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Physikgebäude (Neubau Otto-Hahn-Str. 4a) an der TU Dortmund © Nikolas Golsch​/​TU Dortmund

When Spins Synchronize: Time Crystals in Action

Start: End: Location: Hörsaalgebäude II, Hörsaal 2
Event type:
  • Colloquium
Fig. 1. a- Periodic oscillations of electron spin polarization. At the bottom, different views of the 3-dimensional phase space plot of the limit cycle. Black points mark the recorded data. b- Measured contour plot of fast Fourier (FFT) spectra for the modulated version of the system as a function of the inverse modulation frequency fm. It demonstrates different regimes, including synchronization (horizontal plateaus), bifurcation jets, and chaos. The color scheme on the right indicates the normalized amplitude of the Faraday rotation. f0 – is the first own harmonic of the unmodulated oscillations. fexp – observed FFT frequencies. © Alex Greilich​/​TU Dortmund
Fig. 1. a- Periodic oscillations of electron spin polarization. At the bottom, different views of the 3-dimensional phase space plot of the limit cycle. Black points mark the recorded data. b- Measured contour plot of fast Fourier (FFT) spectra for the modulated version of the system as a function of the inverse modulation frequency fm. It demonstrates different regimes, including synchronization (horizontal plateaus), bifurcation jets, and chaos. The color scheme on the right indicates the normalized amplitude of the Faraday rotation. f0 – is the first own harmonic of the unmodulated oscillations. fexp – observed FFT frequencies.
Lecture in the colloquium of PD Dr. Alex Greilich
PD Dr. Alex Greilich, TU Dortmund

When Spins Synchronize: Time Crystals in Action

Nonlinear dynamics govern many of the most captivating phenomena in nature — from the rhythmic beating of the heart to the turbulent flow of fluids, from synchronized fireflies to the unpredictable beauty of chaos. These systems can self-organize, oscillate, synchronize, or spiral into instability, often revealing intricate patterns out of simplicity. How remarkable would it be to recreate and study such rich dynamical behavior in a well-controlled, solid-state environment?

In this colloquium, I will present how a dissipative electron-nuclear spin system in a semiconductor gives rise to robust, self-sustained auto-oscillations under continuous optical excitation. These oscillations, appearing across a wide range of laser powers, temperatures, and magnetic fields, form stable limit cycles with coherence times extending to hours [1]. When the system is periodically driven by modulating excitation power or polarization, it reveals hallmark features of nonlinear dynamics: frequency entrainment, subharmonic bifurcations, and a devil’s staircase of resonances. Chaotic dynamics emerge as the system nears synchronization thresholds, uncovering a detailed picture of the boundary between order and disorder [2].

This platform provides not only a novel approach to studying complex, collective behavior in semiconductors but also a compelling parallel to the concept of time-matter organization. The structured oscillatory response—spontaneous, long-lived, and richly tunable—evokes the essence of time-crystalline phenomena but is grounded in a classical nonlinear landscape.

 

References

[1] A. Greilich, N. E. Kopteva, A. N. Kamenskii, P. S. Sokolov, V. L. Korenev, and M. Bayer, Nature Physics 20, 631 (2024).

[2] A. Greilich, N. E. Kopteva, V. L. Korenev, Ph. A. Haude, and M. Bayer, Nature Commun. 16, 2936 (2025).

 

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