From Niels Bohr Institute: “Quantum Alchemy: Researchers use laser light to transform metal into magnet” 

University of Copenhagen

Niels Bohr Institute bloc

From Niels Bohr Institute

16 September 2019

Mark Spencer Rudner
Associate Professor
Condensed Matter Physics
Niels Bohr Institutet
rudner@nbi.ku.dk

Maria Hornbek
Journalist
The Faculty of Science
maho@science.ku.dk
+45 22 95 42 83

CONDENSED MATTER PHYSICS: Pioneering physicists from the University of Copenhagen and Nanyang Technological University in Singapore have discovered a way to get non-magnetic materials to make themselves magnetic by way of laser light. The phenomenon may also be used to endow many other materials with new properties.

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Mark Rudner, Niels Bohr Institute, University of Copenhagen

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Asst Prof Justin Song Chien Wen

The intrinsic properties of materials arise from their chemistry — from the types of atoms that are present and the way that they are arranged. These factors determine, for example, how well a material may conduct electricity or whether or not it is magnetic. Therefore, the traditional route for changing or achieving new material properties has been through chemistry.

Now, a pair of researchers from the University of Copenhagen and Nanyang Technological University in Singapore have discovered a new physical route to the transformation of material properties: when stimulated by laser light, a metal can transform itself from within and suddenly acquire new properties.

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“For several years, we have been looking into how to transform the properties of a matter by irradiating it with certain types of light. What’s new is that not only can we change the properties using light, we can trigger the material to change itself, from the inside out, and emerge into a new phase with completely new properties. For instance, a non-magnetic metal can suddenly transform into a magnet,” explains Associate Professor Mark Rudner, a researcher at the University of Copenhagen’s Niels Bohr Institute.

He and colleague Justin Song of Nanyang Technological University in Singapore made the discovery that is now published in Nature Physics. The idea of using light to transform the properties of a material is not novel in itself. But up to now, researchers have only been capable of manipulating the properties already found in a material. Giving a metal its own ‘separate life’, allowing it to generate its own new properties, has never been seen before.

By way of theoretical analysis, the researchers have succeeded in proving that when a non-magnetic metallic disk is irradiated with linearly polarized light, circulating electric currents and hence magnetism can spontaneously emerge in the disk.

Researchers use so-called plasmons (a type of electron wave) found in the material to change its intrinsic properties. When the material is irradiated with laser light, plasmons in the metal disk begin to rotate in either a clockwise or counterclockwise direction. However, these plasmons change the quantum electronic structure of a material, which simultaneously alters their own behavior, catalyzing a feedback loop. Feedback from the plasmons’ internal electric fields eventually causes the plasmons to break the intrinsic symmetry of the material and trigger an instability toward self-rotation that causes the metal to become magnetic.

Technique can produce properties ‘on demand’

According to Mark Rudner, the new theory pries open an entire new mindset and most likely, a wide range of applications:

“It is an example of how the interaction between light and material can be used to produce certain properties in a material ‘on demand’. It also paves the way for a multitude of uses, because the principle is quite general and can work on many types of materials. We have demonstrated that we can transform a material into a magnet. We might also be able to change it into a superconductor or something entirely different,” says Rudner. He adds:

“You could call it 21st century alchemy. In the Middle Ages, people were fascinated by the prospect of transforming lead into gold. Today, we aim to get one material to behave like another by stimulating it with a laser.”

Among the possibilities, Rudner suggests that the principle could be useful in situations where one needs a material to alternate between behaving magnetically and not. It could also prove useful in opto-electronics – where, for example, light and electronics are combined for fiber-internet and sensor development.

The researchers’ next steps are to expand the catalog of properties that can be altered in analogous ways, and to help stimulate their experimental investigation and utilization.

See the full article here .


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Niels Bohr Institute Campus

Niels Bohr Institute (Danish: Niels Bohr Institutet) is a research institute of the University of Copenhagen. The research of the institute spans astronomy, geophysics, nanotechnology, particle physics, quantum mechanics and biophysics.

The Institute was founded in 1921, as the Institute for Theoretical Physics of the University of Copenhagen, by the Danish theoretical physicist Niels Bohr, who had been on the staff of the University of Copenhagen since 1914, and who had been lobbying for its creation since his appointment as professor in 1916. On the 80th anniversary of Niels Bohr’s birth – October 7, 1965 – the Institute officially became The Niels Bohr Institute.[1] Much of its original funding came from the charitable foundation of the Carlsberg brewery, and later from the Rockefeller Foundation.[2]

During the 1920s, and 1930s, the Institute was the center of the developing disciplines of atomic physics and quantum physics. Physicists from across Europe (and sometimes further abroad) often visited the Institute to confer with Bohr on new theories and discoveries. The Copenhagen interpretation of quantum mechanics is named after work done at the Institute during this time.

On January 1, 1993 the institute was fused with the Astronomic Observatory, the Ørsted Laboratory and the Geophysical Institute. The new resulting institute retained the name Niels Bohr Institute.

The University of Copenhagen (UCPH) (Danish: Københavns Universitet) is the oldest university and research institution in Denmark. Founded in 1479 as a studium generale, it is the second oldest institution for higher education in Scandinavia after Uppsala University (1477). The university has 23,473 undergraduate students, 17,398 postgraduate students, 2,968 doctoral students and over 9,000 employees. The university has four campuses located in and around Copenhagen, with the headquarters located in central Copenhagen. Most courses are taught in Danish; however, many courses are also offered in English and a few in German. The university has several thousands of foreign students, about half of whom come from Nordic countries.

The university is a member of the International Alliance of Research Universities (IARU), along with University of Cambridge, Yale University, The Australian National University, and UC Berkeley, amongst others. The 2016 Academic Ranking of World Universities ranks the University of Copenhagen as the best university in Scandinavia and 30th in the world, the 2016-2017 Times Higher Education World University Rankings as 120th in the world, and the 2016-2017 QS World University Rankings as 68th in the world. The university has had 9 alumni become Nobel laureates and has produced one Turing Award recipient