A flash of terahertz light makes a magnetic crystal move as though its hidden internal order has suddenly been rearranged. The striking part is that the crystal’s visible symmetry changes and keeps oscillating long after the flash. Intense laser pulses let researchers study quantum behavior that cannot be reached by steady changes such as pressure, voltage, strain, or temperature.

Terahertz light is especially useful because strong-field excitation can selectively drive low-energy, collective motions inside materials, making those motions accessible. Those motions could help reveal new behavior in condensed matter and support future light-based technologies, including a wide range of next-generation photonics.

This study examines an antiferromagnet, where the antiferromagnetic spin configuration breaks inversion symmetry, one of the crystal’s usual symmetries in this material. In this picture, strong terahertz excitation dynamically controls the lattice, selectively giving energy to particular atomic vibrations in the material.

The measurements found symmetry changes as large as the material’s ordinary light signal, along with long-lived, coordinated atomic vibrations in its antiferromagnetic state. The proposed cause is a field-driven rearrangement of electric charge that changes the crystal’s underlying symmetry.

The study also found evidence for a field-induced change from antiferromagnetic to ferrimagnetic order. At low temperature, the light signal shows pronounced oscillations whose size is comparable to the material’s equilibrium signal. Above the magnetic ordering temperature, the later-time signal is featureless.

Two especially clear vibrations appear at 1.7 and 4.5 terahertz. The lower-frequency vibration had not been observed in ordinary equilibrium measurements. As temperature rises, the amplitudes of both vibrations decrease and vanish near the magnetic ordering temperature.

The giant coordinated vibration therefore appears only in the antiferromagnetic phase, showing that the magnetic arrangement enables the terahertz field to couple to it. A terahertz pulse briefly drives the material into patterns that no longer match across its mirror line, and that imbalance persists long enough to oscillate.

The oscillations contain the same two characteristic frequencies as the emitted light, linking the lasting symmetry change to atomic vibrations. This field-driven response gives access to vibrations that ordinary linear measurements cannot see.

The appearance of the 1.7-terahertz vibration is also a direct sign that the magnetic moment is being manipulated dynamically. The combined evidence points toward possible new, long-lived magnetic states, supported by the field’s polarization dependence, the newly visible vibration, and matching theory.

For someone outside the laboratory, the promise is a route toward targeted control of phase changes and switching between magnetic states with strong terahertz fields, rather than relying only on permanent changes to the material. A carefully directed electric field can reshape both atomic motion and magnetic order in this material, suggesting a way to switch magnetic states with light rather than permanently changing temperature, pressure, or voltage.