Spin Currents for Advanced Electronic Devices

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Spin Currents for Advanced Electronic Devices

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Spin Currents for Advanced Electronic Devices
Graphene-based van der Waals heterostructures could be used to design ultra-compact and low-energy electronic devices and magnetic memory devices, according to a study led by ICREA Prof. Sergio O. Valenzuela, head of the ICN2 Physics and Engineering of Nanodevices Group. [15]
A new method that precisely measures the mysterious behavior and magnetic properties of electrons flowing across the surface of quantum materials could open a path to nextgeneration electronics. [14]
The emerging field of spintronics aims to exploit the spin of the electron. [13]
In a new study, researchers measure the spin properties of electronic states produced in singlet fission – a process which could have a central role in the future development of solar cells. [12]
In some chemical reactions both electrons and protons move together. When they transfer, they can move concertedly or in separate steps. Light-induced reactions of this sort are particularly relevant to biological systems, such as Photosystem II where plants use photons from the sun to convert water into oxygen. [11]
EPFL researchers have found that water molecules are 10,000 times more sensitive to ions than previously thought. [10]
Working with colleagues at the Harvard-MIT Center for Ultracold Atoms, a group led by Harvard Professor of Physics Mikhail Lukin and MIT Professor of Physics Vladan Vuletic have managed to coax photons into binding together to form molecules – a state of matter that, until recently, had been purely theoretical. The work is described in a September 25 paper in Nature.
New ideas for interactions and particles: This paper examines the possibility to origin the Spontaneously Broken Symmetries from the Planck Distribution Law. This way we get a Unification of the Strong, Electromagnetic, and Weak Interactions from the interference occurrences of oscillators. Understanding that the relativistic mass change is the result of the magnetic induction we arrive to the conclusion that the Gravitational Force is also based on the electromagnetic forces, getting a Unified Relativistic Quantum Theory of all 4 Interactions.
Generation and manipulation of spin currents for advanced electronic devices ................................ 3
Spin current detection in quantum materials unlocks potential for alternative electronics................. 4
Device design allows ten-fold increase in spin currents ..................................................................... 5
Researchers road-test powerful method for studying singlet fission .................................................. 5

Using light to move electrons and protons.......................................................................................... 7 A single ion impacts a million water molecules................................................................................... 8
Not 100 but 1,000,000 molecules react .......................................................................................... 8 The molecules line up around the ions ........................................................................................... 8 From atomistic to macroscopic length scales ................................................................................. 9 Testing different salts and different "waters"................................................................................... 9 No link with water memory .............................................................................................................. 9 Photonic molecules ............................................................................................................................. 9 The Electromagnetic Interaction ....................................................................................................... 10 Asymmetry in the interference occurrences of oscillators ................................................................ 10 Spontaneously broken symmetry in the Planck distribution law....................................................... 11 The structure of the proton................................................................................................................ 13 The Strong Interaction....................................................................................................................... 14 Confinement and Asymptotic Freedom......................................................................................... 14 The weak interaction ......................................................................................................................... 14 The General Weak Interaction .......................................................................................................... 15 Fermions and Bosons ....................................................................................................................... 16 The fermions' spin ............................................................................................................................. 16 The source of the Maxwell equations ............................................................................................... 17 The Special Relativity........................................................................................................................ 18 The Heisenberg Uncertainty Principle .............................................................................................. 18 The Gravitational force...................................................................................................................... 18 The Graviton...................................................................................................................................... 19 What is the Spin? .............................................................................................................................. 19 The Casimir effect ............................................................................................................................. 19 The Fine structure constant .............................................................................................................. 20 Path integral formulation of Quantum Mechanics............................................................................. 21 Conclusions....................................................................................................................................... 21

References ........................................................................................................................................ 21
Author: George Rajna
Generation and manipulation of spin currents for advanced electronic devices
Graphene-based van der Waals heterostructures could be used to design ultra-compact and low-energy electronic devices and magnetic memory devices, according to a study led by ICREA Prof. Sergio O. Valenzuela, head of the ICN2 Physics and Engineering of Nanodevices Group. This is what a paper published in the latest issue of the journal suggests. The results have shown that it is possible to perform an efficient and tunable spin-charge conversion in these structures, and, for the first time, even at room temperature. The paper is published in Nature Materials. The first authors are L. Antonio Benítez and Williams Savero Torres, of the same group. The results complement recent studies carried out within this same initiative, including one published in 2019 in Nano Letters by scientists from the University of Groningen (RUG).
Spintronics, electronics that use electron spin to store, manipulate and transfer information,
comprises key technologies, such as those of motion sensors and information storage technologies. However, the development of efficient and versatile spin-based technologies requires high-quality materials
that allow long-distance spin transfer, as well as methods to generate and manipulate spin currents.
Spin currents are usually produced and detected using ferromagnetic materials. As an alternative, spin-orbit interactions allow the generation and control of spin currents exclusively through electric fields, providing a much more versatile tool for the implementation of large-scale spin devices.
Graphene is a unique material for long-distance spin transport. The new study demonstrates that spin transport can be manipulated in graphene by proximity effects. To induce these effects, the researchers
used transition metal dichalcogenides, which are two-dimensional materials like
graphene. The team has demonstrated efficient spin-charge interconversion at room temperature comparable to the best performance of traditional materials.
These advances are the result of a joint effort by experimental and theoretical researchers, who worked side by side in the framework of the Graphene Flagship. The outcomes of this study are of great relevance
for the communities of spintronics and two-dimensional materials, as they provide relevant information on the fundamental physics of the phenomena involved and open the door to new
applications. [15]

Spin current detection in quantum materials unlocks potential for alternative electronics
A new method that precisely measures the mysterious behavior and magnetic properties of electrons flowing across the surface of quantum materials could open a path to next-generation electronics.
Found at the heart of electronic devices, silicon-based semiconductors rely on the controlled electrical current responsible for powering electronics. These semiconductors can only access the electrons' charge for energy, but electrons do more than carry a charge. They also have intrinsic angular momentum known as spin, which is a feature of quantum materials that, while elusive, can be manipulated to enhance electronic devices.
A team of scientists, led by An-Ping Li at the Department of Energy's Oak Ridge National Laboratory, has developed an innovative microscopy technique to detect the spin of electrons in topological insulators, a new kind of quantum material that could be used in applications such as spintronics and quantum computing.
"The spin current, namely the total angular momentum of moving electrons, is a behavior in topological insulators that could not be accounted for until a spin-sensitive method was developed," Li said.
Electronic devices continue to evolve rapidly and require more power packed into smaller components. This prompts the need for less costly, energy-efficient alternatives to charge-based electronics. A topological insulator carries electrical current along its surface, while deeper within the bulk material, it acts as an insulator. Electrons flowing across the material's surface exhibit uniform spin directions, unlike in a semiconductor where electrons spin in varying directions.
"Charge-based devices are less energy efficient than spin-based ones," said Li. "For spins to be useful, we need to control both their flow and orientation."
To detect and better understand this quirky particle behavior, the team needed a method sensitive to the spin of moving electrons. Their new microscopy approach was tested on a single crystal of Bi2Te2Se, a material containing bismuth, tellurium and selenium. It measured how much voltage was produced along the material's surface as the flow of electrons moved between specific points while sensing the voltage for each electron's spin.
The new method builds on a four-probe scanning tunneling microscope—an instrument that can pinpoint a material's atomic activity with four movable probing tips—by adding a component to observe the spin behavior of electrons on the material's surface. This approach not only includes spin sensitivity measurements. It also confines the current to a small area on the surface, which helps to keep electrons from escaping beneath the surface, providing high-resolution results.
"We successfully detected a voltage generated by the electron's spin current," said Li, who coauthored a paper published by Physical Review Letters that explains the method. "This work provides clear evidence of the spin current in topological insulators and opens a new avenue to

study other quantum materials that could ultimately be applied in next-generation electronic devices." [14]
Device design allows ten-fold increase in spin currents
An electron carries electrical charge and spin that gives rise to a magnetic moment and can therefore interact with external magnetic fields. Conventional electronics are based on the charge of the electron. The emerging field of spintronics aims to exploit the spin of the electron. Using spins as elementary units in computing and highly efficient electronics is the ultimate goal of spintronic science because of spintronics minimal energy use. In this study, researchers manipulated and amplified the spin current through the design of the layered structures, a vital step towards this goal.
For cell phones, computers, and other electronic devices, a major shortcoming is the generation of heat when electrons move around the electronic circuits. The energy loss significantly reduces the device efficiency. Ultimately, the heat limits the packing of components in high-density microchips. Spintronics' promise is to eliminate this energy loss. It does so by just moving the electron spin without moving the electrons. Using design strategies such as those identified by this research could result in highly energy-efficient spintronics to replace today's electronics.
An important obstacle to realizing spintronics is the amplification of small spin signals. In conventional electronics, amplification of an electron current is achieved using transistors. Recently, researchers at Johns Hopkins University demonstrated that small spin currents can be amplified by inserting thin films of antiferromagnetic (materials in which the magnetic moments are canceled ) insulator materials into the layered structures, effectively producing a spintransistor. Scientists used thin films of antiferromagnetic insulators, such as nickel and cobalt oxide, sandwiched between ferrimagnetic insulator yttrium iron garnet (YIG) and normal metal films. With such devices, they showed that the pure spin current thermally injected from YIG into the metal can be amplified up to ten-fold by the antiferromagnetic insulator film. The researchers found that spin fluctuation of the antiferromagnetic insulating layer enhances the spin current. They also found that the amplification is linearly proportional to spin mixing conductance of the normal metal and the YIG. The experiments demonstrated this effect for various metals. Further, the study showed that the spin current amplification is proportional to the spin mixing conductance of YIG/metal systems for different metals. Calculations of the spin current enhancement and spin mixing conductance provided qualitative agreement with the experimental observations. [13]
Researchers road-test powerful method for studying singlet fission
In a new study, researchers measure the spin properties of electronic states produced in singlet fission – a process which could have a central role in the future development of solar cells.
Physicists have successfully employed a powerful technique for studying electrons generated through singlet fission, a process which it is believed will be key to more efficient solar energy production in years to come.

Their approach, reported in the journal Nature Physics, employed lasers, microwave radiation and magnetic fields to analyse the spin of excitons, which are energetically excited particles formed in molecular systems.
These are generated as a result of singlet fission, a process that researchers around the world are trying to understand fully in order to use it to better harness energy from the sun. Using materials exhibiting singlet fission in solar cells could make energy production much more efficient in the future, but the process needs to be fully understood in order to optimize the relevant materials and design appropriate technologies to exploit it.
In most existing solar cells, light particles (or photons) are absorbed by a semiconducting material, such as silicon. Each photon stimulates an electron in the material's atomic structure, giving a single electron enough energy to move. This can then potentially be extracted as electrical current.
In some materials, however, the absorption of a single photon initially creates one higher-energy, excited particle, called a spin singlet exciton. This singlet can also share its energy with another molecule, forming two lower-energy excitons, rather than just one. These lower-energy particles are called spin "triplet" excitons. Each triplet can move through the molecular structure of the material and be used to produce charge.
The splitting process - from one absorbed photon to two energetic triplet excitons - is singlet fission. For scientists studying how to generate more solar power, it represents a potential bargain - a twofor-one offer on the amount of electrical current generated, relative to the amount of light put in. If materials capable of singlet fission can be integrated into solar cells, it will become possible to generate energy more efficiently from sunlight.
But achieving this is far from straightforward. One challenge is that the pairs of triplet excitons only last for a tiny fraction of a second, and must be separated and used before they decay. Their lifespan is connected to their relative "spin", which is a unique property of elementary particles and is an intrinsic angular momentum.
Studying and measuring spin through time, from the initial formation of the pairs to their decay, is essential if they are to be harnessed.
In the new study, researchers from the University of Cambridge and the Freie Universität Berlin (FUB) utilised a method that allows the spin properties of materials to be measured through time. The approach, called electron spin resonance (ESR) spectroscopy, has been used and improved since its discovery over 50 years ago to better understand how spin impacts on many different natural phenomena.
It involves placing the material being studied within a large electromagnet, and then using laser light to excite molecules within the sample, and microwave radiation to measure how the spin changes over time. This is especially useful when studying triplet states formed by singlet fission as these are difficult to study using most other techniques.
Because the excitons' spin interacts with microwave radiation and magnetic fields, these interactions can be used as an additional way to understand what happens to the triplet pairs after

they are formed. In short, the approach allowed the researchers to effectively watch and manipulate the spin state of triplet pairs through time, following formation by singlet fission.
The study was led by Professor Jan Behrends at the Freie Universität Berlin (FUB), Dr Akshay Rao, a College Research Associate at St John's College, University of Cambridge, and Professor Neil Greenham in the Department of Physics, University of Cambridge.
Leah Weiss, a Gates-Cambridge Scholar and PhD student in Physics based at Trinity College, Cambridge, was the paper's first author. "This research has opened up many new questions," she said. "What makes these excited states either separate and become independent, or stay together as a pair, are questions that we need to answer before we can make use of them."
The researchers were able to look at the spin states of the triplet excitons in considerable detail. They observed pairs had formed which variously had both weakly and strongly-linked spin states, reflecting the co-existence of pairs that were spatially close and further apart. Intriguingly, the group found that some pairs which they would have expected to decay very quickly, due to their close proximity, actually survived for several microseconds.
"Finding those pairs in particular was completely unexpected," Weiss added. We think that they could be protected by their overall spin state, making it harder for them to decay. Continued research will focus on making devices and examining how these states can be harnessed for use in solar cells."
Professor Behrends added: "This interdisciplinary collaboration nicely demonstrates that bringing together expertise from different fields can provide novel and striking insights. Future studies will need to address how to efficiently split the strongly-coupled states that we observed here, to improve the yield from singlet fission cells."
Beyond trying to improve photovoltaic technologies, the research also has implications for wider efforts to create fast and efficient electronics using spin, so-called "spintronic" devices, which similarly rely on being able to measure and control the spin properties of electrons. [12]
Using light to move electrons and protons
In some chemical reactions both electrons and protons move together. When they transfer, they can move concertedly or in separate steps. Light-induced reactions of this sort are particularly relevant to biological systems, such as Photosystem II where plants use photons from the sun to convert water into oxygen.
To better understand how light can lead to the transfer of protons in a chemical reaction, a group of researchers from the University of North Carolina, Shanxi University in China, and Memorial University in Newfoundland have conducted adsorption studies on a new family of experiments to observe the transition that occurs when protons transfer between hydrogen-bonded complexes in solution . They provide evidence for new optical transitions characteristic of the direct transfer of a proton. This report recently appeared in the Proceedings of the National Academy of Sciences.
N-methyl-4,4'-bipyridinium cation (MQ+) serves as proton acceptor, where a proton will add to the non-methylated pyridinium amine. If proton transfer occurs, then MQ+ will form a radical cation

(MQH+•) whose absorbance spectra in the UV/visible range can be compared to N, N'-dimethyl-4, 4'-bypyridinium (MV2+).
By using ultrafast laser flash photolysis measurements, they found direct evidence for a low energy absorption band between p-methoxyphenyl and the mehylviologen acceptor, MQ+. It appears at 360 nm and as early as 250 fs after the laser pulse. Based on these properties, it is clearly the product of proton transfer from the phenol to give MeOPhO•—H-MQ+.
The appearance of this reaction involving the transfer of both an electron and proton after absorbing a single photon is supported by the vibrational coherence of the radical cation and by it characteristic spectral properties. By inference, related transitions, which are often at low intensities, could play an important role in the degradation of certain biological molecules, such as DNA.
The appearance of these absorption bands could have theoretical significance. They demonstrate a way to use simple spectroscopic measurements to explore the intimate details of how these reactions occur in nature. This provides new physical insight into processes that could be of broad biological and chemical relevance. [11]
A single ion impacts a million water molecules
EPFL researchers have found that water molecules are 10,000 times more sensitive to ions than previously thought.
Water is simple and complex at the same time. A single water molecule (H2O) is made up of only 3 atoms. Yet the collective behavior of water molecules is unique and continues to amaze us. Water molecules are linked together by hydrogen bonds that break and form several thousands of billions of times per second. These bonds provide water with unique and unusual properties. Living organisms contain around 60% water and salt. Deciphering the interactions among water, salt and ions is thus fundamentally important for understanding life.
Not 100 but 1,000,000 molecules react
Researchers at EPFL's Laboratory for fundamental BioPhotonics, led by Sylvie Roke, have probed the influence of ions on the structure of water with unprecedentedly sensitive measurements. According to their multi-scale analyses, a single ion has an influence on millions of water molecules, i.e. 10,000 times more than previously thought. In an article appearing in Science Advances, they explain how a single ion can "twist" the bonds of several million water molecules over a distance exceeding 20 nanometers causing the liquid to become "stiffer". "Until now it was not possible to see beyond a hundred molecules. Our measurements show that water is much more sensitive to ions than we thought," said Roke, who was also surprised by this result.
The molecules line up around the ions
Water molecules are made up of one negatively charged oxygen atom and two positively charged hydrogen atoms. The Mickey Mouse-shaped molecule therefore does not have the same charge at its center as at its extremities. When an ion, which is an electrically charged atom, comes into contact with water, the network of hydrogen bonds is perturbed. The perturbation spreads over

millions of surrounding molecules, causing water molecules to align preferentially in a specific direction. This can be thought of as water molecules "stiffening their network" between the various ions.
From atomistic to macroscopic length scales
Water's behavior was tested with three different approaches: ultrafast optical measurements, which revealed the arrangement of molecules on the nanometric scale; a computer simulation on the atomic scale; and measurement of the water's surface structure and tension, which was done at the macroscopic level. "For the last method, we simply dipped a thin metal plate into the water and pulled gently using a tensiometer to determine the water's resistance," said Roke. "We observed that the presence of a few ions makes it easier to pull the plate out, that is, ions reduce the surface resistance of water. This strange effect had already been observed in 1941, but it remained unexplained until now. Through our multiscale analysis we were able to link it to ioninduced stiffening of the bulk hydrogen bond network: a stiffer bulk results in a comparatively more flexible surface."
Testing different salts and different "waters"
The researchers carried out the same experiment with 21 different salts: they all affected water in the same way. Then they studied the effect of ions on heavy water, whose hydrogen atoms are heavy isotopes (with an additional neutron in the nucleus). This liquid is almost indistinguishable from normal water. But here the properties are very different. To perturb the heavy water in the same way, it required a concentration of ions six times higher. Further evidence of the uniqueness of water.
No link with water memory
Roke and her team are aware that it might be tempting to link these stunning results to all sorts of controversial beliefs about water. They are however careful to distance themselves from any farfetched interpretation. "Our research has nothing to do with water memory or homeopathy," she said. "We collect scientific data, which are all verifiable. "To prove the role of water in homeopathy, another million-billion-billion water molecules would have to be affected to even come close, and even then we are not certain."
The new discovery about the behavior of water will be useful in fundamental research, and in other areas too. The interaction between water and ions is omnipresent in biological processes related to enzymes, ion channels and protein folding. Every new piece of knowledge gives greater insight into how life works. [10]
Photonic molecules
Working with colleagues at the Harvard-MIT Center for Ultracold Atoms, a group led by Harvard Professor of Physics Mikhail Lukin and MIT Professor of Physics Vladan Vuletic have managed to coax photons into binding together to form molecules – a state of matter that, until recently, had been purely theoretical. The work is described in a September 25 paper in Nature.

The discovery, Lukin said, runs contrary to decades of accepted wisdom about the nature of light. Photons have long been described as massless particles which don't interact with each other – shine two laser beams at each other, he said, and they simply pass through one another.
"Photonic molecules," however, behave less like traditional lasers and more like something you might find in science fiction – the light saber.
"Most of the properties of light we know about originate from the fact that photons are massless, and that they do not interact with each other," Lukin said. "What we have done is create a special type of medium in which photons interact with each other so strongly that they begin to act as though they have mass, and they bind together to form molecules. This type of photonic bound state has been discussed theoretically for quite a while, but until now it hadn't been observed. [9]
The Electromagnetic Interaction
This paper explains the magnetic effect of the electric current from the observed effects of the accelerating electrons, causing naturally the experienced changes of the electric field potential along the electric wire. The accelerating electrons explain not only the Maxwell Equations and the Special Relativity, but the Heisenberg Uncertainty Relation, the wave particle duality and the electron’s spin also, building the bridge between the Classical and Quantum Theories. [2]
Asymmetry in the interference occurrences of oscillators
The asymmetrical configurations are stable objects of the real physical world, because they cannot annihilate. One of the most obvious asymmetry is the proton – electron mass rate Mp = 1840 Me while they have equal charge. We explain this fact by the strong interaction of the proton, but how remember it his strong interaction ability for example in the H – atom where are only electromagnetic interactions among proton and electron.
This gives us the idea to origin the mass of proton from the electromagnetic interactions by the way interference occurrences of oscillators. The uncertainty relation of Heisenberg makes sure that the particles are oscillating.
The resultant intensity due to n equally spaced oscillators, all of equal amplitude but different from one another in phase, either because they are driven differently in phase or because we are looking at them an angle such that there is a difference in time delay:
(1) I = I0 sin2 n φ/2 / sin2 φ/2
If φ is infinitesimal so that sinφ = φ than
(2) ι = n2 ι0
This gives us the idea of
(3) Mp = n2 Me
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