Abstract
Skyrmions are topologically protected, vortexlike formations of a field that cannot be removed by any smooth transformation and emerge in a range of fundamentally different, either quantum or classical systems, from spin textures to chiral ferromagnets and chiral complex fluids. Notably, they are generally observed in thin ordered or disordered quasi-2D layers, but little is known about their three-dimensional structuring and organization, including structural transitions from 2D to 3D. Here, we show experimentally and numerically that the blue phase (BP) III of a chiral liquid crystal is a 3D fluid of chiral skyrmion filaments of the nematic orientational field, entangled with a 3D network of topological defect lines. It is an effective 3D dynamic fluid determined by the thermal fluctuations of two distinct branches of excitations: rapid internal fluctuations of the skyrmion structure and a slow collective motion of the skyrmion filaments. When confined to less than an approximately 150-nm layer, the 3D bulk skyrmion fluid transforms into a different effectively 2D liquid of half-skyrmions, with the dynamics of the skyrmion liquid slowing down by an order of magnitude and with the individual skyrmions lingering, and even disappearing into, and reappearing from the homogeneous liquid crystal. The thickness-temperature phase diagram actually shows that both the BPIII and BPI phases are made of skyrmions, which when confined to less than approximately 150 nm cells transform equally into a 2D half-skyrmion liquid. The temperature range of this 2D half-skyrmion liquid is much broader than the temperature interval of BP phases, which makes BP materials interesting for broad-temperature-range skyrmionic applications. We envisage a soft matter skyrmionic device, in which skyrmions are created and detected by light.
- Received 26 July 2021
- Revised 12 October 2021
- Accepted 12 November 2021
DOI:https://doi.org/10.1103/PhysRevX.12.011003
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Skyrmions are vortexlike patterns in a material, similar to the circular flow patterns seen in hurricanes. Magnetic skyrmions, for example, are nanometer-sized whirls of atomic magnets, which researchers are extensively studying for applications in information storage. However, magnetic skyrmions are difficult to make at room temperature. Here, we study another class of skyrmions, formed in room-temperature liquids called blue phases, which we find may be competitive with, if not superior to, magnetic skyrmions for information storage.
Blue phases are ordered liquids: Unlike in water, the molecules of a blue phase are locally aligned in one direction. Because the molecules are chiral—the molecules prefer one of two possible shapes that are mirror images of one another—they can spontaneously form circular patterns, or skyrmions.
For the three different blue phases, we show, using an optical microscope, that they are all formed of skyrmion filaments. These filaments are like long ropes, with a cross section of a vortex, whirling from the center to the periphery. In particular, we show that blue phase III consists of a random and highly dynamic network of skyrmion filaments, which are clearly resolved in microscope images in very thin layers of this material. The skyrmions in such thin layers indeed look like objects carrying bits of information.
The broad temperature range over which blue phases are stable could make them intriguing platforms for “soft matter skyrmionic devices,” where information-storing skyrmions are created and detected with light.
