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>> The speaker was relaxed graduate work master's degree physical problems and as you know that is Ph D. in university postdoc at U.C. Berkeley School of Business here was his research interest. You know what varied including study and transport always. We're hearing what he has told us today.

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And we want to go anywhere. Thank you thank you for the introduction and thank you for being the patient it's a great pleasure to be in this building. Even though I am not a very frequent guest in this building by my students saw they utilize the Micra the clean room very frequently and well looking forwards to the opening they'll feel L'Arche now and take facilitated this will definitely boost my research.

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All right so it seems like I'm from the school of physics. Even though the title is probably just one technological application so superconducting Munna Why do you write so spleens for need me. It will be more about proper test but I will mention how a recent discovery this and rediscover is so cross some unknown phenomena actually lead into hopefully very very interesting technological applications maybe knowing your spew church.

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Now this stock will contain a joint award between my group I lead the group and they are just two great good students who where there wrecking the wealth in this resurgent who is now a pause at the University of Illinois and random who is going to be the right.

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And hopefully very soon. Based on the results of this work for explanation of experimental results we had to work and that was a pleasure to collaborate with a group of professor who was the Lamb who performed first principle in the medical simulation structure and transport and as we go I will explain you exactly would you Will it and how it was done.

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The funding was provided by Georgia Tech through my startup mostly and Assef. And Department of Energy and again thank you for inviting me now here is the outline of my talk. So basically I will start by explaining how non the wires out and then the wires and the methods that I am going to describe are going to be suitable for our creating a very thin metallic on the rioters.

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But if you're interested in studying molecular conductors this methods applicable as well I'll tell you about behavior and behavior. I mean unusual property is that the region lead from the fact that we study in basically a system which is just a few atoms and sized for quantum effects of a large importance.

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The next part will be real to to the superconductivity in these small objects and it will share knowledge that superconductivity would be essential for us to provide sufficient information for us through numerical calculations through the store the atomic structure of men the wires. I'll tell you exactly what needs to be involved in the ballot or the method so involved and finally I will tell you without what we discovered and this was a recent publication in The Nature Nanotechnology is that so.

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But on the T.V. has a very specific we wrecked in way a small object small amount of wire sympathy killer found that it was. Specific superconductivity that you can the side and the Tet atomic scale mechanical motion and just to give you up front. Some information loose vibration frequencies are in the terahertz range between.

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Ron and down their heads. OK so let's move on. So here is. What do I do in essentially upwind context this is all experimental methods on this slide simply gives you a couple of very famous point conflicts even though the younger part of this audience but when I was a kid which was not too long ago.

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I still and I still like playing. That's why I'm out of experimental physicist right because this kind of radio the future lies this so-called get scatter that that this was a very very popular thing you basically had to have a very sharp metallic wire and find a sweet spot of it in the crystal and then you could listen some radio.

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I got behind the Iron Curtain and one of the things that you could do is actually peek up the works of American radio station that's now and I'm allowed to say that but this was part of part of the support. Now this is of course another very famous point com that this is the first semiconductor introducer heater.

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If you recall the story was wrapped around the point that slide by razor it provided the very sure it path for the R. and the bend pressed into into a semiconductor to provide the very short. I needed to collect a distance and that is the gain if that was realized for the first time.

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Now we moved a little bit further. There is the case we as I promised and as I mentioned we made contacts which are just a few atoms in size. So probably you this sort of prediction and then the prediction for the method of this method was done. Numerically by a group of professors when it was in lamb here and.

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Georgia Tech very soon after the technique which is now called scanning tunneling microscope he and the Democrats McCroskey were discovered. So basically the simulation here show was a nickel tape and it was one of the first much it also it's a hard metal do you into a gold surface of gold.

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Here is depicted by this this layer of structure colors all different layers. I just the guy for not I. To tell you the fellow and when you drive this deep into the surface it's been my great on may kill or any other material it migrates even not from the surface but a problem for a moderator so you can see green and yellow and blue Adams moving up and then when you try to remove from the surface it will actually put some of the metal with it and form this this nano wires.

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Now if you take a close and professional women's group you go through a numerical simulation is about that said recently been done by the you by use in a very high power transmission like the microscopy you will see that actually the structure of this then the wire says nearly perfect.

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So in the case when you pool when you crush a goalkeeper into a gold surface strands of gold strands of gold atoms are proof. And if you pull from the sample you will see that you start with that five strands then you move just a little bit. You have all three Ron and then Nanda confident breaks in becomes a tunneling context.

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It actually has a very easy explanation defect costs just a lot of energy to be incorporated right. Structures and small and small size tend to be perfect. You can. This is this is something which will be very important what I'm going to say in this talk. All right so when you move.

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This technique which is the scandal in town and. I'm sorry that is. The technical skill entirely microscope is used in physics for what's called skin tone and spectroscopy. So basically with their skin tunneling microscope you can not only image of surface and this is what is shown down there but you can also study the density of states all electrons to what they are by the charge carriers you have by bringing the keep close to the surface you can sweep the British measure the current and this will tell you the levels or energy bands electrons can take.

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So the most spectacular probably. Pictures come from high temperature superconductivity this is still in the open question. This is where the S.T.S. because it is very is shown maybe some possible make and use them. So for the nature of the superconductivity. However it will lead to technique which is called the point going to expect rest could be as well.

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So for a lot of interest. So again as a reminder S.T.S. are sensitive to the electron density state when going to expect rescued this is when you do drive the surface deep into the surface and have a very small contact is actually sensitive to the interaction between conducting electrons and the cause of the articles for instance forms.

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The principle is shown here. So when you have a very sharp teeth. Most of the real bitch that your bias your likeness with will be concentrated in this area right in the area of the point content then if this energy is high enough and the electron can meet the form of this is going to be do stupid process and there is a chance that this film can backfire back into the point that interact with not the electron and the like to not be able to pin you trace through the clump it will go backwards.

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Therefore you have the suppression of combatants by doing. Aeration of. OK So it turns out that for both of these methods mathematics can work out so that you indeed have either elect them density of states with or elect in the form and direction Specter this is very powerful method which is complementary to such a large scale.

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As neutron and X. rays scatter. All right so now it works. All right so we use a little bit different readers a little bit different technique we use a technique which is called microphone brigade to break junctions and the idea is shown in this light so basically you start with a flexible substrate the knowledge case this is hard for me to think for Suppose Braun's you speak of very thin layer when the insulator probably a mind to now case the thickness of my crime fake and on top of that.

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Well that might later you macro Febreze Kate weakly. So this is a structure this is a zoom if this structure we have two contacts which are initially fabricated so they are connected through a suspended breech which is a biology hundred ninety meters in length hundred in the meters in diameter and the suspension here is probably a ball at the micro So if you're interested in the how this is fabricated.

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We are ready to give this recipe Olic right about to publish publish a paper all this work is done in Georgia Tech or in this context of fabricating Georgia Tech some processes on the network in particular rectify a mansion and optical your therapy. Unfortunately up till very recently and still the case since what used to do with our own facility in the school physics which I co-founded with Professor to do each and also unfortunately do positional somewhat uro's like niobium require very.

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Supect you need such a spluttering and materials like my old women tend to loom they're very sensitive to minor minute concentrations of what you're there for we had to build a special spattering operators which has a cryogenically cooled screen inside that only after this was done we were able to achieve superconductivity in this material.

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So this technique works as follows sort of a typical cheap is about and mean chain length. Right. You basically have three point supports so you'll be a whole B.M.'s. If there's cheap and then we bend it from the wall right so when you do this. The structure on top of the glued well to the program.

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Mike will break at this weakest point. Now the advantage of this method is a big ration mechanical attenuation ratio of this to me because you transfer basically motion vertical motion into pull him through bending. And in the case of even the very simple technique when you have a notch to wire so you can take a big wire cut that through almost and bend that you can already have in the nation overbroad one two hundred in our case we have an intimidation in excess.

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So we want to turn to it if if. Sometimes it's wrong to add to the milling which allows us to manipulate the length of the constant over the P. commuter is an additional. Right. So this is very sensitive we can control the separation and what happens in these three regions with very high very high precision.

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Now on top of that since I told you that this insulation layer is one micron in size some of you can may recognize that this is actually microstrip circuit right. And therefore we can actually create more sophisticated circuits that contain the brake junction as a part of this circuit so far.

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Great to be cheated and was actually that we have created a very nice field there so you can create. Very nice distributed. And while. Filtering against radiation against frequencies in excess of about one gigahertz So this is very important for us. You realize that we have objects that work without just a few items in size.

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So we have to take care of noise to the highest degree possible. All right so measurements are what we do we measure basically current characteristics and differential conduct themselves a function of the voltage the and the try to realize what happens just from those measurements This is our type of doing spectroscopy.

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Now just as a reminder maybe the differential conductance measurements conductance is the universe if there is a distance R. done directly by a simulation you can meet the advantage of looking differential conduct and see when the most actually theory is work with current real push characteristics is that emphasizes not in your edges in contexts right there where you need structures change in the slope and the current British characteristic will result in the step in the differential conductance and the step in there and the converse characteristic will result in the peak.

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So these three chairs become That's much more recognisable in cars. All right so now the promised quantum part tried to be with me for the last explanation of what's happened this doesn't require that all right so when you talk about whether you should take into account quantum effects in electronic transport you have to deal.

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You have to compare basically three rankes the length scales with China very often the problem. Wrong lens scale is the smallest size of the device and in our case this would be a non The Wire and not object which is longer wrong and things to do. Rise is going to be the smallest size.

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The second is the so-called care their length and this is where quantum mechanics comes in. Even though electrons are the also waves. In the physics right used to that and we use this things and then change a B whenever it's convenient. We say electrons are particles when they were as can being with say it's waves.

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So I'm apologizing when you talk. I'll start mixing things up ask me by the way this is the imitation of something that is unclear. Please ask me all I am happy to answer any questions during during that time. But anyways so this is one of the fundamental principles of quantum mechanics right this is how it started it was discovered that particles elementary particles electrons in particular get me wrong with ask it as particles and waves and electrons you can assign a certain great length which is associated with that.

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So this is the circle for me length. It is related to the energy of electrons through a simple formula and for election to normal metals This is about and then throw my few extras so it's about atomic size which again is if you think this is kind of nature we know that atoms electrons and that themselves quantized orbits right.

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So right. So it's the wavelength of the wreck and when it becomes comparable to the size of the object. This is when quantum effects dominate. OK so we used to have to be comparable. Now when you study real systems and you want to study electronic transport you should also ask yourself whether you electrons are going to be interacting with anything even the conductor and there are people interaction processes that make him a car or an electron can change in some amount them.

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That is it can hit something and be deflected from its initial path without losing the energy and this is the. Drastic step train. However electro chemical so lose some energy. So it can keep something transfer and then energy like into the phone says I already mentioned the right change the energy and the direction in this is going to be.

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In the rustic scattering OK So I think it's apparent that the easiest case is when you compete can be glad to escape through Also system discover just the situation when there is no skittering at all. Bot the root of the rise is about the throw me away flank and you have to take into account quantum phenomena.

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All right so theory can be anything to be very complicated but this is that Admiral has a simple explanation of what happens. So what happens is the full run in the electron enters this area. It can not take an arbitrary energy right it has to take and then a G. which has a quantized component right here these quantized component depends on the.

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The energy of this level depends on the weight of the earth and that all right. And the only that was selected is that have and they're just so that their continuous part plus the current price for add up to a certain value can pass through the construction. All right.

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So in terms of the energy diagrams this is what happens you have two charges the Iraq and the rectums because these both in letters that are in the right of Israel rather you have a page bias here it's more commonly I would smoke in the physics route that she is really to the chemical potential So the chemical the means that the chemical potential source of the story is that a writers are different and what you have to do not know is you have to move in the right from running to to water and doing neither right.

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The electron that is have to come from the reduce or is there water jump into one of this levels and go into the other level without that is there water. There is a process that will supposable nothing prevents an election. From here jump on to here and come into the left as it was right.

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However the net current would be only due to those levels which odd between those two chemicals but the actual. Think about that. And a let down when the jumps here right. What it sees it sees that there is a level on the right hand side which is a milky white so it wants to move to the right hand side but he doesn't want to go here because the level of the occupied.

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OK So this is an umbrella and situation only in this region. Now the next thing is to notice and I will not explain that in in my detail but I'll just tell you that for an ideal quote that the context of this shape and this is sort of stuck up in the idea bet you contact the conflict which is shaved so that any electron which moves from the left to the right will actually end up in the air and ballance through that you'll find that there are side channel or such level there is a finite resistance and there is actually not small.

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It's about thirteen Q Were there such channels you can not make the resistance of one channel smaller This is a fundamental. Restriction on electronic transfer through quantized levels. OK. All right so the total current however would be determined by the chemical potential difference because as you increase the voltage right.

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You are before the transport and that is the current is going to go proportional. Alright so in this situation we realized the answer is yes we must be particular demonstration and the first demonstration effect through this picture was done in two in the dimensional gas so the problem know that you can fabricate or like them gas which is confined in a two dimensional way are several meters below the surface right.

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So it turns. That in would use dimensional systems to great lengths of electrons so what they were the charge here is there is not an atomic size. This is the departure of material as well and it turns out that that great flank there is several tens of meters.

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So the Fall Into can you can because then developed its so-called electricity to Gayton right. And in this case a bop the the two dimensional plane gas people fabricated to who was Gates right in the best shape and applied but down show high enough so that electrons were pushed from underneath the gate electrodes is actually from me to those gates electrons.

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So if you increase the potential you can as a matter of fact make this or this or this point. Some or a larger and people were able to actually sweet little was conductance channel wrong. One by one. So in this picture of these dates back to one thousand nine hundred ten years ago.

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You can see those channels where switched one by one and actually they were quantized exactly in these units in the units of universe or thirteen the killings at some point it was even considered to be a standard or there were resistance by the National and sort of stand us in technology but then quantum Hall effect provided much better and more a Bost measurement of if there is the spirit to be quantum here and provides you with your five point six kilograms.

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All right now this is an ideal situation. However rather scroll to the next step and the next step will be to chart on a rustic scattering. OK so in the picture. Do we have we have this problem picture we have the left the right is there water connected by a few channels.

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Now we assume however that in the film can be scattered without changing that's OK so here I see. On my particle duality I'm saying that and the electron is a particle. Right. So I move with discrete charge from the raft. To the right. However when I want to describe the transport I want to consider it as a wave.

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This is one of the powerful methods implant the mechanics because an electron can be considered as a race like it right and this way fake it can be constructed from plane waves. OK so let's play in waves. They scatter. Generally speaking independently on their way vector and I can conceive of just one plane wave right in this kind of situation and then I'd say the electron the is the is a combination of clothes plane wave so what.

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There was one way is going the good good for the whole lot. OK So this is what is going to happen. The mechanic is probabilistic right so even though the electron usually occupied a certain channel in principle you have to take into account that unlocked and can be transmitted through not only the same channel but it can also be scattered into any of the available channels and become better but it can also be joined back wards.

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All right so it can either go through a group backwards at this moment we don't care about the mechanism this is our fandom in the model what we can do what we can collect those transmission probabilities were deflection probably just whatever you choose there related into mattresses. OK So this is very similar.

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If you took elementary quantum mechanics this is a very simple scattering theory I think in the like a magnetism you have something like that as well in a bit different form. OK this is the formula will calculate in the total current and even though it looks pretty maybe intimidatingly it is not the case.

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Generally speaking the formula contains the information about transmission coefficients in this matter actually it's a Trace right up this metrics and then you have the information about your electrodes and those. Two functions this is the study electron density of state and you see that as a matter of fact again the total current is proportional to basically the difference in the density of states in the in the two it is their waters and there is also some information about your conduct and call it.

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All right. So this problem can actually be reduced. Again seems we used to play in waves through the system or tell you that plane waves make America a nice basis which you can die again a lot of sin. You're not there. In other words so you can actually reduce this problem to the fall and step up this channel mix in which you observe.

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Right. By changing the weights a little bit just a mathematical description of the problem you can mend up with a set of independent channels. OK you can say that and start in the south and channel it ended up in the same channel and this is the the new formula for that situation which contains simply what are called transmission coefficients.

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OK So this is the mode of the you in the going back comes and one of you in the conductance is the forward. If you start with a very small object you have a few combativeness channels. When you increase the size of the object you actually increase just the number of channels the channels and up and peril at UP IN PERIL.

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So the conductance is set up in parallel. So the object becomes more and more conductive right. Of course at some point when the conductor is very large quantum mechanics in the applicable channels lose the caret described value and then you have to go to continue mechanics but we will be working in this approximation when we have to take conducts channels and it comes out right now metallic nano wires what happens.

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What happens when I was in the fall and this is we are going back to the station with a good point where you saw you can actually make the wires which can train contained strands of growth of atoms the record now I think is the chain of gold atoms which is eight at.

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As long as we can actually prove anything. The chains bought it's a matter of mechanical stability. It's just just very very very difficult. You have to take great care about the buy brace inaugurations because this would be the use that these objects break very easily. All right so let's see even the conductance is quantized in exact units in this case.

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Well for gold and this is again wrong of this record experiments where people could actually observe those trends simultaneous it with conduct and never meant you can see that trans become that and then the wires is that actually quantized in the units all twelve conducts quantum which is when you have a run strand you have one quantum two strands have two quanta but that's about it.

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You can football with its chemical simple chemical nature. It's and they have smashed always has a spherical shell right. If you have more than two strands you will not have exact inductance quantum So when you go to materials like niobium and this is about right. Interested in this situation even worse.

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So this is a typical experiment that we have when we make our contacts with the mechanical control brake junction technique and just as that in mind there. I don't have five million dollars and it's mission like that on the microscope with a cryogenic stage. So what I really have is for the wires which I will filter.

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Right. I have the metal down I can do support and that they can heat it up and I have to figure out what's going on from that information. Now this is a typical situation. So we break the junction. This point a conductance here is a bog three point five conductance quanta which corresponds to two by.

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To kill all it's OK when you break that break in the junction and we utilize various sensitive very very very high resolution. P S which through this process. You see that we conduct doesn't change the allegation range of a fraction of and then suddenly jumps to some other point right.

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Then again there is sort of a slanted tall return to the generator. Then the jumps again and then when we inverse instead of breaking we start connecting the wire it comes back. The conductor is gross. Then the jumps back to some other where again there is a plateau and then jumps back to the same point where we're starting now just to tell you the whole braking process the whole cycle here is thirteen hours.

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It's thirteen hours where you're not exactly to the same conduct. By the total value of the conductor. We actually figure out that we came to the same point in terms of the differential conductance. And here is another story another short introduction to theoretical physics is required because what I marry here is the conventional self the niobium conflict in the superconducting state.

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Now some people can tell you wait. Or does it in their superconductivity means that the resistance has to go to zero in that's right. What he was talking about thirteen kilo means you know a ton of conduct. Is he lying. Now answer is NO I'M NOT LYING superconductivity and small sized not grouped together very well.

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So when you talk about someone taking about superconductivity at the nano scale take this into account. This is this is my explanation I've been in the field for many years. Superconductivity is formation of Cooper pairs. I can spare right. So the political will charge equal to two electrons.

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Without the UP THERE IS NO superconductivity How do they pair they pair through interactive but interaction through atomic letters and this is a very very simplistic explanation let's just assume that we have two electrons right in each atom gives one electron to the to the to recombine band right.

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And therefore we have positive ions Now imagine wrong the right the moves right. So what happens over the charges are slightly attractive. Right. So we have some some kind of perturbation all of those if you fire ants which track the direction of the motion of this will act now when the negative value like on that slice let's say in the opposite direction moves there.

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It's feels that extra charge which is left the slowed to relax the some massive particles but they're like times move fast. OK. This is a very simplistic explanation of course each elect them pairs not only with one run of lifetime but actually with it with several But let's not even go on.

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Go towards that. So this is the scene where that you have to remove that when you when you use got superconductivity this is an electron interacting with another one a through one. All right. Therefore this light tells you that you need for loans right you need the finite sized object for this particular interaction being possible.

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So when we have a number why are there are elements there from your peers there put the number wire as a matter of fact remains normal. Right. And this is standard between superconducting the electrodes we are the spare in the sports. OK So we have essentially what's called a superconductor a normal superconductor current that we're never would talk about even the metallic not even on the right made of the said metal between Baalke electrons.

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Now here's the question. Well superconductivity because of the so-called gap in the in the in the density of states. This means the following that. Believe at the from the energy all the electrons leave at the energy which is has its maximum managed by the value of the superconducting gap.

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Right. And can only be excited into the states which are two times the superconducting gap from from this highest occupies the all right so what happens. We have a superconducting normal superconductor contact with electrons in here. Can be moved to another superconductor if the energy is more than the energy of the Start by state and the answer is yes they can.

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There is a mechanism. And this is the mechanism which is responsible for that was when you ready to switch I showed you. Right. This is the reflection. So we need to be quick because time moves fast. I should just tell you that the mechanism in the superconductor interface.

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Being reflected and third pair in the superconductor and this group are part of them can be can be can be moved in the superconductor without any supervision. Now if the whole approach is this normal superconductor interface connection from here we reflect that there isn't a right. OK And this process can actually grow indefinitely.

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Surprisingly enough if there is no scattering No this process goes in definitely transfer from left to right. I you can ask me if there is a car and they answer if there is in the car and because with the probability there is in the I can move into the lap.

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So there is always a transport across the interface but the transport to the right is equal to the transfer to the left. So the net current there is zero. We have to do you have to shift the balance somehow by will to try and right then the right half and that current in the conduct.

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All right. The reflection as a matter of fact is very very peculiar So this is the energy of space. This is the real space ran an electron is reflected there's a hole and the parents forming the whole actually moves backwards along the same trajectory as they like. So this is the read through deflection this is not the specular reflection like you would have from a beam of light or just a particle hitting the hard surface.

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Right. So this means the failure. That's now assumed that we did break the balance and applied to rent that you cross this interface so an electron when it moves in the sandwich will now again and then when it reflects and becomes a whole the whole would be moving opposite to the voltage but it also has an opposite sign.

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Therefore it would keep accelerating in the same voltage. Therefore this is what is called multiple only if your flexion is likely mean you accelerate or if there is no scattering by just applying the constant voltage you can keep increasing the energy of the selected whole system until it is enough to actually get into the I'm not your byte state and then me right in the swept away.

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OK. Let me very quickly show this process this is this is this is what happens right. Assume that the world which is large enough so that we are and can be just accelerated and then drop in the other superconductor All right so we want these two results resulting in chum's of current characteristic from just below that this process is not possible.

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Bob that this is possible it generates a current therefore you will have a current step at the branch which is equal to times the Delta you remember you have to take of you to get Indian manager two times or superconducting to put this process. Now we are discussing the process with scattering the rustic you know rustic scattering right so what happens in this case.

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So in the law can be can go through. Or it can be reflected backwards. Right. It will be able to reach the other superconductor with a certain transmission probability the position of this step is not going to change its magnitude is going to go down. OK So now let's go even to a more complicated situation where you have this multiple Ondrea for flexions that is remember the electron is reflected as a whole the whole keeps accelerating keeps going in the energy it can be reflected as in the act and again by a pattern from a superconductor this process will result in the step at the British equal to two times the get divided by A and the brand is the just reflection.

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If you expect and the current characteristic is this so basically you I do not step wise processes all of them have well defined advantages which are related to superconducting gap and that's the material which is involved. And this actually cover this kind of gutter contains enough information to extract both the number and transmission coefficients of channels from superconducting transport.

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So there is a work of where there were three different methods that actually provided model car food or transport and the rack going through a channel with an arbitrary that is commission. So whenever you measure a current characteristic you have this step structure and what you are trying to do you are trying to basically just select the smallest.

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A number of channels for different shows that fit your experimental well. So without some some smarts to find a feed for a five channel conductor this is the smallest number of channels that describe Nairobi don't you take a broad five hour or so on the on the on the more than P.C. So this is not a simple simulation but ultimately pays off.

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So you do get these so called conductance channel composition. You can extract that they experimentally. OK And this is very important. So let's come back to the it is not business. So I showed you this curve. Now and tell you that we actually ended up at the same point where we started.

[00:40:48]
So this told us the following was told us that we are dealing with a very small atomic structure that just goes through several mechanical States. So we start with a few atoms then they become something else when they break but not good way because this is the problem in part with this because that has a very specific current characteristic.

[00:41:12]
But when we reconnect the conflict would go exactly back. So we can actually do the cycle many times. So we can work like this as well. So there's a very stable very small atomic structure then. We didn't do that but some people can do this kind of break in curves about ten thousand times and they can build this so-called conductance he's the Grahams So whenever they take a contact break it completely the content will go through a sequence of steps and we plug them into conductance used the ground.

[00:41:43]
So this gives you the most preferred autonomy configuration sort of speak when the wire breaks and this is the histogram for niobium in there you see that there is only one peak so there is a structure which is very very likely to occur. Whenever you have grow do such a process.

[00:42:02]
Reaches about here knowing that we actually took a much closer look at this region and discovered something very interesting. We discovered that actually there are two regions there between the conductor and so three in two conductors quanta that are separated by a narrow region which we call the artsy and or random Telegraph noice region.

[00:42:25]
So what happens is the following. When we and we do the many samples there were a different samples of the role thirty contacts realisation So we are sure that this is ubiquitous in this kind of cloud. OK this is what happens we see it here at Large come back not send keep stretching the right or we have a very specific differential conductor scar and we can say that when there were we have a contact like this there are at least two combatants channels with a very high transmission and what happens then when we see it here we have a very different differential conductance characteristic Roger peak of zero bias when pushed and there is no new branch channel with patient in this region which is always a bad point to Ron in charms if they are engaged.

[00:43:15]
What we observe here is the average conductors. But in fact if you do if you just record conduct of the function of time you see that combatants they prefer to eat between two levels. Which is just equal to this the conductance and this value of the conductors by stretching the contact you can actually adjust repopulation time in each of the states.

[00:43:40]
If the contact is compressed the system prefers sitting here. And if it contacts a strangely system prefers spending more time near the end this can observe superconducting States and again we started thinking that we have some atomic system which have two stable states between those come right. How do we figure out what the system is without.

[00:44:08]
Without looking into that this is where theorists with supercomputers very handy. And especially those that have that can combine two central methods for the more microscopic objects. One is the so-called. Density functional theory. It's the bell prize rather than the recall and I think right is a chemist and one is the function technique.

[00:44:35]
So do you. T. is the method for calculating the structure. So basically what you do is the problem. So you create a computer model and you take some atoms you throw them together and then you let them go. And then that would mean they want to go with me my is the energy of the system.

[00:44:57]
So the atoms in the computer self assemble into an equilibrium structure. OK this is D.F.T. this is how the structure is calculated function there is the typical calculation electron transport. So what this does is the following remember my discussion of the run dollar families and we have a plane wave then it goes through a channel or somebody object gets reflected and transmitted with a certain probability right.

[00:45:25]
This is at seven in logical theory. It doesn't take into account. A real structural for an object near magnetic luminance function to commute that apparently it is possible to calculate a real electron states. Of samey infinite objects like Harry would it leads right here or left and right.

[00:45:46]
And there is also possible to calculate and this means that you just have a not powerful enough computer the electronic state in the small object like here is what's called the device which is not a case in the rustics scatter. And then you can stand the real waves.

[00:46:03]
In the same elite into the real abject and relate and this is again this is the same in this same transmission picture as a matter of fact just have to be done. So this Green function technique allows you to relate those we functioned without actually going there was a way of equations which I sure didn't your equations in this case they do real quantum mechanical simulations and this is the net result the number and the transmission Confucians individual conductance channels are nature all products are first.

[00:46:36]
So if you look at the transporter Gratian read them. Through the I'm only going to countries. You can method you see that in it's exactly the same as the RAM dollar method. Right. And remember. So this now is the metrics that contains And remember we can determine that from measure.

[00:46:54]
OK And this has been put for the theorists. So basically here you have to be smart enough to guess what is in the contract. But they did few things they started with the configuration when this atom is shared between two leave it. Calculation showed that there is a very high conductor six conductors Kuantan that they didn't observe there is no possibility for the two mechanical States.

[00:47:20]
Then they had run at them suspended between the two keeps we come back and swim to learn more about quanta But again we didn't find. Mechanical States. Only when there was a dime or form in the computer Di Maria is a niobium to molecule. Right on the shoulder.

[00:47:37]
This is because this is it right the distance between the out themself to angstroms in the front two states the mechanical state as well as the combatants of the magnitude which made those of the experiment. OK So this is the picture over here of the state. This is when we see it at Sprott taught in.

[00:48:03]
He win by a dime or suspended be community superconducting tips right in the middle will conduct and state is when the shift towards one of the deep by a small amount of were happening. OK this is the result of the calculation. We're just shown here on molecular orbitals molecular bits else's work a lot of times a ride when we go and run conductor into another in this case there would be pictures are shown for the highs don't keep right on the Middle East on the right molecular orbitals right.

[00:48:33]
So this is what happened. We have been able to determine the structure of the rider over a smell a technical object by combining first principles simulations and transport measurements superconductivity was essentially here to give us the comparison of the transmission and I think in that question. All right so this was a publication in January two thousand and seven will do the work I took about two years to make systematic measurements because samples some not very easy to produce experiments have to be performed methodically.

[00:49:07]
Slide then a living thing was observed. So. We discussed already multiplicative reflection of the New Year mechanism which is called the multiplicity of perfections. Now we're going to really do in this experiment is that whenever we where in this state which was either of this. I do this hike and back and so when conducting a state.

[00:49:37]
This means there was a now remember that the structure is. We're always had additional peaks in the differential conductance cards speaks with the large. But definitely those peaks when that explained by the multiple reflections the theory of multiple may have actually done that explains all right so after you literature I found that the question of the interaction of bring with electronic transport is a very popular topic in.

[00:50:02]
Be filled with more like you want. Alec Tronics OK and he difference is that in the case of molecular trying to work with small objects molecules also even going to get it back. They work with electron transport and they case what happens is the following whether you break junction technique were a nest team technique you deposited the recommender more into them or killed.

[00:50:26]
It may or may not pick sides of the vibrational modes and then gets off the molecule. Actually both cases up passible one case is possible when in the right turn will generate the babe ration and we come back and severely depressed right so I can do this case we're actually in the hands they can back.

[00:50:46]
It's called from unhandsome tunnel and sometimes. All right. But there are also the making is in play that you have to take into account you have to take into account the capacitance so if there was some remember. So it would be a short is that my assessment of the Tronics is that we have still a long way to go.

[00:51:06]
And vibrations actually played Big Important that. OK so now I started thinking that maybe if we have in our case something similar. Right. We do have extra peaks which may be due to the interaction of electrons to compare pairs with this dimer that IMO is a molecule which is suspended between superconductors.

[00:51:28]
And maybe we do have some kind of interaction. So I'll run thing which I want to say up front is that there is a show not to be the interaction with the electricity but if the group there appears to prove that I have to go very quickly through a superconductivity primer and just tell you that so far you've been there were discussed the weakening between two superconductors we discussed only D.C. current right I was measuring by and by D.C. current and measuring D.C. car but you see that you're measuring D.C. current.

[00:51:59]
But in fact there's also may seek. That exists inside junction. So this is a discovery due to Brian joy of some. Nine hundred sixty two which when the bell provides very quickly after the discovery and basically let me tell you that without going through the questions that the jewel of some drunk show half of superconducting normal superconducting junction behaves as a weird touch controlled or so later on top of the D.C. current You also have been high frequency AC component.

[00:52:33]
Right. This is the this is what. Which is what happens the frequency is proportional to the way through this. Which is about five hundred megahertz really rolled into terahertz or build whatever you like more this is a very high frequency but it is very important is that this proportionality contains only fundamental constants and doesn't contain the shape of the junction.

[00:52:59]
It doesn't contain the really nature of a superconductor which is a sign of a great technology or write something that. You can make your vantage buyers and you get something which is frequency which is also a great thing to measure with a very high precision. OK. So for instance the applications like screeds superconducting quantum and the fear is devices and this is one of the most spectacular in my room to fuel application of those this is the answer for a longer.

[00:53:32]
This is where. Electric currents in the brain can be studied in response to students to why to park in the wrong with the early experiments and one thousand and one to run in the health and community of technology one of the conditions was to take a sound and drink five beers and then the story and measure the difference and where in the propagation in the last year.

[00:53:56]
Propagation of rhetoric or chorus of the brain and all and they have to make the. This is a new technique you don't know what to expect. OK but now it became actually one of the one of the very powerful medical techniques in a very short amount of time.

[00:54:15]
But what we want to actually discuss here is a little bit different story. So let me tell you very briefly about since you have an intrinsic effect right. You have this some current you can have frequency mix in fact one of the most famous is the so-called Shapiro steps is when you're eighty eight.

[00:54:39]
Of some Junction which is biased at the certain frequency with the radiation of the frequency that it matches the frequency of the current you have. Step and handsome and in the in the carnival which characteristics. This is actually the first experimental confirmation of the jewels of the thing by guy over and it was also in the belt prize.

[00:55:01]
OK so there is another effect which is due to the geometry of the jaws of some junction. But we basically for one. In the case of a dime are this is what happens. So if you look at the characteristic differential conductors clarity were detailed structure is from the peaks I was talking about.

[00:55:29]
OK. They said they did not call them the over the gap structure. You see that they disappear when you heat up the conflict above the superconducting the transition temperature they are not there. They're not there. Right. They seed they exist only in the superconductor state. OK I can explain actually why the script is normally or it has nothing to do at that high temperature so it has nothing to do with superconductivity there are some other processes involved but the other experiment that we needed Lee speaks shoot with the temperature.

[00:56:02]
If you have to. Something which is not joyous in the theatre later and I remember something doesn't have the gap. So it simply has a very rich versus frequency into fundamental concepts you would not expect this speaks to ship and this is what happens. Indeed we observe a series of peaks in the high conductance alone conduct state would use appear as the temperature goes up but they don't ship.

[00:56:24]
Therefore we associated them with the AC Josephs in effect. OK Now how do you confirm that this is what what happens. Well again theorists who supercomputers a handy and they take this structure and they calculate vibration models this is also a quantum calculation if you want to know the details of what we can talk later.

[00:56:44]
But basically they identified several modes the lowest frequency modes the chance for so long to do in the Reagan and they give me the mechanical frequency and it turns out that if you plot the frequency of those moments where it is the position of the Speaks. It's a perfect match.

[00:57:00]
We have the longer term build the radio. Mode and their second her morning against those peaks again first principle calculation compare with experiment. Read about the transfers moan moan corresponds to the voltage of bad run media well it's deep in the subject structure again substructure is very gigantic but if you're careful enough you can actually distinguish the speaker as well.

[00:57:25]
In accord. So from our point of view what would prove this before. One is that we can both the tactic side and detect the interaction of very high frequency intrinsic superconducting If that with atomic scale mechanical motion. So we can excite molecular vibrations. That's our our point of view right now.

[00:57:49]
Moreover if you look at this frequency this this frequencies are in a very desirable range right so the question is if I apply a run. Can I get five hundred. That hurts or not the answer is unfortunately OK but I can with niobium go as high as ten terahertz what happens a tenth or here it simply is the fall and when you frequency becomes too high you start exciting thermal problems ball in the niobium which transports superconductivity but I can sweep the voltage and I can get you and restoration everywhere between zero and OK So the question is if it were and of course when we start looking at that we got excited because there heard some making a comeback.

[00:58:40]
There is bass and there are several reasons for them. The reason is that there are security applications and image and applications which are based in part only on the fact that six point five terahertz is the nature of frequency all black body radiation from just us. OK And this is the demonstration by a company we should utilize a different methods that the consumer that can be found by basically emergent this happen.

[00:59:09]
This hidden under under under a piece of this or that can be distinguishable in principle we can package our jobs and junction in the image and cheap projection has to be a little bit different but we are thinking about that and the second one is of course the application to one single molecule spectroscopy.

[00:59:28]
So here is the idea is that if we can convince a man like you to get into the scene. With that or her source you to me may not excite the mechanical moments which will allow actually figure now the structure of the smaller kill from the vibrational spectrum.

[00:59:52]
I understand that this is a very important problem for instance in which army and promoting and structures the frequency of for some of those moments actually. In the range in the terahertz range and I think in about several different geometry it's hard to realize such as you write just as well as how to track them or look you'll into such a device.

[01:00:16]
All right so the time is up and I want to thank you once more and one more time. This is actually the same slide as before I now just don't put aside the fact that we discovered it was a dime or and this thread contains everything I told you about right.

[01:00:32]
Transport humiliations basic jewels and the fact and hopefully we can make it into that you can or would you with a help with this century on the words being built across the street. Thank you very much. Yes often very same time. Yes there were the where there were dancers yes there were Thames down.

[01:01:14]
Dorchen bought the word Thames down to manufacture those things on the piazza on the bottom water and then the Create the shoot in motion. So actually were there were people who were capable of having their skin in Tallinn microscope sort of thing right. So when you do have this kind of motion and this kind of motion we can actually make it and then we show that to the contact area.

[01:01:40]
It wouldn't be too much information except just to confirm that it's in the McConnell sharp structure as well. I'm across the street. So if you want to talk more. You know you're welcome. Again we at this point we're hoping to make the move more through the technological side and let's see what happens.