AsianScientist (Aug. 23, 2019) – Scientists in Singapore and Denmark have found theoretical evidence for turning a non-magnetic metal into a magnet using laser light. Their findings are published in the journal Nature Physics.
Magnets and their magnetic field are typically produced by circulating currents, like those found in everyday electromagnetic coils. The ‘handedness’ of these coils—whether they are wound in a clockwise or anticlockwise fashion—determines the direction of the magnetic field produced.
In the present study, scientists led by Assistant Professor Justin at Nanyang Technological University, Singapore, and Associate Professor Mark Rudner at the University of Copenhagen, Denmark, theorized that magnetism can be induced in metal using just light.
To do so, they studied plasmons—local oscillations of charge in metals—and the intense oscillating electric fields they create. Plasmons tend to oscillate and move in the same direction as the field that is driving them, for example, the polarization direction of a light field.
The researchers proposed that when a non-magnetic metallic disk is exposed to sufficiently intense light irradiation, the plasmons in the disk spontaneously rotate in either a left-handed or right-handed fashion, even when driven by linearly polarized light. This then triggers spontaneous magnetism in the metallic disk.
The team noted that the key observation in their theoretical analysis is that intense plasmonic oscillating electric fields can modify the dynamics of electrons in the metal.
“From the point of view of an electron within a material, an electric field is an electric field: it doesn’t matter whether this oscillating field was produced from plasmons within the material itself or by a laser shining on the material,” said Rudner.
“Perhaps the most meaningful take-home message of our work is that it shows that collective modes can exhibit distinct new phases. If plasmonic magnetism is possible, what other phases of collective modes are waiting to be uncovered?” Song added.
The article can be found at: Rudner & Song (2019) Self-induced Berry Flux and Spontaneous Non-equilibrium Magnetism.
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Source: Nanyang Technological University.
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