Experimental observation of the Brownian spin-locking effect of light scattered from Brownian nanoparticles. a, Experimental set-up for observing the effect. A linearly polarized laser (639 nm) impinges on the sample at normal incidence. The sample is contained in a glass vial with AuNPs suspended in water. The observation path is set at a scattering angle perpendicular to the incident light. The images are captured by the camera using a single lens. Pol., linear polarizer; QWP, quarter-wave plate; Lens, convex lens (f = 80 mm). b, An example of a scanning electron microscope image of the AuNPs with = 250 nm. c, Measured second-order autocorrelation function of the AuNPs using a DLS instrument. The coherence time is τc ≈ 0.7 ms. Credit: Nature Materials (2025). DOI: 10.1038/s41563-025-02413-5

An international research team reports the discovery of "hidden order" in systems that are disordered in space and time. The paper is published in the journal Nature Materials.

The results were achieved by Prof. Erez Hasman from the Faculty of Mechanical Engineering and the Helen Diller Quantum Center at the Technion–Israel Institute of Technology, together with colleagues in China led by Prof. Bo Wang, head of Spin Nanophotonics Group, at the School of Physics and Astronomy, Shanghai Jiao Tong University. Prof. Wang conducted his postdoctoral research in Prof. Hasman’s group and was part of the team behind the development of the spin laser made from two-dimensional materials.

In their paper, the researchers present a new physical phenomenon called the spin locking effect induced by Brownian motion, which enables the detection of spin-order in a physically disordered system.

Spin is one of the fundamental properties of elementary particles, describing their rotation or twist. This is a simplified and somewhat inaccurate metaphor, but it is the common way to describe spin.

Brownian motion, also known as a drunkard’s walk, refers to the random movement of tiny particles (not necessarily atomic in size) suspended in or floating on a liquid. Einstein made this phenomenon famous when he published his findings in 1905.

Until now, it was believed that Brownian motion causes the scattering of photons off particles to be chaotic—that is, unpolarized and incoherent—and so too the spin of the scattered photons.

The researchers set out to test whether, under specific light–matter interaction conditions, spin order could emerge—and found that it could. When they shined laser light on nanometric particles suspended in a liquid at room temperature, they discovered that the photons scattered sideways, beyond the laser’s impact zone, became "locked" in their spin. They demonstrated that this spin locking arises precisely because of the particles’ random movement—their Brownian motion.

This process also allowed the researchers to measure the size of the particles, since the spin-locking effect depends on both particle size and material type, thus revealing information about them.

Prof. Hasman remarks, "Our discovery beautifully illustrates the importance of experimental physics. We have shown that it is precisely the most disordered systems—in both space and time—that hold the key to the emergence of deep order.

"The spin-locking effect in a system undergoing Brownian motion is a previously unknown phenomenon, and we hope and believe that its applications—from nanoparticle characterization to the development of new optical technologies—will make a significant contribution to science and industry in the future."

More information: Xiao Zhang et al, Brownian spin-locking effect, Nature Materials (2025). DOI: 10.1038/s41563-025-02413-5

Citation: Order from chaos: The emergence of photon ‘swirling’ in disordered nanometric systems (2025, December 15) retrieved 15 December 2025 from https://phys.org/news/2025-12-chaos-emergence-photon-swirling-disordered.html

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