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Nanoimprinted topological laser in the visible
Authors:
Qiang Zhang,
Rui Duan,
Yutian Ao,
Lin Wang,
Xuehong Zhou,
Xuyong Yang,
Xiao-Cong Yuan,
Baile Zhang,
Handong Sun
Abstract:
Nanoimprint lithography (NIL) is a widely used high-throughput fabrication technique for photonic devices, yet its reliability is often compromised by the inevitable imperfections that arise during the demolding process. Topological photonics, which harnesses topologically nontrivial structures to support defect-robust photonic states, offers a promising solution to this challenge. Here, we demons…
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Nanoimprint lithography (NIL) is a widely used high-throughput fabrication technique for photonic devices, yet its reliability is often compromised by the inevitable imperfections that arise during the demolding process. Topological photonics, which harnesses topologically nontrivial structures to support defect-robust photonic states, offers a promising solution to this challenge. Here, we demonstrate a topological laser that is one-step nanoimprinted upon colloidal perovskite nanocrystals. This laser features multiple higher-order topological corner states, with topological protection provided by the structure effectively mitigating imperfections caused by the nanoimprinting process. This property enables the reliable detection of these states, which is particularly challenging to achieve in the visible spectrum. Our work establishes topological photonics as a viable pathway to enhance the reliability of NIL-based manufacturing, providing a scalable and practical route for mass-producing topological lasers with low-index materials.
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Submitted 25 September, 2025;
originally announced September 2025.
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Electric-field Control of Giant Ferronics
Authors:
Baolong Zhang,
Ruihuan Duan,
Sobhan Subhra Mishra,
Sambhu Jana,
Jonghyeon Kim,
Thomas Tan Caiwei,
Yi Ji Tan,
Wenhao Wang,
Pang Teng Chen Ietro,
Zheng Liu,
Ranjan Singh
Abstract:
Ferrons are quantum excitations of electric polarization in ferroelectrics and electric analogues of magnons but have lacked direct experimental verification at room temperature. We harness the coupling of soft phonons and ferroelectric order in layered NbOX2 (X = I, Br, Cl) to generate, detect, and control giant ferrons, creating a new class of ultralow-power, chip-scale terahertz (THz) sources.…
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Ferrons are quantum excitations of electric polarization in ferroelectrics and electric analogues of magnons but have lacked direct experimental verification at room temperature. We harness the coupling of soft phonons and ferroelectric order in layered NbOX2 (X = I, Br, Cl) to generate, detect, and control giant ferrons, creating a new class of ultralow-power, chip-scale terahertz (THz) sources. Multiple ferron modes produce intense, narrowband THz emission with quality factors up to 228 and radiation efficiencies up to five orders of magnitude greater than state of the art semiconductor emitters. Resonant excitation of a high-Q ferron mode achieves efficiencies two orders of magnitude higher than intense lithium niobate THz sources. We further demonstrate direct, non-volatile electric-field control of ferron oscillations. These findings provide evidence for multiple ferrons and establish Ferronics as a foundational platform for light- and field-driven control of quantum order, with broad impact on ultrafast electronics, photonics, quantum technologies, and next-generation wireless communication.
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Submitted 7 September, 2025;
originally announced September 2025.
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Optical Switching of Moiré Chern Ferromagnet
Authors:
Xiangbin Cai,
Haiyang Pan,
Yuzhu Wang,
Abdullah Rasmita,
Shunshun Yang,
Yan Zhao,
Wei Wang,
Ruihuan Duan,
Ruihua He,
Kenji Watanabe,
Takashi Taniguchi,
Zheng Liu,
Jesús Zúñiga Pérez,
Bo Yang,
Weibo Gao
Abstract:
Optical manipulation of quantum matter offers a non-contact, high-precision and fast control. Fractional Chern ferromagnet states in moiré superlattices are promising for topological quantum computing, but an effective optical control protocol has remained elusive. Here, we demonstrate robust optical switching of integer and fractional Chern ferromagnets in twisted MoTe2 bilayers using circularly…
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Optical manipulation of quantum matter offers a non-contact, high-precision and fast control. Fractional Chern ferromagnet states in moiré superlattices are promising for topological quantum computing, but an effective optical control protocol has remained elusive. Here, we demonstrate robust optical switching of integer and fractional Chern ferromagnets in twisted MoTe2 bilayers using circularly polarized light. Highly efficient optical manipulation of spin orientations in the topological ferromagnet regime is realized at zero field using a pump light power as low as 28 nanowatts per square micrometer. Utilizing this optically induced transition, we also demonstrate magnetic bistate cycling and spatially resolved writing of ferromagnetic domain walls. This work establishes a reliable and efficient optical control scheme for moiré Chern ferromagnets, paving the way for dissipationless spintronics and quantized Chern junction devices.
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Submitted 27 August, 2025;
originally announced August 2025.
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Strain Induced Robust Skyrmion lattice at Room Temperature in van der Waals Ferromagnet
Authors:
Xinyi Zhou,
Iftikhar Ahmed Malik,
Ruihuan Duan,
Hanqing Shi,
Chen Liu,
Yan Luo,
Yue Sun,
Ruixi Chen,
Yilin Liu,
Shian Xia,
Vanessa Li Zhang,
Sheng Liu,
Chao Zhu,
Xixiang Zhang,
Yi Du,
Zheng Liu,
Ting Yu
Abstract:
Manipulating topological magnetic orders of two-dimensional (2D) magnets by strain, once achieved, offers enormous potential for future low-power flexible spintronic applications. In this work, by placing Fe3GaTe2 (FGaT), a room-temperature 2D ferromagnet, on flexible substrate, we demonstrate a field-free and robust formation of skyrmion lattice induced by strain. By applying a minimal strain of…
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Manipulating topological magnetic orders of two-dimensional (2D) magnets by strain, once achieved, offers enormous potential for future low-power flexible spintronic applications. In this work, by placing Fe3GaTe2 (FGaT), a room-temperature 2D ferromagnet, on flexible substrate, we demonstrate a field-free and robust formation of skyrmion lattice induced by strain. By applying a minimal strain of ~0.80% to pre-annealed FGaT flakes, the Magnetic Force Microscopy (MFM) tip directly triggers the transition from maze-like domains to an ordered skyrmion lattice while scanning the sample surface. The skyrmion lattice is rather stable against extensive cyclic mechanical testing (stretching, bending, and twisting over 2000 cycles each). It also exhibited stability across a wide range of magnetic fields (~2.9 kOe) and temperatures (~ 323 K), as well as long-term retention stability, highlighting its robustness and field free stabilization. The strain effect reduces the lattice symmetry and enhances the Dzyaloshinskii-Moriya interaction (DMI) of FGaT, thus stabilizing the skyrmion lattice. Our findings highlight the potential of FGaT for integrating magnetic skyrmions into future low-power-consumption flexible spintronics devices.
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Submitted 13 May, 2025;
originally announced May 2025.
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Room-temperature tunable tunneling magnetoresistance in Fe3GaTe2/WSe2/Fe3GaTe2 van der Waals heterostructures
Authors:
Haiyang Pan,
Anil Kumar Singh,
Chusheng Zhang,
Xueqi Hu,
Jiayu Shi,
Liheng An,
Naizhou Wang,
Ruihuan Duan,
Zheng Liu,
S tuart S. P. Parkin,
Pritam Deb,
Weibo Gao
Abstract:
The exceptional properties of two-dimensional (2D) magnet materials present a novel approach to fabricate functional magnetic tunnel junctions (MTJ) by constructing full van der Waals (vdW) heterostructures with atomically sharp and clean interfaces. The exploration of vdW MTJ devices with high working temperature and adjustable functionalities holds great potential for advancing the application o…
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The exceptional properties of two-dimensional (2D) magnet materials present a novel approach to fabricate functional magnetic tunnel junctions (MTJ) by constructing full van der Waals (vdW) heterostructures with atomically sharp and clean interfaces. The exploration of vdW MTJ devices with high working temperature and adjustable functionalities holds great potential for advancing the application of 2D materials in magnetic sensing and data storage. Here, we report the observation of highly tunable room-temperature tunneling magnetoresistance through electronic means in a full vdW Fe3GaTe2/WSe2/Fe3GaTe2 MTJ. The spin valve effect of the MTJ can be detected even with the current below 1 nA, both at low and room temperatures, yielding a tunneling magnetoresistance (TMR) of 340% at 2 K and 50% at 300 K, respectively. Importantly, the magnitude and sign of TMR can be modulated by a DC bias current, even at room temperature, a capability that was previously unrealized in full vdW MTJs. This tunable TMR arises from the contribution of energy-dependent localized spin states in the metallic ferromagnet Fe3GaTe2 during tunnel transport when a finite electrical bias is applied. Our work offers a new perspective for designing and exploring room-temperature tunable spintronic devices based on vdW magnet heterostructures.
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Submitted 5 June, 2024;
originally announced June 2024.
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Exciton-exciton Interaction in Monolayer MoSe$_2$ from Mutual Screening of Coulomb Binding
Authors:
Ke Xiao,
Tengfei Yan,
Chengxin Xiao,
Feng-ren Fan,
Ruihuan Duan,
Zheng Liu,
Kenji Watanabe,
Takashi Taniguchi,
Wang Yao,
Xiaodong Cui
Abstract:
The potential for low-threshold optical nonlinearity has received significant attention in the fields of photonics and conceptual optical neuron networks. Excitons in two-dimensional (2D) semiconductors are particularly promising in this regard as reduced screening and dimensional confinement foster their pronounced many-body interactions towards nonlinearity. However, experimental determination o…
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The potential for low-threshold optical nonlinearity has received significant attention in the fields of photonics and conceptual optical neuron networks. Excitons in two-dimensional (2D) semiconductors are particularly promising in this regard as reduced screening and dimensional confinement foster their pronounced many-body interactions towards nonlinearity. However, experimental determination of the interactions remains ambiguous, as optical pumping in general creates a mixture of excitons and unbound carriers, where the impacts of band gap renormalization and carrier screening on exciton energy counteract each other. Here by comparing the influences on exciton ground and excited states energies in the photoluminescence spectroscopy of monolayer MoSe$_2$, we are able to identify separately the screening of Coulomb binding by the neutral excitons and by charge carriers. The energy difference between exciton ground state (A-1s) and excited state (A-2s) red-shifts by 5.5 meV when the neutral exciton density increases from 0 to $4\times 10^{11}$ cm$^{-2}$, in contrast to the blue shifts with the increase of either electron or hole density. This energy difference change is attributed to the mutual screening of Coulomb binding of neutral excitons, from which we extract an exciton polarizability of $α_{2D}^{\rm exciton} = 2.55\times 10^{-17}$ eV(m/V)$^2$. Our finding uncovers a new mechanism that dominates the repulsive part of many-body interaction between neutral excitons.
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Submitted 28 August, 2023;
originally announced August 2023.
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Complete Suppression of Phase Segregation in Mixed-Halide Perovskite Nanocrystals under Periodic Heating
Authors:
Shengnan Feng,
Rentong Duan,
Yu Ju,
Shuyi Li,
Chunfeng Zhang,
Shuxia Tao,
Min Xiao,
Xiaoyong Wang
Abstract:
Under continuous light illumination, it is known that localized domains with segregated halide compositions form in semiconducting mixed-halide perovskites, thus severely limiting their optoelectronic applications due to the negative changes in bandgap energies and charge-carrier characteristics. Here we deposit mixed-halide perovskite CsPbBr1.2I1.8 nanocrystals onto an indium tin oxide substrate,…
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Under continuous light illumination, it is known that localized domains with segregated halide compositions form in semiconducting mixed-halide perovskites, thus severely limiting their optoelectronic applications due to the negative changes in bandgap energies and charge-carrier characteristics. Here we deposit mixed-halide perovskite CsPbBr1.2I1.8 nanocrystals onto an indium tin oxide substrate, whose temperature can be rapidly changed by ~10 degree in a few seconds by applying or removing an external voltage. Such a sudden temperature change induces a temporary transition of CsPbBr1.2I1.8 nanocrystals from the segregated phase to the mixed phase, the latter of which can be permanently maintained when the light illumination is coupled with periodic heating cycles. These findings mark the emergence of a practical solution to the detrimental phase-segregation problem, given that a small temperature modulation is readily available in various fundamental studies and practical devices using mixed-halide perovskites.
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Submitted 20 March, 2023;
originally announced March 2023.
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Hybridization and Correlation between f- and d-orbital electrons in a valence fluctuating compound EuNi2P2
Authors:
Z. X. Yin,
X. Du,
W. Z. Cao,
J. Jiang,
C. Chen,
S. R. Duan,
J. S. Zhou,
X. Gu,
R. Z. Xu,
Q. Q. Zhang,
W. X. Zhao,
Y. D. Li,
Yi-feng Yang,
H. F. Yang,
A. J. Liang,
Z. K. Liu,
H. Yao,
Y. P. Qi,
Y. L. Chen,
L. X. Yang
Abstract:
The interaction between localized f and itinerant conduction electrons is crucial in the electronic properties of heavy fermion and valence fluctuating compounds. Using high-resolution angle-resolved photoemission spectroscopy, we systematically investigate the electronic structure of the archetypical valence fluctuating compound EuNi2P2 that hosts multiple f electrons. At low temperatures, we rev…
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The interaction between localized f and itinerant conduction electrons is crucial in the electronic properties of heavy fermion and valence fluctuating compounds. Using high-resolution angle-resolved photoemission spectroscopy, we systematically investigate the electronic structure of the archetypical valence fluctuating compound EuNi2P2 that hosts multiple f electrons. At low temperatures, we reveal the hybridization between Eu 4f and Ni 3d states, which contributes to the electron mass enhancement, consistent with the periodic Anderson model. With increasing temperature, interestingly, we observe opposite temperature evolution of electron spectral function above and below the Kondo coherence temperature near 110 K, which is in contrast to the monotonic valence change and beyond the expectation of the periodic Anderson model. We argue that both f-d hybridization and correlation are imperative in the electronic properties of EuNi2P2. Our results shed light on the understanding of novel properties, such as heavy fermion behaviors and valence fluctuation, of rare-earth transition-metal intermetallic compounds with multiple f electrons.
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Submitted 26 June, 2022;
originally announced June 2022.
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Visualizing bulk and edge photocurrent flow in anisotropic Weyl semimetals
Authors:
Yu-Xuan Wang,
Xin-Yue Zhang,
Chunhua Li,
Xiaohan Yao,
Ruihuan Duan,
Thomas K. M. Graham,
Zheng Liu,
Fazel Tafti,
David Broido,
Ying Ran,
Brian B. Zhou
Abstract:
Materials that rectify light into current in their bulk are desired for optoelectronic applications. In inversion-breaking Weyl semimetals, bulk photocurrents may arise due to nonlinear optical processes that are enhanced near the Weyl nodes. However, the photoresponse of these materials is commonly studied by scanning photocurrent microscopy (SPCM), which convolves the effects of photocurrent gen…
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Materials that rectify light into current in their bulk are desired for optoelectronic applications. In inversion-breaking Weyl semimetals, bulk photocurrents may arise due to nonlinear optical processes that are enhanced near the Weyl nodes. However, the photoresponse of these materials is commonly studied by scanning photocurrent microscopy (SPCM), which convolves the effects of photocurrent generation and collection. Here, we directly image the photocurrent flow inside the type-II Weyl semimetals WTe2 and TaIrTe4 using high-sensitivity quantum magnetometry with nitrogen-vacancy center spins. We elucidate an unknown mechanism for bulk photocurrent generation termed the anisotropic photothermoelectric effect (APTE), where unequal thermopowers along different crystal axes drive intricate circulations of photocurrent around the photoexcitation. Using simultaneous SPCM and magnetic imaging at the sample's interior and edges, we visualize how the APTE stimulates the long-range photocurrent collected in our Weyl semimetal devices through the Shockley-Ramo theorem. Our results highlight an overlooked, but widely relevant source of current flow and inspire novel photodetectors using homogeneous materials with anisotropy.
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Submitted 13 December, 2022; v1 submitted 31 March, 2022;
originally announced March 2022.
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Controlled synthesis of MoxW1-xTe2 atomic layers with emergent quantum states
Authors:
Ya Deng,
Peiling Li,
Chao Zhu,
Jiadong Zhou,
Xiaowei Wang,
Jian Cui,
Xue Yang,
Li Tao,
Qingsheng Zeng,
Ruihuan Duan,
Qundong Fu,
Chao Zhu,
Jianbin Xu,
Fanming Qu,
Changli Yang,
Xiunian Jing,
Li Lu,
Guangtong Liu,
Zheng Liu
Abstract:
Recently, new states of matter like superconducting or topological quantum states were found in transition metal dichalcogenides (TMDs) and manifested themselves in a series of exotic physical behaviors. Such phenomena have been demonstrated to exist in a series of transition metal tellurides including MoTe2, WTe2 and alloyed MoxW1-xTe2. However, the behaviors in the alloy system have been rarely…
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Recently, new states of matter like superconducting or topological quantum states were found in transition metal dichalcogenides (TMDs) and manifested themselves in a series of exotic physical behaviors. Such phenomena have been demonstrated to exist in a series of transition metal tellurides including MoTe2, WTe2 and alloyed MoxW1-xTe2. However, the behaviors in the alloy system have been rarely addressed due to their difficulty in obtaining atomic layers with controlled composition, albeit the alloy offers a great platform to tune the quantum states. Here, we report a facile CVD method to synthesize the MoxW1-xTe2 with controllable thickness and chemical composition ratios. The atomic structure of monolayer MoxW1-xTe2 alloy was experimentally confirmed by scanning transmission electron microscopy (STEM). Importantly, two different transport behaviors including superconducting and Weyl semimetal (WSM) states were observed in Mo-rich Mo0.8W0.2Te2 and W-rich Mo0.2W0.8Te2 samples respectively. Our results show that the electrical properties of MoxW1-xTe2 can be tuned by controlling the chemical composition, demonstrating our controllable CVD growth method is an efficient strategy to manipulate the physical properties of TMDCs. Meanwhile, it provides a perspective on further comprehension and shed light on the design of device with topological multicomponent TMDCs materials.
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Submitted 20 July, 2021;
originally announced July 2021.
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Many-body effect in optical properties of monolayer molybdenum diselenide
Authors:
Ke Xiao,
Tengfei Yan,
Qiye Liu,
Siyuan Yang,
Chiming Kan,
Ruihuan Duan,
Zheng Liu,
Xiaodong Cui
Abstract:
Excitons in monolayer transition metal dichalcogenide (TMD) provide a paradigm of composite Boson in 2D system. This letter reports a photoluminescence and reflectance study of excitons in monolayer molybdenum diselenide (MoSe2) with electrostatic gating. We observe the repulsive and attractive Fermi polaron modes of the band edge exciton, its excited state and the spin-off excitons. Our data vali…
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Excitons in monolayer transition metal dichalcogenide (TMD) provide a paradigm of composite Boson in 2D system. This letter reports a photoluminescence and reflectance study of excitons in monolayer molybdenum diselenide (MoSe2) with electrostatic gating. We observe the repulsive and attractive Fermi polaron modes of the band edge exciton, its excited state and the spin-off excitons. Our data validate the polaronic behavior of excitonic states in the system quantitatively where the simple three-particle trion model is insufficient to explain.
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Submitted 24 August, 2020;
originally announced August 2020.
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Spectroscopic Signature for Local-moment Magnetism in van der Waals Ferromagnet Fe$_3$GeTe$_2$
Authors:
X. Xu,
Y. W. Li,
S. R. Duan,
S. L. Zhang,
Y. J. Chen,
L. Kang,
A. J. Liang,
C. Chen,
W. Xia,
Y. Xu,
P. Malinowski,
X. D. Xu,
J. -H. Chu,
G. Li,
Y. F. Guo,
Z. K. Liu,
L. X. Yang,
Y. L. Chen
Abstract:
The van der Waals ferromagnet Fe$_3$GeTe$_2$ has recently attracted extensive research attention due to its intertwined magnetic, electronic and topological properties. Here, using high-resolution angle-resolved photoemission spectroscopy, we systematically investigate the temperature evolution of the electronic structure of bulk Fe$_3$GeTe$_2$. We observe largely dispersive energy bands that are…
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The van der Waals ferromagnet Fe$_3$GeTe$_2$ has recently attracted extensive research attention due to its intertwined magnetic, electronic and topological properties. Here, using high-resolution angle-resolved photoemission spectroscopy, we systematically investigate the temperature evolution of the electronic structure of bulk Fe$_3$GeTe$_2$. We observe largely dispersive energy bands that are narrowed by a factor of 1.6 compared with ab-initio calculation. Upon heating towards the ferromagnetic transition near 225 K, we observe a massive reduction of quasiparticle coherence in a large energy range, which is attributed to the enhanced magnetic fluctuation in the system. Remarkably, the electron bands barely shift with increasing temperature, which deviates from the exchange splitting picture within the itinerant Stoner model. We argue that the local magnetic moments play a crucial role in the ferromagnetism of Fe$_3$GeTe$_2$, despite its strongly itinerant nature. Our results provide important insights into the electronic and magnetic properties of Fe$_3$GeTe$_2$ and shed light on the generic understanding of itinerant magnetism in correlated materials.
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Submitted 21 April, 2020;
originally announced April 2020.