New electron microscopy technique reveals complex spin structures on femtosecond timescales

Plasmons are collective oscillations of electrons in solids and are important for a wide range of applications such as sensing, catalysis, and light harvesting. Plasmon waves that travel along the surface of metals, called surface plasmon polaritons, have been studied for their ability to enhance electromagnetic fields.

One of the most powerful tools for studying these waves is time-resolved electron microscopy, which uses ultrashort laser pulses to observe how these plasmonic waves behave. An international research team recently pushed the boundaries of this technology.

As reported in Advanced Photonics, the researchers used multiple time-delayed laser pulses of four different polarizations to capture the entire electric field of these waves. This method allowed us to achieve a level of accuracy that was previously impossible.

To test their technique, the team investigated a particular spin texture known as melonpear. Melons are topological structures in which the direction of the spin texture covers only half of the sphere, distinguishing them from other similar structures such as skyrmions, in which the spins cover the entire sphere.

To reconstruct the spin texture from the experiment, the researchers needed the electric and magnetic field vectors of the surface plasmon polariton. While the electric field vector could be measured directly, the magnetic field vector had to be calculated based on the behavior of the electric field over time and space.

Using their precise method, the researchers were able to reconstruct the spin texture and determine topological properties such as the Churn number, which is the number of times the spin texture is mapped onto the sphere. In this case, the churn number was found to be 1, indicating the presence of a melon pair.

This study also demonstrated that the spin texture remains stable throughout the duration of the plasmonic pulse despite the fast rotation of the electric and magnetic field vectors. This new approach is not limited to melon pairs but can also be applied to other complex surface plasmon polariton fields.

Understanding these fields and their topological properties is important, especially at the nanoscale, where topological protection can help maintain the stability of materials and devices.

This study shows that it is now possible to study complex spin textures with high precision on extremely short time scales. The ability to precisely reconstruct the complete electric and magnetic fields of surface plasmon polaritons offers new possibilities to explore the topological properties of electromagnetic near-fields, which may have important implications for future technologies at the nanoscale. There is.