Subterahertz collective dynamics of polar vortices

TL;DR

This paper uncovers ultrafast collective polarization dynamics in polar vortices at subterahertz frequencies, revealing a new soft mode called vortexon, with potential for high-speed, high-density data processing applications.

Contribution

It introduces the discovery of a novel soft mode, vortexon, in polar vortices, and demonstrates their ultrafast collective dynamics using terahertz excitation and advanced modeling.

Findings

Observation of ultrafast collective polarization dynamics in polar vortices.

Identification of a new soft mode, vortexon, with picosecond vorticity reversal.

Frequency reduction at critical strain indicating structural dynamic condensation.

Abstract

The collective dynamics of topological structures have been of great interest from both fundamental and applied perspectives. For example, the studies of dynamical properties of magnetic vortices and skyrmions not only deepened the understanding of many-body physics but also led to potential applications in data processing and storage. Topological structures constructed from electrical polarization rather than spin have recently been realized in ferroelectric superlattices, promising for ultrafast electric-field control of topological orders. However, little is known about the dynamics of such complex extended nanostructures which in turn underlies their functionalities. Using terahertz-field excitation and femtosecond x-ray diffraction measurements, we observe ultrafast collective polarization dynamics that are unique to polar vortices, with orders of magnitude higher frequencies and smaller lateral size than those of experimentally realized magnetic vortices. A previously unseen soft mode, hereafter referred to as a vortexon, emerges as transient arrays of nanoscale circular patterns of atomic displacements, which reverse their vorticity on picosecond time scales. Its frequency is significantly reduced at a critical strain, indicating a condensation of structural dynamics. First-principles-based atomistic calculations and phase-field modeling reveal the microscopic atomic arrangements and frequencies of the vortex modes. The discovery of subterahertz collective dynamics in polar vortices opens up opportunities for applications of electric-field driven data processing in topological structures with ultrahigh speed and density.