Superconducting spin-electronics
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| Anzahl der Teile | 163 | |
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| Lizenz | CC-Namensnennung - keine Bearbeitung 4.0 International: Sie dürfen das Werk in unveränderter Form zu jedem legalen Zweck nutzen, vervielfältigen, verbreiten und öffentlich zugänglich machen, sofern Sie den Namen des Autors/Rechteinhabers in der von ihm festgelegten Weise nennen. | |
| Identifikatoren | 10.5446/50323 (DOI) | |
| Herausgeber | 05jdrrw50 (ROR) | |
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Elektron <Legierung>GermaneProspektionChemische StrukturFunktionelle GruppeEnhancerComputeranimation
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Funktionelle GruppeEnhancerHybridisierung <Chemie>
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Elektron <Legierung>
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Klinische ChemieBukett <Wein>Chemisches Experiment
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AzokupplungElektron <Legierung>CHARGE-Assoziation
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KorngrenzeFleischerCHARGE-AssoziationElektron <Legierung>PhasengleichgewichtChemisches Experiment
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NiobHolmiumMagnetisierbarkeitHolmiumNiobAzokupplungReaktionsmechanismusMetallChemische EigenschaftNahtoderfahrungKorngrenzeOberflächenchemiePegel <Hydrologie>Bukett <Wein>ReglersubstanzKooperativitätElektronische Zigarette
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Systemische Therapie <Pharmakologie>CarbonatplattformHeliumVerdünnerChemisches Experiment
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Transkript: Englisch(automatisch erzeugt)
00:13
My name is Torsten Piech. In my group here at the University of Konstanz in southern Germany, we explore new exciting phenomena in hybrid nanostructures,
00:22
which one day will help us to make even smaller and faster devices. In this video, we will introduce the concept of superconducting spin electronics. At the moment, this is just a vision, but the foundations are already studied in our labs. Electronic wearables and the Internet of Things are designed to make our lives easier.
00:41
Nowadays, everybody owns a smartphone, but did you ever notice how hot they get? Today, electronic circuits are made of transistors and wires as small as 15 nm. At these dimensions, heat dissipation becomes a real issue, and the laws of classical physics are no longer applicable as we enter the strange world of quantum mechanics.
01:02
So clearly, a new technology is needed, one that doesn't have these issues, and spin-based electronics may just be the answer. In contrast to normal electronics, in spin electronics, not only the charge of the electron is used to decode information, but also its spin, a quantum mechanical property that gives the electron a tiny magnetic moment.
01:22
The spin is represented as an arrow that can be either up or down. Hence, there are two different types of electrons. Magnetism is a collective phenomenon involving many spins, and therefore, magnetic materials are the basic elements of spin electronic devices. But moving electrons in a wire still generates heat due to electrical resistance.
01:43
So why not combine magnetic materials with superconductors, which don't have any electrical resistance, to make superconducting spin electronics or short super-spin-tronics? Combining magnets and superconductors to useful devices is actually much more difficult than it sounds.
02:00
Ferromagnetism and superconductivity are often said to be competing or antagonistic effects, meaning they don't fit together well. For example, we don't know of any material that is both ferromagnetic and superconducting at the same time. This antagonism manifests itself in response of both materials to a magnetic field.
02:21
A ferromagnet concentrates the external field in its center, while a superconductor repels the magnetic field. The origin of this competition again lies within the spin. It leads to many interesting interface and proximity effects, which are studied in my group. My colleague Simon will now explain the microscopic origin of this competition.
02:42
And he will show that superconductivity and ferromagnetism can indeed coexist, despite their competing order parameters, but only when their interface is well designed. If we now want to build superconducting spintronic devices, we face a serious problem. The electrons responsible for carrying charge inside a superconductor always compound into pairs.
03:03
And those pairs almost always have opposing spin. This is a problem if we want cupopairs to carry spin information for us, because the total spin of a cupopair is always zero. And it's an even bigger problem if we want these cupopairs to penetrate a ferromagnetic device, because ideally, inside a ferromagnet, there's only one spin direction available,
03:24
the one the ferromagnet is magnetized in. Which means that traditionally, inside a ferromagnet, a cupopair should not be able to exist. My project now focuses on forcing electrons with the same spin to form cupopairs.
03:40
Those cupopairs would carry spin information, and they would be able to penetrate a ferromagnet, which is what we want for spintronics. Current research shows that the best way to achieve this is to take a normal cupopair and force it through a ferromagnetic interface that exposes it to two different non-cooled-in-neon magnetizations.
04:02
This way, the electrons in the cupopair are rotated and then flipped until a cupopair with equal spin is formed. Here, in Constance, we use ultra-high-resolution scanning probe techniques. This helps us to gain a better understanding on how exactly those cupopairs are formed.
04:21
In our most recent publication, we used cupopairs created in superconducting niobium and looked at their behavior after exposing them to a thin film of ferromagnetic holmium. The natural magnetic order in holmium provides us directly with a non-coolinium magnetization that forces these cupopairs to adapt an equal spin pairing.
04:42
By using a very sharp metal tip and positioning it only a couple of nanometers above the surface of the film, we can make electrons tunnel into the multilayer. And by analyzing their tunneling properties and by looking at their energy spectra, we can draw a conclusion about the exact creation mechanism happening at the ferromagnetic interface. An interface with non-coolinium magnetizations is not the only way how such cupopairs can be created.
05:05
My colleague Marcel will now show an alternative concept how such pairs can be created. The extraordinary element, holmium, is characterized by spatial inhomogenic magnetic properties.
05:20
This may be very useful and was used to explore properties of ferromagnetic superconducting systems. The question I'm trying to answer is, can we create cupopairs in ordinary collinear ferromagnet with a dynamic magnetization?
05:42
To investigate this, I analyze a small junction between superconductors with a ferromagnetic spacer. This spacer is driven in a ferromagnetic resonance. This means that the spins in this material are processing along the magnetization axis.
06:01
The basic idea is that we can transform the cupopairs from a superconductor with this procession into cupopairs in a ferromagnet and hence leads to a super current. The fundamental change of physical properties can be seen in transport spectroscopy.
06:21
In particular, the current voltage characteristics. Let's look at a normal conductor which is interrupted by a ferromagnet. In this case, we will see a linear dependence of voltage and current according to Ohm's law. However, if we exchange the normal conductor with a superconductor, the Ohm's law isn't valid anymore.
06:41
Now, if the interrupting spacer is small enough that cupopairs can tunnel through the barrier, one measures a current over the device without any voltage applied until a critical current is reached and then it jumps back to the normal conducting curve we saw before. With a ferromagnetic spacer, it is quite difficult to reach such circumstances due to the suppressed proximity effect.
07:07
The ferromagnet thickness would need to be only a few atoms. However, if the processing magnetization converts the cupopairs in a superconductor to cupopairs in the ferromagnet, then again a super current can be measured.
07:23
Even if the magnetic space is very thick and this is what I'm looking for. By applying an alternating current to such a junction, now this is where it gets complicated, we can see so-called Shapiro steps due to the AC Josephson effect.
07:43
These steps are replicas of the super current branch and can be used to analyze the superconducting current phase relationship of our junctions, which in essence is the fingerprint of a Josephson junction and tells you almost everything about its properties. Now, let's go to take a look how we measure.
08:02
Now we are in our low temperature lab. This one here is a dilution refrigerator, which I use for my measurements. This rod here is the insert and is going down into a liquid helium bath. It is the actual heart of a cryogenic system and it consists of the measuring wires of several filter stages
08:26
and the measuring platform and of course the dilution system. With this setup here, we are able to achieve temperature down to 40 millikelvin. The cooling power is provided by the heat of mixing of helium-4 and helium-3 isotopes.
08:48
This board here at the bottom is the sample holder on which we attach our chip. This chip is a silicon wafer and is structured by usual lithographical methods.
09:01
The final structure on it is about 100 nanometers and by the actual Josephson conduct. Our research clearly indicates that superconductor ferromagnet hybrid nanostructures can indeed support a dissipationless supercurrent. These devices show fundamentally new properties, which we are just beginning to understand.
09:25
So, there is a lot more to discover in the future before the vision of super-spintronics can be realized.