peak. And we, as I say, we also measuring our increase those, right, and we get that. But what if actually that peak. So if we act, we do other measurements where we find out if is that unlike before, below that the action before the ethics of our temperature is larger than that. The mean, use the pointer for temperature that I blurrier than, than the resistance peak. So that will be for about 60 Kelvin or about 75 Kelvin. We actually obtain like they, like the sample behaves like it's actually dominated by holders, is kind of like the chemical potential. What I'm drawing here, what you're seeing on the, on the right side is kind of we have they, the conduction band and the valence band. And the dashed line actually represents where the chemical potential lease for high temperature where we seeing is that the chemical potential is on the site, the business, and on the bottom bun. And then when temperature starts to increase. Now, the fact that we're seeing is these increasing resistance is because that now the chemical potential is in the gap, is kind of a big behaving like an insulator because they're giving opposition is in the gap. But once they once, once it reached a peak, there assistant drops again, fan of being a metal. And we believe that is the it's actually, the distance is dropping like being a metal is now because the chemical potential is and the other one. So this has actually been corroborated by other experiment by rpois, not just by transfer only, but this also gives an explanation was what was going on here. That thereby cooling down these, the sample is changing itself and the chemical potential is moving from being on the home. Or it's moving from going from being on the Battambang to moving to be in the top man. That's very unusual for a material with a piece of silicon that will never happen because of, first of all, the gap is huge in silicon. So you will not being able to go from, from whole typed on electron type of silicon. But on these samples in that gap is mine. Yes. You know what, you guys what's happening when you're cooling down? Using what can be changing when you are cooling down. So what's, what's changing here is actually the lattice constant. So this is a crystal lattice constant, is shrinking when they're cooling down. Therefore, the chemical potential or the Fermi energy is changing when the lattice is shrinking. So my guess by jazz is temperature range from 300 Kelvin to very close to 0. The lattice is shrinking. And by shrinking that coming up, a denture is going from being on the leg on the whole site to be on the electron site. So that's very unusual and that's very interesting actually for a material like this that was corroborated by rpois. So rpois can look at the BUN stature. So before I was just drawing my bus structure by rpois can measure the bone structure of materials. So what you're seeing here on the, let me actually, let me use my thing. So what you're seeing here, let me use another color actually spread. So what you see here is actually the bottom one, as I was describing in my previous got them. So this is the conduction band, the valence band than sorry. So you're seeing the valence band at different temperatures. And the dashed line here represents the Fermi energy. So that's the same dashed line, but rather that I was showing you before. And what they see is like going from hundred, three hundred eighty five Kelvin, 50 Kelvin. If they see like there is kind of like the dashed line is moving now up. Or you could also think of like the Bond movie now. So now the dashed line is very close to the deep compared to what it was at high temperature. So by cooling down, the chemical potential is shifting from being on their site to the electron psi or going to the other one, then you can kind of see the other one so that Iran is actually here is another idea is hard to seeing artists. There's another one here. There's now the chemical potential is on the other one. By yes, by just using temperature. So then we were thinking, Okay, so this is interesting that just by cooling down. You are changing the chemical potential and kept changing the chemical potential is something that we always decide to doing in a device. Device we're always trying to use gates to change chemical potentials. But this material acid itself, just by cooling down because the lattice constants are in the same paper is written here. They also measure the lattice constant and they realize that lattice constant is shrinking with temperature. So the lattice constant is, it seems like the lattice constant is their main culprit for this, for this change in the chemical potential because the lattice constant shrinking at the same time, they show like the gap is also shrinking. The gap is changing. So I mentioned them in the gap is also changing. We will raise in temperature. So this is a very unusual, very unusual material that by temperature or by lattice, lattice constant shrinking the gap also shrinks and the chemical potential shifts. So we were thinking, how can we do then if we want to manipulate materials, right? If we want to create, went to make these muddy at the Polo, you gotta really want to make it insulating. Maybe this is actually an idea, Medea, because by changing the lattice constant, we could already modified the electrical properties of materials. But then how can we change the lattice constant of a material? So one way to change the lattice constant asexually by straining. So we found this paper in 2021 where they actually some theory work and then some experiments, some preliminary experiments where they say like initially these material is not, that is not a topological insulator is 10 of kind of metabolic and its leader without, without an E string. And they claim that if you strain the material, if you compress the material, that means applying a negative string. It can be comfortable item actually does. Barrymore seeing on this block here, this is the phase diagram with the claim that if you compress the material, you can go into these regime. That was a region of interest. This part I'm just highlighting there where where probably an STI, STI means a stronger polygon insulator can be formed. We're thinking maybe that's a good idea. So we should try to the compressor or are actually a strain the material in order to reach to this, It's Toronto polygon insulator. So we would train that we were. The first thing we need is actually we glue pieces of our material on top of a piezoelectric. Piezoelectric is, it's somebody you know that if you apply a voltage, it actually compress or the expense. So we glue our sample, we blew it using a boxy into these piezoelectric stack. And we're going to apply a voltage and the pia selective stack, making the best of it respect to compress or expand under the same time when the deselected compress or expand, it also compress or expand our samples. And what we found is actually a low temperatures. I mean, you're seeing here in this plot actually that we can actually change the resistance of our samples. That the army, the change of resistance and are not means that resistance without any string apply. So we can actually see that there is that large change of resistance when we apply a strain. So the x-axis here is a string. It's a very small amount of the strain that we don't blame. The strings are playing on their, on the beer selecting styles I mentioning. But that's enough for our assistant, for the sample of our resistance to be changing a lot. So it's changing more than an order of magnitude by yes, are playing a smaller one in the string. So actually this is, this is a way to, to compare these curves is by, by comparing these GEF. Yes, Actually, Jeff is called the gauge factor. The gauge factor is a comparison between the amount of resistance change with the amount of a string apply. So we found our sample that we can get these factors in the order of 2000, or even some of those samples would have found a gage factor in there of 10 thousand. So we can change the resistance, especially a low temperature. We can change our lives because of our samples by several orders of magnitude. By applying a very small amount of a string, we're playing less than. So the string quote here is 10 to minus four. So that means it's 0.05%. So it's a very small amount of the strain of airplane. And we're seeing a very large change in resistance into something. And it will look into comparing with other samples. Or low temperature, at least the amount of obese factor that we measuring having to race is huge. And it's only comparable to silicon nanowire. Unfortunately, silicone nanowires data is only at room temperature. So we have found other materials that are low temperatures can be changed by this much. So that was already for us interesting. So these materials is promising, like by playing a small amount of strain, right? Bye, bye. Bye, bye. Massively. Trained by straining by a map at least some amount of positive strain, the resistance changes a lot. It can be is kind of like if it's more assistive is now more enslaving of it over these less resistive is more connected. So it's kind of making a piece of glass, making converting more into a piece of gold, right? Because it's more conductive, that sense. So that's why these materials is for us very interesting. But then we realized like by using that gets us that we cannot up by that much a string. And we mount, we create a new. This is a home-built bending station. So now instead of buying a string, B-A-S-S. When we're doing is actually we're bending a piece of metal. This is, this B here is actually titanium. And we mount our sample of titanium and we bend that piece of titanium. And where we then du piece of titanium. Also our sample is being strain. And we have Sarah thereby you're straining that our sample and we measure the resistance of our sample. Actually, we obtain something that seems centers. So without any string does the black curve here and on the right. So whether I'm plotting here, this is resistance, resistance versus temperature, electrical resistivity. So he's converted, corrected with the units of lens. So resistivity versus temperature, initially without any string. Well, wheelchair is the same thing that we were observing before. Initially the resistance drops, they need increase and erases speak. So that's the blacker, right? And then it drops again. So you're reading, explaining what's happening here is I, we're getting some electron transport. That's it. But then once we start applying a string, let's say 0.26%.96 of a string, or 2.2% of a stream, or 4% of a string. Now the resistance versus temperature start to be tending more dramatically. And when we are applying a 4% of a string, now the peak is kind of gone. The peak of resistance is almost gone. But we're seeing like mainly the resistance is increasing with reducing temperature. So now this is more behaving closer, gametes later, as I mentioned before. So I need to later the resistance, yes, increases we reducing temperature. But there is these plateaus. Sorry. I didn't weighted in my opinion work there. But a low temperature there was this interesting plateau. So they'll start to plateau at low temperature. And actually that's one of the, the saturation of resistance is really one of the signatures of being topological of, is one of the signatures of having actually at the bottom surface states. So why are we, why do we why did we leave that? Now we're grieving this tuple lake surface stays in having direct. So I'll show you that in the next and the next night. What we believe is happening. It's actually initially right for, for high-temperature we, our transport is mainly dominated by holes and a low temperature has made them and electrons. And where we live is, believe is happening is now with a string. Let me use, let me actually show the plots here. So without any a string, if the chemical potential is going from me on the on the bottom line to go to the top but but yes. But yes, cooling down, right? That's what we believe, the same thing that happened before with our NSString. But now once we are a string, this sample is now like weird chain the gaps. So the gap is getting larger because it's somebody's being a string. And at the same time now the chemical potential cannot reach the other band because the gap is now larger, because we have a string, the sample. So by E3 the sample, we can only go from being on the bottom band to being on the gap. So therefore, if that's what's going on, then we will never being able to get that other metallic regime again as well we see without any string. And I think that, that's what's happening with our sample ones. They come up a string. That's what's happening when we look at the temperature dependence of the resistance of our sample with a string. So, but then what happens when the chemical potential now is in the gap? Why are we seeing actually a resistance being in there? That means that now should be actually isolating. It shouldn't be plateauing, like what we see here for for us. I see my pointer is freezing. Can you guys hear me? We can hear you. Yeah. Your pointer is there, but it's it's now moving. So moving, yeah, I always use is frozen. I can't even moving now. Okay. It's moving. It move just now. You have some irrational other way. Yeah. Yeah. I'd say it's not moving in erratic way. Correct. I kinda I cannot control it earlier. Okay. Suffers a reason, but maybe I can entertain. Your pen was Babur now using annotation. Okay. Well I want to point out what actually is this area where so Assist I'm saying here that give me that potentially is in the gap, but we're seeing some resistant plateauing. That's very unusual because he is a chemical potential is in the gap. There. Should be large, should we keep going up? No, just put a point there. So that's actually something interesting. Then we start to wonder what's going on there. What will I already give you a hint that these might be actually a signature of the topology or surface states. So then the next thing that we did, it's actually trying to go to the next line. So the next thing that we did is applied magnetic field. So every time that you have at the polygon material, everytime you have a material that has high-quality, you want to play magnetic field. And the magnetic field that we apply, it's actually the other thing, magnetic field because we wanted to see what to look for these quantum effect that we were seeing before, even without any string. And that's actually corroborated without any string, we seek 12, why we see these oscillations in resistance of the magnetic field. And even up by applying a string, we still see this oscillations. The oscillations are still there giving a 2% of a string, given at 4%. But for some reason the data was, was not as good quality or these are the, and then something has happened in the sample. But we still see the oscillations giving a high strength. But as I mentioned, even when we're playing high a string, the chemical potential now it's not if it's in the gap. So a day God, you shouldn't be seeing any oscillations. Because these oscillations are actually the, the forum because we're seeing as a Fermi surface. But there isn't a Fermi surface in the gap. And the gap there, It's not nothing. There shouldn't be any oscillations. So our interpretation is now that the recent way we're observing this oscillation is because we're seeing actually the surface states, that geopolitical surface states when we're applying a string. And my post-doc did something else actually then he started playing magnetic field in a different direction. Because that was actually something interesting too. So if he, when we started play magnetic field, that is the sexually in line or parallel to the y direction. Initially without any string, we see oscillations as, as typically we always see for our crystals. But once he started, players are playing a string, the oscillations are gone. So this is even for, for highest string, you see these linear resistance with magnetic field. There are no oscillations there. So if we take a Fourier transform, if we take a derivative here, we see no oscillations on the, on the, on the hi string. So this is now more in line of what I mentioned about the book. So we are, we're a gap in the bowl. So therefore we kill the oscillations when the magnetic field is seen in plane. By when the magnetic field is out of plane, we still see oscillations because there is a topological surface states that have form when we open the gap by applying a string. So we got the ball, but they're, they're still very conducting surface states that are giving us these oscillations as shown in the previous slide, that there are giving us this oscillation. And the same thing is giving us these plateaus in resistance. There are some, some state and I did that happen. Linear energy momentum dispersion that are filling the gap that, that wasn't there before, before we apply a string. Or maybe we just, we were not being able to see them before we play string. But now by applying a string, we can see this this surface state that is very conducting and they still shows this oscillations. And these oscillations are, they can only form when you have something that's very conducting a very high-quality as well. So this is, this, this is a signature that we're creating, that we're making haven't there right now being anthropological material. So before we apply any string, it was not at the polygon material, or simply the chemical potential wasn't the right position. But by applying a string, now it has become topologically. So what we're seeing here is that the political face transition by applying a string on the material. So a string can do this. It can, it can. Now what we are observing actually one of the facets of a thing, It's actually can convert a trivial material into the polygon material. And we're excited for that because we're thinking, what else can we now make it topological, right? Can we convert Celsius is relating to metallic, copper, metal tongue insulating, though don't easily later by supplying a string. So my group has started to working more of these strain related experiments. So after you defer different strain cells to be a large amount of a string in our materials. So these are homemade, guess electric constraints are that we can apply. I mean, this can actually be the place for, for large distance 10 to minus 10 to 10 millimeters, or actually has two micrometers millimeters too much. We have also bought this commercial straight cells, and this is the bending station that I mentioned that we can bend samples and we can create a string or something. Actually these bending steady s2, s2, because it's not like we can only create uni-axial string by, by many we can create a string radians. So a string grains are interesting because they can also create some sort of the magnetic field in quantum materials. And where we're really looking forward to see proceed or sort of like Sudan magnetic fields now and buy the materials by applying these, by bending them instead of just a stream by bending them. So we were also trying to study those effects are what the material. And now also we were also looking into what happens with very seen flakes. So half into the array seems to be a very interesting modality. The best allow them the amount of the strain that you can apply to it. So in my lab we have, we have built, we have actually a transfer station inside the glove box. So we can make these bundles that the restructuring, very controllable environment, my Osiris and being able to create actually or transfer flakes on the right in, in cariogenic, modernized starts rusty. So we can, we can do this or very low temperatures minus 120 C to protect the flakes because it's flakes are sensitive. So we can't grade devices out of the scene flakes apart. And Thursday, am I, since I've actually measure very interesting electrical properties on the skin flakes. So. This is actually the SYN flag and the boat. They all have these kind of like Beacon resistance, as I was mentioning before. Um, but they seem flakes have something that is very interesting. They're resistant, they're actually the, show these anomalous Hall effect. So anomalous Hall effect is when you see on the blue curve, where do you see a very large jump in resistance at 0 magnetic field. So it can drop from being negative to positive with a very small magnetic field applied. So this anomalous Hall Effect jump. It's, it's actually difficult for, for a forum for magnetic materials, not for hadn't covered arrays, not magnetic. But it's actually behaving like if some magnetic material. Because having to re, has actually a bay large g factor. Therefore by Yasser playing as more magnetic field, we're going to steam boiler eyes, the bands. And that's actually the reason why we see these large animals for the thing. So when we compare, when we compared the anomalous whole angle for, for having a particular materials. So we see like their nominates, her language, which is Yasser, the novelists, her language, what it measures is how much anomalous all resistances in your sample compared to the normal, normal, normal phone. So we see like adenoma is huge, is more, is around 100 percenters. It can be very large or very large factoring in the, in our samples. So the reason why we say, well, we will leave, It's happening is that we have as being polarized, polarized bonds that us, as we're learning from the string measurements, it could also be yes, coming from the surface states instead of just the ball. And then they can also help to have a spin polarized bonds. And therefore, that could be the reason why we're seeing these and these large abnormal, it's called effecting in the scene flicks do. So, right? I think we're running out of time. Maybe what I want to have is questions. So let me go to to actually Day familiar slicer. Let me is when I go to their conclusions and thoroughly, if you guys haven't yet, no, it hasn't yet. So you guys have any questions? Because I want to add a missing data. So feel free to continue, to just continue finish up whatever you wanted to say. Alright, great. Yes, because then the other part, I mean, this is mainly focus on the electrical properties, but the other part of my, my lab, what we do is actually we focus on the optical properties of materials. Oops. It went back to the main slide. Sorry. I see whether you can write, because the other part of my group flippers in the optical properties. And these two, the Medea sanctuary, very interesting for, for optical property still, because I was already describing whether semiconductor is where you have these two bonds. And whenever you shine light onto semiconductors, you can create these particles that are formed when an electron from one been moves to the Durban. And this electron under hood they left behind concretes. These particular calling exit done, which actually is usually shorter leaf. But we can do experiment with these particles. We have done experiments. We have usually these are short-lived. They are only two picoseconds in like lonely. So it's very short because seconds to 10 to the minus 12. So it's very hard to learn. Experiments with particles are the only live for these short amount of time. So weaving able to actually increase the lifetime by putting together two different layers. And then the lifetime can be increased two orders of magnitude, two microseconds, in that case, too few microseconds. And with microseconds there is more than you can do is you can control there movement and you can actually manipulate them. And that is what do we have, what my lab is trying. So with this sort of exit zones, these are delayed accidents. We can get long life science in microseconds and they're encoding nanosecond, but we can do the microseconds down. And that's actually something it's available in to the materials because you can put one layer on top, on top of another one and create these new capital structure. We have a lifetime. And what's exciting about accidentally delete materials if the binding energy, so the binding energy is the energy that they need in order to form or the same entity that they needed to be broken apart, these electron-hole pair. And he taught us, I would like for that to the materials binding energies in the order of 300 mean electron was compared to both 3D semiconductors is only other thing, millielectron volts. So it's very hard to do any R or to use these oxytocin, the 3D bulk semiconductor because they have a very short lifetime and they have a very small binding energy compared to the 2D materials have large binding energy. So exit dosing. The Mathias actually can have very exotic physics. They can, you can, you can create Bose-Einstein condensates, or you can actually create. Also look into this. This is a phase diagram of how they in the late access to the materials will look like. And the interesting part here is this red triangle area where the Bose-Einstein condensate has been actually predicted. There is some signatures that are instrumental signatures are that happens on this sort of Materials. And this is only available thanks to this. The, to the nature of these materials. Did you cannot get these phase diagrams and other semiconductors. We can pay with that 3D semiconductor, let's say rebelling arsenite. The phase diagram will only be on these really tiny red triangle that I have drawn on the, on the left. While the 2D semiconductors gave us, are enabled us to explore this condensation even higher temperatures are higher densities that was not available before in other systems. And why do we care? Well, was that both sounds like condensates go well, because they could be important for creating quantum simulators. Went to simulators are only available in cold atoms. So Mark I remember Mark work with the cold atoms do before, right? So cold atoms are, are, are, are quantum simulator and columnist and commuter life, but they require very expensive equipment and very extensive experiments that are very, very expensive too. Well, what I'm proposing here is we're using the exit, don't seem to do the materials. We can use them to simulator and yes, use we can use acoustic waves to actually localize them or move them around. That's what the other part of my lab is doing. But I don't sing, I will have more time for that. I guess. I want to leave it there. This is some of the actually, oops. Again. I want to leave it there. By, I want to say thank you and I will give you a summary here. For some reason it gets back to let me bring you here. Yes. So I just wanted to show you like I showed you, we can grow high-quality crystals, have these giant gauge factor, you have IntelliJ, right? I've seen singers but the polygon face transition under a string on these materials. And we have hedonic paradigms. So you might have actually being able to manipulate exit dumps into the materials I'm using acoustic waste. And so this is my group. My group is her boss or what was that we have progressed is and undergrad students who were very excited and working on quantum science system. So you have any questions, please. Thank you. Thank you, Louis, Let's say Robert Louis. Thanks a lot for this february. A very clear, very interesting talk. So, yeah. Any question from the audience? Now have a comma representing each other. No, I don't see in the chat. Okay. Well, if well, I always start with a question. So is it right that the tape your flake off, you're happy and material than you could also gate it could turn the chemical potential. So to bring it in and out of the topological phase with that, Would that be correct? Yes. This is what we wanted to. Okay. Got that. There's a problem with that because sodium, but they're very sensitive. That's why we have developed these other way to to to do dinner any transfers. So now we were able to, to, to, to put boron nitrogen top and bottom. But unfortunately, since this is still very conducting, giving an electric field is a bit hard to apply. So what we have to at least seen that we have done is actually use liquid gate. So we liquid again, we are able to do that too. Okay? All right, so liquid gaze another way, but we're really trying to get into the single layer case where we can apply just an electric field. So that would be the best-case scenario, right? And then we don't need to use a strain per se, right? Or maybe we can do a combination of a string and engaging, right? Yeah. Yeah. Any other question? Any yeah. If anyone else would like to ask some question. I mean, I I can keep on going better. Wish you that the audience have a chance as well. It won't then let me, okay, let me ask one more question and let's see, maybe the audience need a bit of time. Wow, so actually what is this cryogenic PDMS transfer? What is, so why is, how is it different from the conventional PDMS transfer or how is it better? So, you know, with we use the cryogenic, the chorionic be, the mass transfer is because actually PDMS is very sticky and low temperature. So with PDMS, you can actually sample some PDMS. Yeah. But you cannot use PDMS to pick up where we use PDMS, yes. To to write data flake and then place it somewhere else. Or can you can pick up, right? Yes. But in order to make PDMS to me was to pick up PDMS is very sticky when it reaches minus 90, minus a 100, see, okay, it goes through song transition temperature, then we can pick up materials. Okay, I see. And you want to use rather than PC because PDMS just easier is that the main logic is for BC, you need to go to 200 CE. I am going to 200. See that the sample variance destroyed, right? Okay. Damage, Yeah, him and less heating up by cooling down the sample doesn't get damaged. Yeah. Okay. That's the reason we want to cool down the sample. Yeah, That's very cool. Okay. Well, does the audio have any question? Last call? Actually, I have a question. I'm going to show us how how is the bending of that using the bending institution got transferring through their flick? Unless I finished my sentence. That's the real question, right? So we're bending there. Were bending a piece of, is it actually a beam of titanium. And the sample is stuck to the being of titanium by, by using a boxing. So we use a non-conductive epoxy layer in between the beam and the sample. So they've definitely stay him on a boat is actually there. That will be the upper bound because we're playing is that amount of a string is only a tiny beam, but the sample is less of that. This thing is going to be transferring sample because some of that is going to go to the boxing. And that is a layer material. So a later material also, most of the string is probably on the bottom layer. We're on the top layers, right? And actually, the main idea I mentioned, but the main benefit of using layer materials is like the layers can slide when we're playing a string. So therefore, it is easier to buy larger string on these Medea as compared to, let's say a piece of silicon. And you try to bend a piece of silicon, you will break it into pieces, right? Because it's 3D and it doesn't take that much extinct to break it. But the layer materials are more flexible in that sense. But that's a great question. Very nice. Any, Any last question from the audience? Plug in. If not, then let's just yelled everyone, give it a pause to a Louis again. Thanks a lot for being with us too, to tell us about your work. And we look forward to hearing about about an exciting result coming out of your lap. So gases, and thanks everyone for coming. And then I will just end the point estimate here to do the courses. I mentioned that before this mean.
Colloquium: Manipulating the Electrical and Optical Properties of Van der Waals Quantum Materials by Static and Dynamic Strain | Luis A Jauregui, May 11, 2022
From Federica Bianco May 11, 2022
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Topological order and materials have been at the center of attention in condensed matter physics
and engineering. Topological materials, a new quantum state of matter, are a family of quantum
materials with boundary states whose physical properties are robust against disorder. Therefore,
there have been few examples for a topological phase transition realized experimentally, even
fewer cases for an in-situ tuning of the topological phase. For the first part of my talk, I will
discuss our results and methods to apply uniaxial strain in topological van der Waals quantum
materials and how it influences its electrical properties. Our results point towards a topological
phase transition of the system tuned by in situ uniaxial strain. For the second part of my talk, I
will discuss our approach to creating dynamic strain in van der Waals quantum materials and
how to control the electron and excitons dynamics in such systems. Our results could pave the
way for creating topological phases of matter by strain engineering in quantum materials and
devices as well as a step towards a solid-state quantum simulator platform.
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