Discovery of orbital angular momentum monopoles boosts the emerging field of orbitronics, an energy-efficient alternative to electronics.
Orbital angular momentum monopoles have been the subject of great theoretical interest as they offer major practical advantages for the emerging field of orbitronics, a potential energy-efficient alternative to traditional electronics. Now, their existence has been demonstrated through a combination of robust theory and experiments at the Swiss Light Source SLS at Paul Scherrer Institute PSI.
From Electronics to Orbitronics
In contrast to electronics, which depend on the charge of electrons for data transfer, the next wave of eco-friendly technologies could use alternate electron properties to process information. Until recently, the main contender for a different type of ‘tronics’ has been spintronics. Here, the spin of the electron is the property used to transfer information.
Researchers are also exploring the possibility of using the orbital angular momentum (OAM) of electrons orbiting their atomic nucleus: an emerging field known as orbitronics. This field holds great promise for memory devices, particularly because a large magnetization could potentially be generated with relatively small charge currents, leading to energy-efficient devices. The million-dollar question now is identifying the right materials to generate flows of OAMs, a prerequisite for orbitronics.
Chiral Topological Semi-Metals: A Natural Fit for Orbitronics
Now an international research team led by scientists from Paul Scherrer Institute PSI and Max Planck Institutes in Halle and Dresden in Germany have shown that chiral topological semi-metals, a new class of materials discovered at PSI in 2019, possess properties that make them a highly practical choice for generating currents of OAMs. The discovery was published today (September 27) in the journal Nature Physics.
In the search for suitable materials for orbitronics, steps forward have already been made using conventional materials such as titanium. Yet since their discovery five years ago, chiral topological semi-metals have become an intriguing contender. These materials possess a helical atomic structure, which gives a natural ‘handedness’ like the DNA double helix and could naturally endow them with patterns or textures of OAM that enable its flow.
Unveiling the Potential of OAM Monopoles
“This offers a significant advantage to other materials because you don’t need to apply external stimuli to get OAM textures – they’re an intrinsic property of the material,” explains Michael Schüler, group leader in the Center for Scientific Computing, Theory and Data at PSI, and assistant professor of physics at the University of Fribourg, who co-led the recent study. “This could make it easier to create stable and efficient currents of OAM without needing special conditions.”
Challenges and Advances in OAM Monopole Detection
There is one particular OAM texture, hypothesized in chiral topological semi-metals, that has captivated researchers: OAM monopoles. At these monopoles, OAM radiates outwards from a center point like the spikes of a scared hedgehog curled into a ball.
Why these monopoles are so tantalizing is that OAM is uniform in all directions: i.e. it is isotropic. “This is a very useful property as it means flows of OAMs could be generated in any direction,” says Schüler.
Yet despite the attraction of OAM monopoles for orbitronics, until this latest study, they have remained a theoretical dream.
Hedgehogs Hide Between Theory and Experiment
To observe them experimentally, hope has lain with a technique known as Circular Dichroism in Angle-Resolved Photoemission Spectroscopy, or CD-ARPES, using circularly polarised X-rays from a synchrotron light source. Yet a gap between theory and experiment has in the past hindered researchers from interpreting the data. “Researchers may have had the data, but the evidence for OAM monopoles was buried in it,” says Schüler.
In ARPES, light shines on a material, ejecting electrons. The angles and energies of these ejected electrons reveal information on the electronic structure of the material. In CD-ARPES, the incident light is circularly polarised.
“A natural assumption is that if you use circularly polarised light, you are measuring something that is directly proportional to the OAMs,” explains Schüler. “The problem is, as we show in our study, this turns out to be a somewhat naïve assumption. In reality, it’s rather more complex.”
New Insights Into OAM Detection Techniques
In their study, Schüler and colleagues examined two types of chiral topological semi-metals at the Swiss Light Source SLS: those made of palladium and gallium or platinum and gallium. Determined to reveal the OAM textures hidden within the complex web of CD-ARPES data, the team challenged every assumption with rigorous theory.
Then they made an unusual, and crucial, extra experimental step of varying the photon energies. “At first, the data didn’t make sense. The signal seemed to be changing all over the place,” says Schüler.
Meticulously unpicking how different contributions complicated calculations of OAM from CD-ARPES data, they revealed that the CD-ARPES signal was not directly proportional to the OAMs, as previously believed, but rotated around the monopoles as the photon energy was changed. In this way, they bridged the gap between theory and experiment and proved the presence of OAM monopoles.
Future Directions in Orbitronics Research
Armed with the ability to accurately visualize OAM monopoles, Schüler and colleagues went on to show that the polarity of the monopole – whether the spikes of OAMs point inwards or outwards – could be reversed by using a crystal with a mirror image chirality. “This is a very useful property, as orbitronics devices could potentially be created with different directionality,” says Schüler.
Now, with theory and experiment finally united, the wider research community is equipped with the means to explore OAM textures across a variety of materials and optimize their applications for orbitronics.
Reference: “Controllable orbital angular momentum monopoles in chiral topological semimetals” by Yun Yen, Jonas A. Krieger, Mengyu Yao, Iñigo Robredo, Kaustuv Manna, Qun Yang, Emily C. McFarlane, Chandra Shekhar, Horst Borrmann, Samuel Stolz, Roland Widmer, Oliver Gröning, Vladimir N. Strocov, Stuart S. P. Parkin, Claudia Felser, Maia G. Vergniory, Michael Schüler and Niels B. M. Schröter, 30 September 2024, Nature Physics.
DOI: 10.1038/s41567-024-02655-1
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1 Comment
Memo 2409280537
It seems that my existing conceptual modeling can show the true nature of the emerging quantum twist and the emerging orbitronics as the energy-efficient technology of the future. Huh.
The problem is, as always shown in the memorization, this is a rather naive assumption. In reality, it is much more complicated.
Source1.Edit
1. Monopoles of orbital angular momentum (OAM) are enticing prospects for orbital electronics, as OAMs are uniform in all directions. This means that information flows can be generated in either direction.
-It is reminiscent of modeling the side value of qpeoms as the diameter of a sphere.
2. The team showed that chiral topological semimetals, a new kind of material discovered in PSI in 2019, have properties that make them a very practical choice in generating OAM currents.
In the process of finding materials suitable for orbitronics, conventional materials such as titanium have already taken it to the next level. However, since its discovery five years ago, chiral topological semimetals have become an interesting competitor. These materials have a helical atomic structure, providing a natural ‘handiness’ like a DNA double helix, and can naturally give patterns or textures of OAMs, enabling flow.
-Chiral topology semimetallic obitronics is reminiscent of the meta structure of my oms.vix.ain. Semi-metallic and antimaterial. Has chiral line symmetry structure and completes omsfull on topological ulcers. Uh huh.
3.OAM Monopole’s Potential Revealed
“This provides a significant advantage for other materials as it is not necessary to apply external stimuli to obtain the OAM texture. It is an essential property of the material. This can make it easier to create stable and efficient OAM currents without any special conditions.
-The chiral structure twist oms.vix.ain makes itself inside without external stimulation and presents the same color full value to the outside like a cubby puzzle. But is it one color? It was only two black and white. Uh-huh. Of course, six typical cubic puzzles appear.
4. Challenges and Advances in OAM Monopole Detection
There is one particular OAM texture assumed to be the chiral phase semimetal that has captivated the researchers. It is an OAM unipolar body. In this unipolar body, OAM is radiated outward from the center point, like the thorn of a scared hedgehog rolled into a ball.
The reason why these monopoles are so attractive is that OAMs are uniform in all directions. That is, isotropy. This is a very useful attribute, which means that OAM flows can be generated in either direction.
-The values of the angles and diagonals of qpeoms are the same in all ?xyzz’ directions, like the thorn of a hedgehog. If placed on the surface of the sphere, it is the diameter of the full sphere directed toward the body like the thorn of the hedgehog.
5.In ARPES, light emits electrons in light of a material. The angles and energies of the emitted electrons show information about the electronic structure of the material. In CD-ARPES, the incident light is circularly polarized.
The natural assumption is that the use of circularly polarized light measures what is directly proportional to the OAM. The problem is, as our study shows, this is a rather naive assumption. In reality, it is much more complex.
They carried out an unusual and important additional experimental step to change the photon energy. It was revealed that the photon energy rotates around the unipole as it changes. In this way they bridged the gap between theory and experiment and proved the existence of an OAM unipole.
6. Future Direction of Orbitronics Research
Armed with the ability to accurately visualize OAM monopoles, Schüler and colleagues showed that the polarity of monopoles (whether the spike of OAM points inward or outward) can be inverted using crystals with mirror chirality. This is a very useful property, as orbital electronics could potentially have different orientations.
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Source 1
https://scitechdaily.com/quantum-twist-orbitronics-emerges-as-energy-efficient-tech-of-tomorrow/
Quantum Twist: Orbitronics Emerges As Energy-Efficient Technology Of The Future