Finding Pattern in Randomness: Brownian Motion of Skyrmions
© The Physical Society of Japan
This article is on
Brownian Motion of Magnetic Skyrmions in One- and Two-Dimensional Systems
(JPSJ Editors' Choice)
J. Phys. Soc. Jpn. 90, 083601 (2021).
The chiral properties of the Brownian motion of magnetic skyrmions in one- and two-dimensional systems in thermal equilibrium are reported.
Magnetic skyrmions exhibit unique dynamical properties. However, it is unclear whether the Brownian motion of skyrmions exhibits chiral properties in thermal equilibrium derived from the Magnus force. For example, when a skyrmion is driven by an electric current, the driving force is parallel to the current. However, its trajectory is bent by the Magnus force, which is proportional to the skyrmion number. Consequently, the skyrmion Hall effect is observed. Such chiral motion of skyrmions has been observed in the presence of a driving force. However, whether the Brownian motion of skyrmions exhibits chiral properties in thermal equilibrium remains unclear. (Note that the chiral property in this study is not that of skyrmions but of their motion.) In this study, we show that chiral properties play an essential role in the diffusion of skyrmions by performing the following two experiments:
Diffusion of skyrmions in one-dimensional and two-dimensional channels
The diffusion coefficient of skyrmions in one-dimensional narrow channels is a factor of 1.3–1.9 larger than that in two-dimensional films. This is because the confinement of skyrmions in one-dimensional channels suppresses their gyration.
Observation of angular momentum of diffusion in two-dimensional systems
We evaluated chiral properties by analyzing the diffusion of skyrmions using the spontaneous velocity–position correlation functions, i.e., <v(t)・x(t)> and <(v(t) × x(t))z> [1], and obtained the finite value of <(v(t)×x(t))z> as a thermal average. This result indicates the existence of the off-diagonal term of the diffusion coefficient of the skyrmions' motion. In addition, the sign of the observed <(v(t)×x(t))z> is opposite to the sign of the simple theoretical prediction, i.e., the direction of rotation is opposite to that predicted by theory. This can be explained by considering the shallow potential fluctuation in the films. The orbit of skyrmions captured by the harmonic potential was a hypotrochoid, a combination of two circular motions, with thermal fluctuation. The small, high-frequency circular motion was the intrinsic gyration of skyrmions. In contrast, a low-frequency orbit that rotated along the edge of the potential exhibited reverse rotation. Because the camera's frame rate was set at 30 ms−1 in the experiments, only the global rotation in the direction opposite to that of the local gyration was observed. The observation of the intrinsic gyration and mass of skyrmions under Brownian motion should be examined in the future [2].
(Written by S. Miki on behalf of all authors)
References
[1] Y. Suzuki, S. Miki, Y. Imai, and E. Tamura, Phys. Lett. A, 413, 127603 (2021), and references therein.
[2] I. Makhfudz, B. Krüger, and O. Tchernyshyov, Phys. Rev. Lett. 109, 217201 (2012).
Brownian Motion of Magnetic Skyrmions in One- and Two-Dimensional Systems
(JPSJ Editors' Choice)
J. Phys. Soc. Jpn. 90, 083601 (2021).
Share this topic
Fields
Related Articles
-
Chiral Anomalies in Organic Dirac Semimetals
Electronic transport in condensed matter
2024-2-5
A three-dimensional massless Dirac fermion system exhibiting broken chiral symmetry was successfully realized in organic conductor α-(BEDT-TTF)2I3 under high pressures. Our study detected the chiral anomaly-induced negative magnetoresistance and planar Hall effects and opened new avenues for further advancements in the field.
-
Relation between Mean-Field Theory and Atomic Structures in Chalcogenide Glasses
Structure and mechanical and thermal properties in condensed matter
2024-2-1
The authors conducted various of X-ray and neutron scattering experiments on typical chalcogenide glasses and clarified the relationship between the atomic structure and simple rigidity percolation theory.
-
Thermodynamic Property of a CMOS Device beyond Landauer Limit
Statistical physics and thermodynamics
Electronic transport in condensed matter
Cross-disciplinary physics and related areas of science and technology
2024-1-23
Focusing on a CMOS NAND GATE operating in a sub-threshold region, the thermodynamic cost of computation was analyzed in relation to input/output voltages surpassing the Landauer limit.
-
Current Melt Frozen Electrons
Dielectric, optical, and other properties in condensed matter
Magnetic properties in condensed matter
2024-1-15
The origin of the current-induced insulator-to-metal transition of samarium monosulfide was explained by the 4f−5d hybridization observed using optical reflectivity and photoelectron spectroscopies.
-
Towards Uncovering the Hidden Order of URu2Si2 Phase Transition
Magnetic properties in condensed matter
Electronic structure and electrical properties of surfaces and nanostructures
2024-1-11
We propose a chiral charge as the hidden order parameter in URu2Si2 and present experiments to detect it by focusing on breakings of mirror and inversion symmetries at the local uranium ion.