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Photoinduced twist and untwist of moiré superlattices in TMDC heterobilayers
Authors:
C. J. R. Duncan,
A. C. Johnson,
I. Maity,
A. Rubio,
M. Gordon,
A. C. Bartnik,
M. Kaemingk,
W. H. Li,
M. B. Andorf,
C. A. Pennington,
I. V. Bazarov,
M. W. Tate,
D. A. Muller,
J. Thom-Levy,
S. M. Gruner,
A . M. Lindenberg,
F. Liu,
J. M. Maxson
Abstract:
Two-dimensional moiré materials are formed by artificially stacking atomically thin monolayers. A wealth of correlated and topological quantum phases can be engineered via precise choice of stacking geometry. These designer electronic properties depend crucially on interlayer coupling and atomic registry. An important open question is how atomic registry responds on ultrafast timescales to optical…
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Two-dimensional moiré materials are formed by artificially stacking atomically thin monolayers. A wealth of correlated and topological quantum phases can be engineered via precise choice of stacking geometry. These designer electronic properties depend crucially on interlayer coupling and atomic registry. An important open question is how atomic registry responds on ultrafast timescales to optical excitation and whether the moiré geometry can be dynamically reconfigured to tune emergent phenomena in real time. Here we show that femtosecond photoexcitation drives a coherent twist-untwist motion of the moiré superlattice in $2^\circ$ and $57^\circ$ twisted WSe$_2$/MoSe$_2$ heterobilayers, resolved directly by ultrafast electron diffraction. Upon above-band-gap photoexcitation, the moiré superlattice diffraction features are enhanced within 1 ps and subsequently suppressed several picoseconds after, deviating markedly from typical photoinduced lattice heating. Kinetic diffraction analysis, supported by simulations of the sample dynamics, indicates a peak-to-trough local twist angle modulation of $0.6^\circ$, correlated with a sub-THz frequency moiré phonon. This motion is driven by ultrafast charge transfer that transiently increases interlayer attraction. Our results could lead to ultrafast control of moiré periodic lattice distortions and, by extension, the local moiré potential that shapes excitons, polarons, and correlation-driven behaviors
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Submitted 22 October, 2025; v1 submitted 17 February, 2025;
originally announced February 2025.
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Multi-scale time-resolved electron diffraction: A case study in moiré materials
Authors:
C. J. R. Duncan,
M. Kaemingk,
W. H. Li,
M. B. Andorf,
A. C. Bartnik,
A. Galdi,
M. Gordon,
C. A. Pennington,
I. V. Bazarov,
H. J. Zeng,
F. Liu,
D. Luo,
A. Sood,
A. M. Lindenberg,
M. W. Tate,
D. A. Muller,
J. Thom-Levy,
S. M. Gruner,
J. M. Maxson
Abstract:
Ultrafast-optical-pump -- structural-probe measurements, including ultrafast electron and x-ray scattering, provide direct experimental access to the fundamental timescales of atomic motion, and are thus foundational techniques for studying matter out of equilibrium. High-performance detectors are needed in scattering experiments to obtain maximum scientific value from every probe particle. We dep…
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Ultrafast-optical-pump -- structural-probe measurements, including ultrafast electron and x-ray scattering, provide direct experimental access to the fundamental timescales of atomic motion, and are thus foundational techniques for studying matter out of equilibrium. High-performance detectors are needed in scattering experiments to obtain maximum scientific value from every probe particle. We deploy a hybrid pixel array direct electron detector to perform ultrafast electron diffraction experiments on a WSe$_2$/MoSe$_2$ 2D heterobilayer, resolving the weak features of diffuse scattering and moiré superlattice structure without saturating the zero order peak. Enabled by the detector's high frame rate, we show that a chopping technique provides diffraction difference images with signal-to-noise at the shot noise limit. Finally, we demonstrate that a fast detector frame rate coupled with a high repetition rate probe can provide continuous time resolution from femtoseconds to seconds, enabling us to perform a scanning ultrafast electron diffraction experiment that maps thermal transport in WSe$_2$/MoSe$_2$ and resolves distinct diffusion mechanisms in space and time.
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Submitted 27 July, 2023; v1 submitted 16 June, 2022;
originally announced June 2022.
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Dynamics of antiferromagnetic skyrmion in absence and presence of pinning defect
Authors:
Z. Jin,
T. T. Liu,
W. H. Li,
X. M. Zhang,
Z. P. Hou,
D. Y. Chen,
Z. Fan,
M. Zeng,
X. B. Lu,
X. S. Gao,
M. H. Qin,
J. M. Liu
Abstract:
A theoretical study on the dynamics of an antiferromagnetic (AFM) skyrmion is indispensable for revealing the underlying physics and understanding the numerical and experimental observations. In this work, we present a reliable theoretical treatment of the spin current induced motion of an AFM skyrmion in the absence and presence of pinning defect. For an ideal AFM system free of defect, the skyrm…
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A theoretical study on the dynamics of an antiferromagnetic (AFM) skyrmion is indispensable for revealing the underlying physics and understanding the numerical and experimental observations. In this work, we present a reliable theoretical treatment of the spin current induced motion of an AFM skyrmion in the absence and presence of pinning defect. For an ideal AFM system free of defect, the skyrmion motion velocity as a function of the intrinsic parameters can be derived, based on the concept that the skyrmion profile agrees well with the 360 domain wall formula, leading to an explicit description of the skyrmion dynamics. However, for an AFM lattice containing a defect, the skyrmion can be pinned and the depinning field as a function of damping constant and pinning strength can be described by the Thiele approach. It is revealed that the depinning behavior can be remarkably influenced by the time dependent oscillation of the skyrmion trajectory. The present theory provides a comprehensive scenario for manipulating the dynamics of AFM skyrmion, informative for future spintronic applications based on antiferromagnets.
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Submitted 28 July, 2020;
originally announced July 2020.
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Ultralow-loss domain wall motion driven by magnetocrystalline anisotropy gradient in antiferromagnetic nanowire
Authors:
D. L. Wen,
Z. Y. Chen,
W. H. Li,
M. H. Qin,
D. Y. Chen,
Z. Fan,
M. Zeng,
X. B. Lu,
X. S. Gao,
J. M. Liu
Abstract:
Searching for new methods controlling antiferromagnetic (AFM) domain wall is one of the most important issues for AFM spintronic device operation. In this work, we study theoretically the domain wall motion of an AFM nanowire, driven by the axial anisotropy gradient generated by external electric field, allowing the electro control of AFM domain wall motion in the merit of ultra-low energy loss. T…
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Searching for new methods controlling antiferromagnetic (AFM) domain wall is one of the most important issues for AFM spintronic device operation. In this work, we study theoretically the domain wall motion of an AFM nanowire, driven by the axial anisotropy gradient generated by external electric field, allowing the electro control of AFM domain wall motion in the merit of ultra-low energy loss. The domain wall velocity depending on the anisotropy gradient magnitude and intrinsic material properties is simulated based on the Landau-Lifshitz-Gilbert equation and also deduced using the energy dissipation theorem. It is found that the domain wall moves at a nearly constant velocity for small gradient, and accelerates for large gradient due to the enlarged domain wall width. The domain wall mobility is independent of lattice dimension and types of domain wall, while it is enhanced by the Dzyaloshinskii-Moriya interaction. In addition, the physical mechanism for much faster AFM wall dynamics than ferromagnetic wall dynamics is qualitatively explained. This work unveils a promising strategy for controlling the AFM domain walls, benefiting to future AFM spintronic applications.
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Submitted 10 September, 2019; v1 submitted 16 May, 2019;
originally announced May 2019.
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Skyrmion crystals in frustrated Shastry-Sutherland magnets
Authors:
J. H. Yu,
W. H. Li,
Z. P. Huang,
J. J. Liang,
J. Chen,
D. Y. Chen,
Z. P. Hou,
M. H. Qin
Abstract:
The phase diagrams of the frustrated classical spin model with Dzyaloshinskii-Moriya (DM) interaction on the Shastry-Sutherland (S-S) lattice are studied by means of Monte Carlo simulation. For ferromagnetic next-nearest-neighboring (J2) interactions, the introduced exchange frustration enhances the effect of the DM interaction, which enlarges the magnetic field-range with the skyrmion lattice pha…
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The phase diagrams of the frustrated classical spin model with Dzyaloshinskii-Moriya (DM) interaction on the Shastry-Sutherland (S-S) lattice are studied by means of Monte Carlo simulation. For ferromagnetic next-nearest-neighboring (J2) interactions, the introduced exchange frustration enhances the effect of the DM interaction, which enlarges the magnetic field-range with the skyrmion lattice phase and increases the skyrmion density. For antiferromagnetic J2 interactions, the so-called 2q phase (two-sublattice skyrmion crystal) and the spin-flop phase are observed in the simulated phase diagram, and their stabilizations are closely dependent on the DM interaction and J2 interaction, respectively. The simulated results are qualitatively explained from the energy landscape, which provides useful information for understanding the intriguing phases in S-S magnets.
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Submitted 30 October, 2018;
originally announced October 2018.