Quantum materials: electron spin measured for the first time

Quantum materials: electron spin measured for the first time

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Three perspectives of the surface on which the electrons move. On the left the experimental result, in the center and on the right the theoretical modeling. The red and blue colors represent a measure of the speed of the electrons. Both theory and experiment reflect the symmetry of the crystal, very similar to the texture of traditional Japanese “kagome” baskets. Credits: University of Bologna

An international research group has succeeded for the first time in measuring the spin of the electron in matter, i.e. the curvature of the space in which electrons live and move within “kagome materials”, a new class of quantum materials.

The obtained results published in Physics of natureit could revolutionize the way quantum materials are studied in the future, opening the door to new developments in quantum technologies, with possible applications in a variety of technological fields, from renewable energy to biomedicine, from electronics to quantum computers.

The success was achieved by an international collaboration of scientists, in which Domenico Di Sante, professor at the “Augusto Righi” Department of Physics and Astronomy, participated for the University of Bologna as part of his Marie Curie research project BITMAP . He was joined by colleagues from the CNR-IOM of Trieste, the Ca’ Foscari University of Venice, the University of Milan, the University of Wrzburg (Germany), the University of St. Andrews (UK) , Boston College and the University of Santa Barbara (USA).

Through advanced experimental techniques, using the light generated by a particle accelerator, the synchrotron, and thanks to modern techniques for modeling the behavior of matter, scholars have been able to measure for the first time the spin of the electron, linked to the topology concept.

“If we take two objects like a soccer ball and a donut, we notice that their specific shapes determine different topological properties, for example because the donut has a hole, while the ball doesn’t,” explains Domenico Di Sante. “Similarly, the behavior of electrons in materials is influenced by some quantum properties that determine their rotation in the matter in which they are located, similarly to how the trajectory of light in the universe is modified by the presence of stars, black holes, matter and dark energy, which bend time and space.”

Although this characteristic of electrons has been known for many years, no one has been able to measure this “topological spin” directly until now. To achieve this, the researchers exploited a particular effect known as “circular dichroism”: a particular experimental technique that can only be used with a synchrotron source, which exploits the ability of materials to absorb light in different ways depending on their polarization.

Scholars have focused in particular on “kagome materials”, a class of quantum materials that owe their name to their resemblance to the weaving of woven bamboo threads that make up a traditional Japanese basket (called “kagome”). . These materials are revolutionizing quantum physics and the results obtained could help us better understand their special magnetic, topological and superconducting properties.

“These important results were possible thanks to a strong synergy between experimental practice and theoretical analysis”, adds Di Sante. ‘The theoretical researchers in the team employed sophisticated quantum simulations, which are only possible with the use of powerful supercomputers, and in doing so guided their experimental colleagues to the specific area of ​​the material where the effect of circular dichroism could be measured. “.

More information:
Domenico Di Sante et al, Flat Band Separation and Strong Spin Berry Curvature in Bilayer Kagome Metals, Physics of nature (2023). DOI: 10.1038/s41567-023-02053-z

About the magazine:
Physics of nature

Provided by the University of Bologna

#Quantum #materials #electron #spin #measured #time

Ultra-short light pulses in the shape of a wind-up toy put a new spin on photonics

Ultra-short light pulses in the shape of a wind-up toy put a new spin on photonics

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Synthesize spatiotemporal beams with broadband spectral topological correlations. Credit: Photonics of nature (2023). DOI: 10.1038/s41566-023-01223-y

We’ve all played with a spring toy at least once, but did you know that even light can be shaped like a spring?

An international team of researchers, led by Marco Piccardo, former researcher at the Italian Institute of Technology (IIT) and now Professor at the Physics Department of Tcnico Lisboa and Principal Investigator at the Institute of Engineering for Microsystems and Nanotechnologies ( INESC MN), exploited ultrafast optics and structured light to synthesize in the laboratory a new family of spatiotemporal light beams, known as light sources.

The research was conducted in collaboration between IIT, Politecnico di Milano and Tcnico Lisboa. The discovery has disruptive potential for applications in photonics with complex light, such as time-resolved microscopy (useful, for example, to produce films describing the motion of molecules and viruses), laser-plasma acceleration and free space ( for example, in the atmosphere) optical communications.

The research is published in Photonics of nature.

In ultrafast optics, it is possible to shorten or lengthen the duration of extremely short optical pulses down to a few femtoseconds, or thousandths of billionths of a second, or even produce complex pulses, using a technique known as pulse shaping. A central idea of ​​this principle is that the short laser pulses are composed of a wide range of colours.

Scientists separate a pulse into its constituent colors, which are then separately manipulated and recombined, resulting in a new shape of the laser pulse. While pulse shaping allows the temporal profile of a pulse to be manipulated, there is another set of techniques known as wavefront shaping which allows for spatial structure to be given to light. Light designers have learned to combine these two methods to shape light simultaneously in space and time, bridging ultrafast optics and structured light for entirely new space-time applications.

A paradigm shift in spatiotemporal light shaping

Reporting now in Photonics of nature, Piccardo and his collaborators have introduced a paradigm shift in spatiotemporal light shaping. Unlike conventional modelers that separate different colors along a colored stripe, researchers have now used a special type of diffraction grating with circular symmetry to create a round rainbow of colours.

This is an experiment anyone can try at home: Shining a flashlight on an old CD-ROM and taking a picture with your phone’s camera will capture a round rainbow. Now, replace the flashlight with an ultrashort laser pulse and the CD-ROM with a microstructured diffractive device fabricated in the nanofabrication cleanroom and you’re halfway through the experiment. The second part of the experiment is to use advanced holograms to structure the many colors of light into different corkscrew-shaped optical vortexes.

“This results in a new family of spatiotemporal light beams, evolving on an ultrashort femtosecond timescale with a highly customizable and convoluted light structure,” said Marco Piccardo. “It opens up unprecedented design capabilities in photonics, with many spectral and structural components to address.”

The broadband nature of these new light beams poses new challenges for their characterisation, which the team overcame by developing a powerful reconstruction technique, called hyperspectral holography, which provides complete tomography of complex space-time structures.

“Our technique, which combines holography with Fourier transform spectroscopy, allows a complete characterization of the spatiotemporal profile of complex beams, enabling radically new applications in the study of light-matter interactions,” said Giulio Cerullo, professor at Politecnico of Milan and co-author of the study.

The team showed the unprecedented control their space-time modeler allowed by customizing many properties of the light sources. A beautiful demonstration shows two of these springs dancing together in space and time.

‘We have discovered extremely interesting physics using these beams, which could lead us to a whole new generation of compact accelerators and plasma light sources. This technique is very exciting because it promises to bring these theoretical concepts to the laboratory and to trigger important advances in the laser-plasma physics,” said Jorge Vieira, professor at Tcnico Lisboa and co-author of the study.

Now that it is finally possible to synthesize these light sources in complete freedom in the laboratory, the next natural step will be to bring them into laser-plasma experiments.

“This is a very challenging goal, but the nanophoton fabrication capabilities of INESC MN in Lisbon and the excellent plasma research teams of Tcnico represent an ideal ecosystem to pursue this ambitious research,” said Piccardo. “Combining these advanced space-time beams with intense nonlinear laser-matter interactions could have important fundamental and technological implications.”

More information:
Marco Piccardo et al, Broadband control of spectral topological correlations in spatiotemporal bundles, Photonics of nature (2023). DOI: 10.1038/s41566-023-01223-y

About the magazine:
Photonics of nature

Provided by Tcnico Lisboa

#Ultrashort #light #pulses #shape #windup #toy #put #spin #photonics

Physicists discover “parallel loops” of spin currents in antiferromagnets

Physicists discover "parallel loops" of spin currents in antiferromagnets

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Left: An antiferromagnet can function as parallel electric circuits carrying spin currents Nel. Right: A tunnel junction based on antiferromagnets hosting spin currents Nel can be thought of as an electric circuit with the two ferromagnetic tunnel junctions connected in parallel. Credit: Shao Dingfu

A group of physicists from Hefei Institutes of Physical Science (HFIPS) of the Chinese Academy of Sciences (CAS) has revealed a secret of antiferromagnets, which could accelerate spintronics, a next-generation data storage and processing technology to overcome the bottleneck of modern digital electronics.

This discovery was reported in Physical Review Letters.

Spintronics is a rapidly developing field that uses the spin of electrons within magnetic materials to encode information. Spin-polarized electric currents play a central role in spintronics, due to their ability to manipulate and sense the directions of magnetic moments for writing and reading 1s and 0s. Currently, most spintronic devices are based on ferromagnets, where net magnetizations can efficiently rotate polarized electric currents.

Antiferromagnets, with opposite magnetic moments aligned alternately, are less studied but could hold the promise of even faster and smaller spintronic devices. However, antiferromagnets have zero net magnetization and are therefore commonly believed to carry only neutral spin currents that are useless for spintronics. Although antiferromagnets consist of two antiparallel aligned magnetic sublattices, their properties are believed to be “mediated” with respect to the sublattices making them independent of rotation.

Prof. Shao Ding-Fu, who led the team, has a different view on this research. He envisioned collinear antiferromagnets could function as “electric circuits” with the two magnetic sublattices connected in parallel. With this simple intuitive picture in mind, Prof. Shao and his collaborators theoretically predicted that magnetic sublattices could polarize the electric current locally, thus resulting in the spin-offset currents hidden within the globally spin-neutral current.

He dubbed these staggered spin currents “Nel spin currents” after Louis Nel, a Nobel laureate, who won the prize for his seminal work and discoveries regarding antiferromagnetism.

Spin Nel currents are a unique nature of antiferromagnets that has never been recognized. It is capable of generating useful spin-dependent properties that have previously been considered incompatible with antiferromagnets, such as a spin transfer torque and tunneling magnetoresistance in antiferromagnetic tunnel junctions, crucial for electrical writing and reading of information in antiferromagnetic spintronics .

‘Our work has uncovered a previously unexplored potential of antiferromagnetics and offered a simple solution to achieve efficient reading and writing for antiferromagnetic spintronics,’ said Prof. Shao Ding Fu.

More information:
Ding-Fu Shao et al, Nel Spin Currents in Antiferromagnets, Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.130.216702

About the magazine:
Physical Review Letters

Provided by Hefei Institutes of Physical Science, Chinese Academy of Sciences

#Physicists #discover #parallel #loops #spin #currents #antiferromagnets