鈷基蜂窩狀磁體 BaCo2(AsO4)2 中的磁連續體The authors present time-domain terahertz spectroscopy measurements on BaCo2(AsO4)2, a promising 3d transition-metal-based quantum spin liquid candidate.
A magnetic continuum in the cobalt-based honeycomb magnet BaCo2(AsO4)2Quantum spin liquids (QSLs) are topologically ordered states of matter that host fractionalized excitations. A particular route towards a QSL is via strongly bond-dependent interactions on the hexagonal lattice. A number of Ru- and Ir-based candidate Kitaev QSL materials have been pursued, but all have appreciable non-Kitaev interactions. Using time-domain terahertz spectroscopy, we observed a broad magnetic continuum over a wide range of temperatures and fields in the honeycomb cobalt-based magnet BaCo2(AsO4)2, which has been proposed to be a more ideal version of a Kitaev QSL. Applying an in-plane magnetic field of ~0.5 T suppresses the magnetic order, and at higher fields, applying the field gives rise to a spin-polarized state. Under a 4 T magnetic field that was oriented principally out of plane, a broad magnetic continuum was observed that may be consistent with a field-induced QSL. Our results indicate BaCo2(AsO4)2 is a promising QSL candidate.The broad magnetic continuum investigated by time-domain terahertz spectroscopy.Xinshu Zhang, Yuanyuan Xu, T. Halloran, Ruidan Zhong, C. Broholm, R. J. Cava, N. Drichko & N. P. Armitage
doi:10.1038/s41563-022-01403-1
To realize electronic operations beyond the von Neumann bottleneck, a new type of switch that can mimic self-learning is needed. Here, the authors demonstrate all-in-one-place logic and memory operations based on dynamic molecular switch that can emulate brain-like synaptic and Pavlovian response, bringing the field a step closer to molecular-scale hardware.
Dynamic molecular switches with hysteretic negative differential conductance emulating synaptic behaviourTo realize molecular-scale electrical operations beyond the von Neumann bottleneck, new types of multifunctional switches are needed that mimic self-learning or neuromorphic computing by dynamically toggling between multiple operations that depend on their past. Here, we report a molecule that switches from high to low conductance states with massive negative memristive behaviour that depends on the drive speed and number of past switching events, with all the measurements fully modelled using atomistic and analytical models. This dynamic molecular switch emulates synaptic behavior and Pavlovian learning, all within a 2.4-nm-thick layer that is three orders of magnitude thinner than a neuronal synapse. The dynamic molecular switch provides all the fundamental logic gates necessary for deep learning because of its time-domain and voltage-dependent plasticity. The synapse-mimicking multifunctional dynamic molecular switch represents an adaptable molecular-scale hardware operable in solid-state devices, and opens a pathway to simplify dynamic complex electrical operations encoded within a single ultracompact component.The dynamic molecular junction.Yulong Wang, Qian Zhang, Hippolyte P. A. G. Astier, Cameron Nickle, Saurabh Soni, Fuad A. Alami, Alessandro Borrini, Ziyu Zhang, Christian Honnigfort, Björn Braunschweig, Andrea Leoncini, Dong-Cheng Qi, Yingmei Han, Enrique del Barco, Damien Thompson & Christian A. Nijhuis
doi:10.1038/s41563-022-01402-2
單層α-RuCl3中結構對稱性破缺驅動的磁各向異性反轉The authors report a crossover from easy-plane to easy-axis magnetic anisotropy in monolayer RuCl3, which they attribute to an in-plane distortion of the Cl atoms observed in electron diffraction that modify the non-Kitaev exchange terms. The results are useful for overcoming the challenge of realizing a quantum spin liquid.
Magnetic anisotropy reversal driven by structural symmetry-breaking in monolayer α-RuCl3Layered α-RuCl3 is a promising material to potentially realize the long-sought Kitaev quantum spin liquid with fractionalized excitations. While evidence of this state has been reported under a modest in-plane magnetic field, such behaviour is largely inconsistent with theoretical expectations of spin liquid phases emerging only in out-of-plane fields. These predicted field-induced states have been largely out of reach due to the strong easy-plane anisotropy of bulk crystals, however. We use a combination of tunnelling spectroscopy, magnetotransport, electron diffraction and ab initio calculations to study the layer-dependent magnons, magnetic anisotropy, structure and exchange coupling in atomically thin samples. Due to picoscale distortions, the sign of the average off-diagonal exchange changes in monolayer α-RuCl3, leading to a reversal of spin anisotropy to easy-axis anisotropy, while the Kitaev interaction is concomitantly enhanced. Our work opens the door to the possible exploration of Kitaev physics in the true two-dimensional limit.Three-dimensional electron diffraction and demonstration of IETS measurements on 1L α-RuCl3.
Bowen Yang, Yin Min Goh, Suk Hyun Sung, Gaihua Ye, Sananda Biswas, David A. S. Kaib, Ramesh Dhakal, Shaohua Yan, Chenghe Li, Shengwei Jiang, Fangchu Chen, Hechang Lei, Rui He, Roser Valentí, Stephen M. Winter, Robert Hovden & Adam W. Tsen
doi:10.1038/s41563-022-01401-3
Kitaev磁體α-RuCl3中拓撲玻色子的平面熱霍爾效應The authors report a strongly temperature-dependent thermal conductivity at low temperature, consistent with topological bosonic modes in a Chern-insulator-like model.
Planar thermal Hall effect of topological bosons in the Kitaev magnet α-RuCl3The honeycomb magnet α-RuCl3 has attracted considerable interest because it is proximate to the Kitaev Hamiltonian whose excitations are Majoranas and vortices. The thermal Hall conductivity κxy of Majorana fermions is predicted to be half-quantized. Half-quantization of κxy/T (T, temperature) was recently reported, but this observation has proven difficult to reproduce. Here, we report detailed measurements of κxy on α-RuCl3 with the magnetic field B ∥ a (zigzag axis). In our experiment, κxy/T is observed to be strongly temperature dependent between 0.5 and 10 K. We show that its temperature profile matches the distinct form expected for topological bosonic modes in a Chern-insulator-like model. Our analysis yields magnon band energies in agreement with spectroscopic experiments. At high B, the spin excitations evolve into magnon-like modes with a Chern number of ~1. The bosonic character is incompatible with half-quantization of κxy/T.Planar thermal Hall response of α-RuCl3 with B ∥ a.
Peter Czajka, Tong Gao, Max Hirschberger, Paula Lampen-Kelley, Arnab Banerjee, Nicholas Quirk, David G. Mandrus, Stephen E. Nagler & N. P. Ong
doi:10.1038/s41563-022-01397-w
間隙摻雜微量多價陽離子抑制金屬鹵化物鈣鈦礦中的離子遷移Ion migration has a detrimental effect on the performance and stability of halide perovskite optoelectronics. Here, the authors incorporated a small dosage of high-valence neodymium cation to suppress this, with a minimal impact on the lattice microstrain.
Suppressing ion migration in metal halide perovskite via interstitial doping with a trace amount of multivalent cationsCations with suitable sizes to occupy an interstitial site of perovskite crystals have been widely used to inhibit ion migration and promote the performance and stability of perovskite optoelectronics. However, such interstitial doping inevitably leads to lattice microstrain that impairs the long-range ordering and stability of the crystals, causing a sacrificial trade-off. Here, we unravel the evident influence of the valence states of the interstitial cations on their efficacy to suppress the ion migration. Incorporation of a trivalent neodymium cation (Nd3+) effectively mitigates the ion migration in the perovskite lattice with a reduced dosage (0.08%) compared to a widely used monovalent cation dopant (Na+, 0.45%). The photovoltaic performances and operational stability of the prototypical perovskite solar cells are enhanced with a trace amount of Nd3+ doping while minimizing the sacrificial trade-off.Theoretical models of iodide ion migration pathway and detrimental effects of induced tensile microstrain.
Yepin Zhao, Ilhan Yavuz, Minhuan Wang, Marc H. Weber, Mingjie Xu, Joo-Hong Lee, Shaun Tan, Tianyi Huang, Dong Meng, Rui Wang, Jingjing Xue, Sung-Joon Lee, Sang-Hoon Bae, Anni Zhang, Seung-Gu Choi, Yanfeng Yin, Jin Liu, Tae-Hee Han, Yantao Shi, Hongru Ma, Wenxin Yang, Qiyu Xing, Yifan Zhou, Pengju Shi, Sisi Wang, Elizabeth Zhang, Jiming Bian, Xiaoqing Pan, Nam-Gyu Park, Jin-Wook Lee & Yang Yang
doi:10.1038/s41563-022-01390-3
四維跟蹤電荷載流子揭示多晶鹵化物鈣鈦礦中有效的垂直電荷傳輸A discrepancy exists between the low diffusion coefficients and near-unity charge collection efficiencies achieved in practical halide perovskite solar cells. Here, the authors explain this through the discovery of strong heterogeneity in vertical charge diffusivities in a 3D perovskite film.
Efficient vertical charge transport in polycrystalline halide perovskites revealed by four-dimensional tracking of charge carriersFast diffusion of charge carriers is crucial for efficient charge collection in perovskite solar cells. While lateral transient photoluminescence microscopies have been popularly used to characterize charge diffusion in perovskites, there exists a discrepancy between low diffusion coefficients measured and near-unity charge collection efficiencies achieved in practical solar cells. Here, we reveal hidden microscopic dynamics in halide perovskites through four-dimensional (directions x, y and z and time t) tracking of charge carriers by characterizing out-of-plane diffusion of charge carriers. By combining this approach with confocal microscopy, we discover a strong local heterogeneity of vertical charge diffusivities in a three-dimensional perovskite film, arising from the difference between intragrain and intergrain diffusion. We visualize that most charge carriers are efficiently transported through the direct intragrain pathways or via indirect detours through nearby areas with fast diffusion. The observed anisotropy and heterogeneity of charge carrier diffusion in perovskites rationalize their high performance as shown in real devices. Our work also foresees that further control of polycrystal growth will enable solar cells with micrometres-thick perovskites to achieve both long optical path length and efficient charge collection simultaneously.Characterization of the out-of-plane charge diffusion across the FAPbI3 perovskite film.Changsoon Cho, Sascha Feldmann, Kyung Mun Yeom, Yeoun-Woo Jang, Simon Kahmann, Jun-Yu Huang, Terry Chien‐Jen Yang, Mohammed Nabaz Taher Khayyat, Yuh-Renn Wu, Mansoo Choi, Jun Hong Noh, Samuel D. Stranks & Neil C. Greenham
doi:10.1038/s41563-022-01395-y
基於單層 MoS2 光電晶體管陣列的有源像素傳感器矩陣Low-power and compact active pixel sensor (APS) matrices are desired for resource-limited edge devices. Here, the authors report a small-footprint APS matrix based on monolayer MoS2 phototransistors arrays exhibiting spectral uniformity, reconfigurable photoresponsivity and de-noising capabilities at low energy consumption.
Active pixel sensor matrix based on monolayer MoS2 phototransistor arrayIn-sensor processing, which can reduce the energy and hardware burden for many machine vision applications, is currently lacking in state-of-the-art active pixel sensor (APS) technology. Photosensitive and semiconducting two-dimensional (2D) materials can bridge this technology gap by integrating image capture (sense) and image processing (compute) capabilities in a single device. Here, we introduce a 2D APS technology based on a monolayer MoS2 phototransistor array, where each pixel uses a single programmable phototransistor, leading to a substantial reduction in footprint (900 pixels in ∼0.09 cm2) and energy consumption (100s of fJ per pixel). By exploiting gate-tunable persistent photoconductivity, we achieve a responsivity of ∼3.6 × 10^7 A W−1, specific detectivity of ∼5.6 × 10^13 Jones, spectral uniformity, a high dynamic range of ∼80 dB and in-sensor de-noising capabilities. Further, we demonstrate near-ideal yield and uniformity in photoresponse across the 2D APS array.
Akhil Dodda, Darsith Jayachandran, Andrew Pannone, Nicholas Trainor, Sergei P. Stepanoff, Megan A. Steves, Shiva Subbulakshmi Radhakrishnan, Saiphaneendra Bachu, Claudio W. Ordonez, Jeffrey R. Shallenberger, Joan M. Redwing, Kenneth L. Knappenberger, Douglas E. Wolfe & Saptarshi Das
doi:10.1038/s41563-022-01398-9
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