Showing 1–50 of 221 results for author: Cui, Y

Channel-last gate-all-around nanosheet oxide semiconductor transistors

Authors: Fabia F. Athena, Xiangjin Wu, Nathaniel S. Safron, Amy Siobhan McKeown-Green, Mauro Dossena, Jack C. Evans, Jonathan Hartanto, Yukio Cho, Donglai Zhong, Tara Peña, Paweł Czaja, Parivash Moradifar, Paul C. McIntyre, Mathieu Luisier, Yi Cui, Jennifer A. Dionne, Greg Pitner, Iuliana P. Radu, Eric Pop, Alberto Salleo, H. -S. Philip Wong

Abstract: As we move beyond the era of transistor miniaturization, back-end-of-line-compatible transistors that can be stacked monolithically in the third dimension promise improved performance for low-power electronics. In advanced transistor architectures, such as gate-all-around nanosheets, the conventional channel-first process involves depositing dielectrics directly onto the channel. Atomic layer depo… ▽ More As we move beyond the era of transistor miniaturization, back-end-of-line-compatible transistors that can be stacked monolithically in the third dimension promise improved performance for low-power electronics. In advanced transistor architectures, such as gate-all-around nanosheets, the conventional channel-first process involves depositing dielectrics directly onto the channel. Atomic layer deposition of gate dielectrics on back-end-of-line compatible channel materials, such as amorphous oxide semiconductors, can induce defects or cause structural modifications that degrade electrical performance. While post-deposition annealing can partially repair this damage, it often degrades other device metrics. We report a novel channel-last concept that prevents such damage. Channel-last gate-all-around self-aligned transistors with amorphous oxide-semiconductor channels exhibit high on-state current ($>$ 1 mA/$μ$m) and low subthreshold swing (minimum of 63 mV/dec) without the need for post-deposition processing. This approach offers a general, scalable pathway for transistors with atomic layer deposited channel materials, enabling the future of low-power three-dimensional electronics. △ Less

Submitted 24 December, 2025; originally announced December 2025.

Single-crystal growth, structural characterization, and physical properties of a decorated square-kagome antiferromagnet KCu$_7$TeO$_4$(SO$_4$)$_5$Cl

Authors: Jingjing Jing, Andreas Eich, Yiqiu Liu, Lunhua He, Aifeng Wang, Yisheng Chai, Young Sun, Yi Cui, Weiqiang Yu, Xinrun Mi, Michael Merz, Mingquan He

Abstract: The square-kagome lattice, composed of two-dimensional corner-sharing triangles, provides a novel platform for studying frustrated magnetism. However, material realizations of the square-kagome lattice remain scarce. Here, we report the single-crystal growth, structural characterization, magnetic and electric properties of KCu$_7$TeO$_4$(SO$_4$)$_5$Cl, a nabokoite-type compound featuring a distort… ▽ More The square-kagome lattice, composed of two-dimensional corner-sharing triangles, provides a novel platform for studying frustrated magnetism. However, material realizations of the square-kagome lattice remain scarce. Here, we report the single-crystal growth, structural characterization, magnetic and electric properties of KCu$_7$TeO$_4$(SO$_4$)$_5$Cl, a nabokoite-type compound featuring a distorted and decorated square-kagome lattice. Weak anomalies near 4 K are observed in both magnetization and specific heat, indicating the onset of a magnetic transition.The formation of a long-range antiferromagnetic state below 4.5 K is further confirmed by $^{35}$Cl nuclear magnetic resonance (NMR) measurements. Magnetic susceptibility data reveal nearly isotropic Curie-Weiss temperatures ($\sim-145$ K) and $g$-factors ($\sim2.4$) for both in-plane and out-of-plane magnetic fields. Moreover, we observe two successive ferroelectric transitions at $T_\mathrm{FE1}\sim30$ K and $T_\mathrm{FE2}\sim27$ K, driven by inversion-symmetry breaking, most likely associated with distortions in the Cu2O$_4$Cl$_1$ pyramids and the adjacent SO$_4$ tetrahedra. These results suggest that a three-dimensional model incorporating interlayer couplings via decorating sites is essential for capturing the magnetic and electric behaviors in KCu$_7$TeO$_4$(SO$_4$)$_5$Cl. △ Less

Submitted 10 December, 2025; originally announced December 2025.

Comments: 11 pages, 5 figures

Defect Engineered Hexagonal-Boron Nitride Enables Ionic Conduction for Lithium Metal Batteries

Authors: Yecun Wu, Yan-Kai Tzeng, Hao Chen, Kun Xu, Gangbin Yan, Takashi Taniguchi, Kenji Watanabe, Arun Majumdar, Yi Cui, Steven Chu

Abstract: The practical implementation of lithium-metal anodes has been hindered by uncontrollable dendrite formation and interfacial instability. This study presents a defect-engineering approach of a chemically stable and electrically insulating interfacial layer of hexagonal boron nitride (h-BN) that markedly enhances ionic conductivity through argon ion irradiation. Initially, the electrochemical perfor… ▽ More The practical implementation of lithium-metal anodes has been hindered by uncontrollable dendrite formation and interfacial instability. This study presents a defect-engineering approach of a chemically stable and electrically insulating interfacial layer of hexagonal boron nitride (h-BN) that markedly enhances ionic conductivity through argon ion irradiation. Initially, the electrochemical performance from commercially available, large-area chemical vapor deposition (CVD)-grown h-BN films with industrial-scale argon ion implantation motivated our subsequent detailed investigations using lab-scale exfoliated single-crystal h-BN flakes. Integration of these exfoliated flakes into a hybrid microfluidic-microelectronic chip provided direct evidence that controlled vacancy defects transform h-BN into an efficient lithium-ion conductor while preserving its intrinsic electrical insulation. Experimental validation confirmed improved lithium-metal anode stability, achieving dendrite-free cycling with Li plating/stripping Coulombic efficiencies exceeding 99.5% about 1000 cycles. Further assemble of irradiated h-BN in lithium-sulfur batteries effectively mitigates the polysulfide shuttle effect, sustaining over 97% specific capacity around 300 cycles. These results establish a robust, scalable interface-engineering route for next-generation lithium-metal batteries that combine high ionic transport with excellent electrical insulation. △ Less

Submitted 30 October, 2025; originally announced October 2025.

Domain wall induced topological Hall effect in the chiral-lattice ferromagnet Fe$_x$TaS$_2$

Authors: Sk Jamaluddin, Warit Nisaiyok, Yu Zhang, Hari Bhandari, Brian A. Francisco, Peter E. Siegfried, Fehmi Sami Yasin, Tianyi Wang, Abhijeet Nayak, Mohamed El Gazzah, Resham Babu Regmi, June Ho Yeo, Liuyan Zhao, J. F. Mitchell, Yong-Tao Cui, Nirmal J. Ghimire

Abstract: Magnetic topology and its associated emergent phenomena are central to realizing intriguing quantum states and spintronics functionalities. Designing spin textures to achieve strong and distinct electrical responses remains a significant challenge. Layered transition metal dichalcogenides offer a versatile platform for tailoring structural and magnetic properties, enabling access to a wide spectru… ▽ More Magnetic topology and its associated emergent phenomena are central to realizing intriguing quantum states and spintronics functionalities. Designing spin textures to achieve strong and distinct electrical responses remains a significant challenge. Layered transition metal dichalcogenides offer a versatile platform for tailoring structural and magnetic properties, enabling access to a wide spectrum of topological magnetic states. Here, we report a domain-wall-driven, large, and tunable topological Hall effect (THE) in a non-centrosymmetric intercalated transition metal dichalcogenides series Fe$_x$TaS$_2$. By systematically varying the Fe intercalation level, we exert precise control over the magnetic ground states, allowing manipulation of the topological Hall effect. Real-space magnetic force microscopy (MFM) provides direct evidence of periodic magnetic stripe domain formation, confirming the microscopic origin of the observed topological transport phenomena. Our findings establish a promising way for tuning the topology of domains to generate substantial electromagnetic responses in layered magnetic materials. △ Less

Submitted 23 October, 2025; originally announced October 2025.

Scale-bridging dislocation plasticity in MgO at room temperature

Authors: Jiawen Zhang, Zhangtao Li, Yuwei Zhang, Hendrik Holz, James P. Best, Oliver Preuß, Zhenyong Chen, Yinan Cui, Xufei Fang, Wenjun Lu

Abstract: Dislocations in ceramics have recently gained renewed research interest, in contrast to the traditional belief that ceramics are inherently brittle. Understanding dislocation mechanics in representative oxides is beneficial for effective dislocation engineering. Here, we use MgO single crystals with mechanically seeded dislocation densities from about 10 to the power of 12 to about 10 to the power… ▽ More Dislocations in ceramics have recently gained renewed research interest, in contrast to the traditional belief that ceramics are inherently brittle. Understanding dislocation mechanics in representative oxides is beneficial for effective dislocation engineering. Here, we use MgO single crystals with mechanically seeded dislocation densities from about 10 to the power of 12 to about 10 to the power of 15 per square meter to investigate the mechanical behavior such as yield and fracture. Micro-pillar compression tests reveal a dislocation density dependent yield strength, mediated by the varying dominating dislocation mechanisms from nucleation to multiplication/motion. In situ TEM compression measurements highlight the dislocation-seeded samples can achieve a much-improved compressive plastic strain beyond about 70%, with a high yield strength of about 2.35 GPa (diameter of about 400 nm), indicating size effect. Complementary bulk compression tests, along with digital image correlation (DIC), demonstrate a consistent dislocation-mediated deformation and a notable size effect, with bulk samples exhibiting much reduced yield strength (about 120 MPa) compared to the nano-/micro-pillars. Using three-dimensional Discrete Dislocation Dynamics (3D-DDD) simulation, we further qualitatively analyze the collective dislocation activities (slip events) and work hardening during compression. This study provides new insights into dislocation-mediated plasticity in MgO, across different length scales, by systematically tuning dislocation density. △ Less

Submitted 4 November, 2025; v1 submitted 21 October, 2025; originally announced October 2025.

Journal ref: International Journal of Plasticity, 2026

All-Electrical Self-Switching of van der Waals Chiral Antiferromagnet

Authors: Junlin Xiong, Jiawei Jiang, Yanwei Cui, Han Gao, Ji Zhou, Zijia Liu, KuiKui Zhang, Shaobo Cheng, Kehui Wu, Sang-Wook Cheong, Kai Chang, Zhongkai Liu, Hongxin Yang, Shi-Jun Liang, Bin Cheng, Feng Miao

Abstract: Antiferromagnets have garnered significant attention due to their negligible stray field and ultrafast magnetic dynamics, which are promising for high-density and ultrafast spintronic applications. Their dual functionality as both spin sources and information carriers could enable all-electrical self-induced switching of antiferromagnetic order, offering great potential for ultra-compact spintroni… ▽ More Antiferromagnets have garnered significant attention due to their negligible stray field and ultrafast magnetic dynamics, which are promising for high-density and ultrafast spintronic applications. Their dual functionality as both spin sources and information carriers could enable all-electrical self-induced switching of antiferromagnetic order, offering great potential for ultra-compact spintronic devices. However, related progress is still elusive. Here, we report the deterministic switching of chiral antiferromagnetic orders induced by charge current at zero external magnetic field in the van der Waals (vdW) magnetically intercalated transition metal dichalcogenide CoTa3S6. This system exhibits strong interactions between cobalt atom magnetic moment lattice and itinerant electrons within the metallic layers, as demonstrated by temperature-dependent angle-resolved photoemission, scanning tunneling spectroscopy, and topological Nernst effect measurements. Notably, the itinerant-localization interactions lead to current-induced chiral spin orbit torques as well as Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange torques that interact with the localized magnetic moments, facilitating all-electrical switching of the chiral magnetic order in the CoTa3S6 flake. Our work opens a promising avenue for manipulating antiferromagnetic orders by delicately engineering the synergistic interactions between magnetic moments and itinerant electrons. △ Less

Submitted 20 October, 2025; originally announced October 2025.

Epitaxial Electrodeposition of Fe with Controlled In-Plane Variants for Reversible Metal Anode in Aqueous Electrolyte

Authors: Chenxi Sui, Ching-Tai Fu, Guangxia Feng, Yuqi Li, Junyan Li, Gangbin Yan, Po-Chun Hsu, Steven Chu, Yi Cui

Abstract: The development of reversible metal anodes is a key challenge for advancing aqueous battery technologies, particularly for scalable and safe stationary energy storage applications. Here we demonstrate a strategy to realize epitaxial electrodeposition of iron (Fe) on single-crystal copper (Cu) substrates in aqueous electrolytes. We compare the electrodeposition behavior of Fe on polycrystalline and… ▽ More The development of reversible metal anodes is a key challenge for advancing aqueous battery technologies, particularly for scalable and safe stationary energy storage applications. Here we demonstrate a strategy to realize epitaxial electrodeposition of iron (Fe) on single-crystal copper (Cu) substrates in aqueous electrolytes. We compare the electrodeposition behavior of Fe on polycrystalline and single-crystalline Cu substrates, revealing that the latter enables highly uniform, dense, and crystallographically aligned Fe growth. Comprehensive electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) analysis confirms the formation of Fe with specific out-of-plane and in-plane orientations, including well-defined rotational variants. Our findings highlight that epitaxial electrodeposition of Fe can suppress dendritic growth and significantly enhance Coulombic efficiency during plating/stripping cycles. This approach bridges fundamental crystallography with practical electrochemical performance, providing a pathway toward high-efficiency aqueous batteries utilizing Earth-abundant materials. △ Less

Submitted 12 October, 2025; originally announced October 2025.

Spinons, solitons and random singlets in the spin-chain compound copper benzoate

Authors: Ying Chen, Guijing Duan, Yuejiu Zhao, Ning Xi, Bingying Pan, Xiaoyu Xu, Zhanlong Wu, Kefan Du, Shuo Li, Ze Hu, Rui Bian, Xiaoqun Wang, Wei Li, Long Zhang, Yi Cui, Shiyan Li, Rong Yu, Weiqiang Yu

Abstract: The $S=1/2$ antiferromagnetic Heisenberg chain is a paradigmatic quantum system hosting exotic excitations such as spinons and solitons, and forming random singlet state in the presence of quenched disorder. Realizing and distinguishing these excitations in a single material remains a significant challenge. Using nuclear magnetic resonance (NMR) on a high-quality single crystal of copper benzoate,… ▽ More The $S=1/2$ antiferromagnetic Heisenberg chain is a paradigmatic quantum system hosting exotic excitations such as spinons and solitons, and forming random singlet state in the presence of quenched disorder. Realizing and distinguishing these excitations in a single material remains a significant challenge. Using nuclear magnetic resonance (NMR) on a high-quality single crystal of copper benzoate, we identify and characterize all three excitation types by tuning the magnetic field at ultra-low temperatures. At a low field of 0.2 T, a temperature-independent spin-lattice relaxation rate ($1/T_1$) over more than a decade confirms the presence of spinons. Below 0.4 K, an additional relaxation channel emerges, characterized by $1/T_1 \propto T$ and a spectral weight growing as $-\ln(T/T_0)$, signaling a random-singlet ground state induced by weak quenched disorder. At fields above 0.5 T, a field-induced spin gap $Δ\propto H^{2/3}$ observed in both $1/T_1$ and the Knight shift signifies soliton excitations. Our results establish copper benzoate as a unique experimental platform for studying one-dimensional quantum integrability and the interplay of disorder and correlations. △ Less

Submitted 13 October, 2025; originally announced October 2025.

Ultrafast giant enhancement of second harmonic generation in a strongly correlated cobaltite YbBaCo4O7

Authors: Yuchen Cui, Qiaomei Liu, Qiong Wu, Shuxiang Xu, Junhan Huang, Hao Wang, Rongsheng Li, Shanshan Han, Wei Xu, Li Du, Ming Lu, Chunmei Zhang, Shangfei Wu, Xinbo Wang, Tao Dong, Li Yue, Dong Wu, Nanlin Wang

Abstract: We report the observation of ultrafast photoinduced giant enhancement of optical second harmonic generation (SHG) efficiency in cobaltite YbBaCo4O7. Upon femtosecond pumping at energies above the band gap, the system exhibits an ultrafast enhancement in SHG intensity, reaching up to 60% higher than the initial value, then decays into a metastable state maintaining the enhancement. The enhancement… ▽ More We report the observation of ultrafast photoinduced giant enhancement of optical second harmonic generation (SHG) efficiency in cobaltite YbBaCo4O7. Upon femtosecond pumping at energies above the band gap, the system exhibits an ultrafast enhancement in SHG intensity, reaching up to 60% higher than the initial value, then decays into a metastable state maintaining the enhancement. The enhancement scales linearly with pump fluence but shows no dependence on pump polarization. A pure electronic process sets in within the first ~200 fs and is accompanied by a pronounced anisotropic amplification of nonlinear susceptibility. We propose this anomalous SHG enhancement originates from ultrafast electronic band renormalization arising from dynamical modification of multi-electron correlations. In stark contrast to conventional asymmetric systems where SHG is typically suppressed upon photoexcitation, our experimental findings shed a new light on ultrafast optical control nonlinear properties in quantum materials. △ Less

Submitted 3 October, 2025; v1 submitted 2 October, 2025; originally announced October 2025.

Spin-supersolidity induced quantum criticality and magnetocaloric effect in the triangular-lattice antiferromagnet Rb$_2$Co(SeO$_3$)$_2$

Authors: Yi Cui, Zhanlong Wu, Zhongcen Sun, Kefan Du, Jun Luo, Shuo Li, Jie Yang, Jinchen Wang, Rui Zhou, Qian Chen, Yoshimitsu Kohama, Atsuhiko Miyata, Zhuo Yang, Rong Yu, Weiqiang Yu

Abstract: We performed high-field magnetization, magnetocaloric effect (MCE), and NMR measurements on the Ising triangular-lattice antiferromagnet Rb$_2$Co(SeO$_3$)$_2$. The observations of the 1/3-magnetization plateau, the split NMR lines, and the thermal activation behaviors of the spin-lattice relaxation rate $1/T_1$ between 2 T and 15.8 T provide unambiguous evidence of a gapped up-up-down (UUD) magnet… ▽ More We performed high-field magnetization, magnetocaloric effect (MCE), and NMR measurements on the Ising triangular-lattice antiferromagnet Rb$_2$Co(SeO$_3$)$_2$. The observations of the 1/3-magnetization plateau, the split NMR lines, and the thermal activation behaviors of the spin-lattice relaxation rate $1/T_1$ between 2 T and 15.8 T provide unambiguous evidence of a gapped up-up-down (UUD) magnetic ordered phase. For fields between 15.8 T and 18.5 T, the anomaly in the magnetic susceptibility, the slow saturation of the NMR line spectral ratio with temperature, and the power-law temperature dependence of $1/T_1$ suggest the ground state to be a spin supersolid with gapless spin excitations. With further increasing the field, the Grüneisen ratio, extracted from the MCE data, reveals a continuous quantum phase transition at $H_{\rm C}\approx$ 19.5 T and a universal quantum critical scaling with the exponents $νz~\approx~$1. Near $H_{\rm C}$, the large high-temperature MCE signal and the broad peaks in the NMR Knight shift and $1/T_1$, manifest the strong spin fluctuations driven by both magnetic frustration and quantum criticality. These results establish Rb$_2$Co(SeO$_3$)$_2$ as a candidate platform for cryogenic magnetocaloric cooling. △ Less

Submitted 30 September, 2025; originally announced September 2025.

Comments: 7 pages, 5 figures

Spin-polarized chiral ZnIn2S4 for targeted solar-driven CO2 reduction to acetic acid

Authors: Yongping Cui, Yuanbo Li, Zhi-qiang Wang, Xueliang Zhang, Lu Han, Xueli Wang, Jinquan Chen, Aokun Liu, Lu Yu, Changlin Tian, Xue-qing Gong, Wanning Zhang, Yuxi Fang

Abstract: Acetic acid, an important industrial chemical, is a key target product for CO2 reduction due to its dual role in carbon utilization and chemical feedstock supply. Although photocatalytic CO2 reduction (PCCR) can generate acetic acid alongside other multicarbon products, its yield is typically low, limited by competing reactions and inefficient C-C coupling. Herein, we report a chiral mesostructure… ▽ More Acetic acid, an important industrial chemical, is a key target product for CO2 reduction due to its dual role in carbon utilization and chemical feedstock supply. Although photocatalytic CO2 reduction (PCCR) can generate acetic acid alongside other multicarbon products, its yield is typically low, limited by competing reactions and inefficient C-C coupling. Herein, we report a chiral mesostructured ZnIn2S4 (CMZI) photocatalyst that achieves a remarkable acetic acid yield of 962 {umol g-1 h-1 with a high selectivity of 97.3 %. This yield is ten times higher than the current highest reported value, while attaining state-of-the-art selectivity10. The remarkable productivity arises from synergistic effect between chiral structure and sulfur (S) sites of CMZI. Chirality-induced spin polarization in CMZI stabilizes the key triplet OCCO intermediate, significantly promoting C-C coupling efficiency. Theoretical calculations reveal that the S sites on {102} crystal facets of ZnIn2S4 exhibit thermodynamic and kinetic preferences for acetic acid formation. This work offers critical insights into catalytic strategies for CO2 reduction toward the efficient and scalable synthesis of various multicarbon products. △ Less

Submitted 5 October, 2025; v1 submitted 20 September, 2025; originally announced September 2025.

Comments: 9 pages, 4 figures

Isotopically Selected Single Antimony Molecule Doping

Authors: Mason Adshead, Maddison Coke, Evan Tillotson, Kexue Li, Sam Sullivan-Allsop, Ricardo Egoavil, William Thornley, Yi Cui, Christopher M Gourlay, Katie L Moore, Sarah J Haigh, Richard J Curry

Abstract: A reliable route to the deterministic fabrication of impurity ion donors in silicon is required to advance quantum computing architectures based upon such systems. This paper reports the ability to dope isotopically-defined unique (${}^{121}\mathrm{Sb}{}^{123}\mathrm{Sb}$) clusters into silicon with measured detection efficiencies of 94% being obtained. Atomically resolved imaging of the doped clu… ▽ More A reliable route to the deterministic fabrication of impurity ion donors in silicon is required to advance quantum computing architectures based upon such systems. This paper reports the ability to dope isotopically-defined unique (${}^{121}\mathrm{Sb}{}^{123}\mathrm{Sb}$) clusters into silicon with measured detection efficiencies of 94% being obtained. Atomically resolved imaging of the doped clusters reveals a Sb-to-Sb separation of ~2 nm post-implantation, thus indicating suitability to form coupled qudit systems. The method used is fully compatible with integration into processing that includes pre-enrichment of the silicon host to < 3ppm ${}^{29}\mathrm{Si}$ levels. As such, we present a potential pathway to the creation of scaled qudit arrays within silicon platforms for quantum computing. △ Less

Submitted 3 September, 2025; originally announced September 2025.

Comments: 10 pages, 4 figures

Segregation-driven cross-slip mechanism of shockley partials in the gamma prime phase of CoNi-based superalloys

Authors: Zhida Liang, Fengxian Liu, Xin Liu, Yang Li, Yinan Cui, Florian Pyczak

Abstract: In general, the cross-slip of superdislocations (a/2<011>) from {111} planes to {001} planes has been frequently observed in superalloys, accompanied by the formation of an antiphase boundary (APB) and driven by thermal activation. However, no prior studies have evidenced the occurrence of Shockley partial dislocation (a/6<112>) cross-slip within the gamma prime phase of superalloys. In this work,… ▽ More In general, the cross-slip of superdislocations (a/2<011>) from {111} planes to {001} planes has been frequently observed in superalloys, accompanied by the formation of an antiphase boundary (APB) and driven by thermal activation. However, no prior studies have evidenced the occurrence of Shockley partial dislocation (a/6<112>) cross-slip within the gamma prime phase of superalloys. In this work, we present a newly observed cross-slip phenomenon: the Shockley partial dislocations cross-slip from one {111} plane to another {111} conjugate plane, facilitated by the formation of a stair-rod dislocation in the ordered gamma prime phase of a CoNi-based superalloy. Compression tests were conducted at 850 degrees Celsius with a strain rate of 10^-4 s^-1. Defects such as stacking faults and dislocations, along with the associated chemical fluctuations, were characterized using high-resolution scanning transmission electron microscopy (HRSTEM) and energy-dispersive X-ray spectroscopy (EDS). Elemental segregation was found to reduce the activation energy required for cross-slip by decreasing the energies of stacking faults and dislocations. In addition to elemental segregation, local stress concentrations, arising from the combined effects of applied stress, shearing dislocations within the gamma prime phase, and dislocation pile-ups, also play a critical role in triggering cross-slip. The formation of sessile stair-rod dislocations via this newly identified Shockley partial cross-slip in the gamma prime phase is beneficial for enhancing the high-temperature deformation resistance of the alloy by increasing the critical resolved shear stress required for further plastic deformation. △ Less

Submitted 23 August, 2025; originally announced August 2025.

Strong Correlation Driven Quadrupolar to Dipolar Exciton Transitions in a Trilayer Moiré Superlattice

Authors: Yuze Meng, Lei Ma, Li Yan, Ahmed Khalifa, Dongxue Chen, Shuai Zhang, Rounak Banerjee, Takashi Taniguchi, Kenji Watanabe, Seth Ariel Tongay, Benjamin Hunt, Shi-Zeng Lin, Wang Yao, Yong-Tao Cui, Shubhayu Chatterjee, Su-Fei Shi

Abstract: The additional layer degree of freedom in trilayer moiré superlattices of transition metal dichalcogenides enables the emergence of novel excitonic species, such as quadrupolar excitons, which exhibit unique excitonic interactions and hold promise for realizing intriguing excitonic phases and their quantum phase transitions. Concurrently, the presence of strong electronic correlations in moiré sup… ▽ More The additional layer degree of freedom in trilayer moiré superlattices of transition metal dichalcogenides enables the emergence of novel excitonic species, such as quadrupolar excitons, which exhibit unique excitonic interactions and hold promise for realizing intriguing excitonic phases and their quantum phase transitions. Concurrently, the presence of strong electronic correlations in moiré superlattices, as exemplified by the observations of Mott insulators and generalized Wigner crystals, offers a direct route to manipulate these new excitonic states and resulting collective excitonic phases. Here, we demonstrate that strong exciton-exciton and electron-exciton interactions, both stemming from robust electron correlations, can be harnessed to controllably drive transitions between quadrupolar and dipolar excitons. This is achieved by tuning either the exciton density or electrostatic doping in a trilayer semiconducting moiré superlattice. Our findings not only advance the fundamental understanding of quadrupolar excitons but also usher in new avenues for exploring and engineering many-body quantum phenomena through novel correlated excitons in semiconducting moiré systems. △ Less

Submitted 21 August, 2025; originally announced August 2025.

Journal ref: Nature Photonics (2025)

Stable crack propagation in dislocation-engineered oxide visualized by double cleavage drilled compression test

Authors: Oliver Preuß, Zhangtao Li, Enrico Bruder, Philippe Carrez, Yinan Cui, Jürgen Rödel, Xufei Fang

Abstract: Understanding crack tip - dislocation interaction is critical for improving the fracture resistance of semi-brittle materials like room-temperature plastically deformable ceramics. Here, we use a modified double cleavage drilled compression (DCDC) specimen geometry, which facilitates stable crack propagation, to achieve in situ observation of crack tip - dislocation interaction. MgO specimens, fur… ▽ More Understanding crack tip - dislocation interaction is critical for improving the fracture resistance of semi-brittle materials like room-temperature plastically deformable ceramics. Here, we use a modified double cleavage drilled compression (DCDC) specimen geometry, which facilitates stable crack propagation, to achieve in situ observation of crack tip - dislocation interaction. MgO specimens, furnished with dislocation-rich barriers, were employed to study how dislocations influence crack propagation. Crack progression was clearly observed to decelerate within dislocation-rich regions, slowing to 15% of its velocity as compared to the pristine crystal. Upon exiting these regions, cracks reaccelerated until reaching the next dislocation-rich barrier. Coupled phase field and crystal plasticity modeling replicates the experimental observations and provides mechanistic insight into crack tip - dislocation interactions. The aligned experiment and simulation results underscore the robustness of the technique and its potential to inform the design of more fracture-resistant ceramics via dislocations. △ Less

Submitted 16 August, 2025; originally announced August 2025.

Report number: 2025

Journal ref: Journal of the European Ceramic Society, 2025

Realization of a Kondo Insulator in a Multilayer Moire Superlattice

Authors: Qiran Wu, Jingyuan Cui, Ang-Kun Wu, Yuze Meng, Dongxue Chen, Li Yan, Lei Ma, Takashi Taniguchi, Kenji Watanabe, Shi-Zeng Lin, Su-Fei Shi, Yong-Tao Cui

Abstract: Kondo insulators are a paradigmatic strongly correlated electron system, arising from the hybridization between itinerary conduction electrons and localized magnetic moments, which opens a gap in the band of conduction electrons. Traditionally, the known Kondo insulators are found in materials with f-electrons. Recent developments in two-dimensional (2D) moire systems provide a new approach to gen… ▽ More Kondo insulators are a paradigmatic strongly correlated electron system, arising from the hybridization between itinerary conduction electrons and localized magnetic moments, which opens a gap in the band of conduction electrons. Traditionally, the known Kondo insulators are found in materials with f-electrons. Recent developments in two-dimensional (2D) moire systems provide a new approach to generate flat bands with strong electron correlation, which host localized moments at half filling. In this work, we demonstrate the realization of a Kondo insulator phase in a moire superlattice of monolayer WS2 / bilayer WSe2 which hosts a set of moire flat bands in the WSe2 layer interfacing the WS2 layer and dispersive bands in the other WSe2 layer. When both WSe2 layers are partially doped but with a total density of two holes per moire unit cell, an insulating state appears when the density of the moire band is below one hole per moire unit cell. The insulating state disappears above a certain threshold magnetic field and the system becomes metallic, which is a telltale signature of the Kondo insulator. The physics can be well explained by a periodic Anderson lattice model that includes both the on-site Coulomb repulsion in the moire flat band and the hybridization between moire flat and non-moire dispersive bands. Our results suggest that multilayer moire structures of transition metal dichalcogenides provide a tunable platform to simulate the Kondo insulator, which holds promise to tackle many critical open questions in the Kondo insulators. △ Less

Submitted 1 July, 2025; originally announced July 2025.

Dimensionality-Driven Anomalous Metallic State with Zero-field Nonreciprocal Transport in Layered Ising Superconductors

Authors: Yanwei Cui, Zenglin Liu, Qin Liu, Junlin Xiong, Yongqin Xie, Yudi Dai, Ji Zhou, Lizheng Wang, Hanyan Fang, Haiwen Liu, Shi-Jun Liang, Bin Cheng, Feng Miao

Abstract: The anomalous metal state (AMS), observed in failed superconductors, provides insights into superconductivity and quantum criticality, with studies revealing unconventional quantum phases like the Bose metal. Recently, layered transition metal dichalcogenide (TMD) superconductors approaching the two-dimensional limit have garnered significant attention for the enhanced phase fluctuations and elect… ▽ More The anomalous metal state (AMS), observed in failed superconductors, provides insights into superconductivity and quantum criticality, with studies revealing unconventional quantum phases like the Bose metal. Recently, layered transition metal dichalcogenide (TMD) superconductors approaching the two-dimensional limit have garnered significant attention for the enhanced phase fluctuations and electronic correlations. Investigating AMS in these systems, particularly in the absence of an external magnetic field, could offer valuable insights into the dimensionality-driven emergence of exotic quantum phenomena, including triplet Cooper pairing, phase fluctuation dynamics, and especially the recently discovered field-free superconducting diode effects. However, the field-free AMS has yet to be observed in TMD superconductors. Here, we report the dimensionality-tunable AMS near the superconducting quantum phase transitions in a layered TMD superconductor 2H-Ta2S3Se. In samples with thicknesses below 10 nm, we demonstrate magnetic field-driven AMS under external magnetic field, characterized by the vanishing of the Hall resistance and the presence of finite longitudinal resistance. Remarkably, an unexpected zero-field AMS emerges as the sample thickness is reduced to 3 nm. This AMS aligns well with the quantum vortex creep model and exhibits non-reciprocal transport behaviors, suggesting the onset of spontaneous time-reversal symmetry breaking accompanied by vortex motion as the system approaches the two-dimensional limit. Our findings open new avenues for exploring dimensionality-driven exotic superconducting quantum critical phases, and pave the way for a deeper understanding of zero-field superconducting diode effects. △ Less

Submitted 28 May, 2025; originally announced May 2025.

Triplon Bose-Einstein condensation and proximate magnetism in dimerized antiferromagnets

Authors: Z. Y. Zhao, F. Y. Li, C. Dong, R. Chen, M. Y. Cui, Z. W. Ouyang, J. F. Wang, Y. Kohama, Z. Z. He, Gang v. Chen

Abstract: Dimerized quantum magnets provide a useful arena for novel quantum states and phases transitions with the singlet-triplet type of triplon excitations. Here we study the triplon physics and the Bose-Einstein condensation in two isostructural dimerized antiferromagnets $A$Cu(SeO$_3$)$_2$ ($A$ = Hg, Cd). With the systematic measurements, we demonstrate a dimer singlet ground state in HgCu(SeO$_3$)… ▽ More Dimerized quantum magnets provide a useful arena for novel quantum states and phases transitions with the singlet-triplet type of triplon excitations. Here we study the triplon physics and the Bose-Einstein condensation in two isostructural dimerized antiferromagnets $A$Cu(SeO$_3$)$_2$ ($A$ = Hg, Cd). With the systematic measurements, we demonstrate a dimer singlet ground state in HgCu(SeO$_3$)$_2$ with a triplon gap $\sim$ 7.9 K and a triplon Bose-Einstein condensation with an antiferromagnetic order in CdCu(SeO$_3$)$_2$ below 4.4 K. We further adopt the bond-operator technique and show that the elemental replacement preserves the Hamiltonian and allows the study in a unified theoretical framework with tunable interdimer and intradimer interactions on the opposite sides of the quantum critical point. With the peculiar Cu$_2$O$_8$ dimer configuration and effective ferromagnetic interdimer interaction, $A$Cu(SeO$_3$)$_2$ is distinguished from other $S$ = 1/2 dimerized antiferromagnets. Our results represent a global understanding of the magnetic ground states as well as the magnetic transitions in the dimerized magnets of this unusual crystal structure. △ Less

Submitted 26 May, 2025; originally announced May 2025.

Comments: 7 pages, 4 figures, with supplementary materials

Superconductivity and Electron Correlations in Kagome Metal LuOs3B2

Authors: Yusen Xiao, Qingchen Duan, Tao Jia, Yajing Cui, Shaohua Liu, Zhiwei Wen, Liangwen Ji, Ruidan Zhong, Yongliang Chen, Yong Zhao

Abstract: We report a comprehensive investigation of the physical properties of LuOs3B2, characterized by an ideal Os-based kagome lattice. Resistivity and magnetization measurements confirm the emergence of type-II bulk superconductivity with a critical temperature Tc=4.63 K. The specific heat jump and the calculated electron-phonon coupling parameter support a moderately coupled superconducting state. Ele… ▽ More We report a comprehensive investigation of the physical properties of LuOs3B2, characterized by an ideal Os-based kagome lattice. Resistivity and magnetization measurements confirm the emergence of type-II bulk superconductivity with a critical temperature Tc=4.63 K. The specific heat jump and the calculated electron-phonon coupling parameter support a moderately coupled superconducting state. Electron correlation effects are supported by the enhanced Wilson ratios. First-principles calculations reveal hallmark features of kagome band structure, including Dirac points, van Hove singularities, and quasi-flat bands, primarily derived from the Os d orbitals. The inclusion of spin-orbit coupling opens a gap at the Dirac points, significantly altering the electronic properties. Furthermore, the superconductivity and electronic properties of isomorphic compounds are discussed. This work provides a thorough exploration of the superconducting and normal states of LuOs3B2, deepening the understanding of kagome superconductors. △ Less

Submitted 23 April, 2025; originally announced April 2025.

Report number: Phys. Rev. B 111, 195132

Journal ref: Physical Review B 2025

Evidence of Ultrashort Orbital Transport in Heavy Metals Revealed by Terahertz Emission Spectroscopy

Authors: Tongyang Guan, Jiahao Liu, Wentao Qin, Yongwei Cui, Shunjia Wang, Yizheng Wu, Zhensheng Tao

Abstract: The orbital angular momentum of electrons offers a promising, yet largely unexplored, degree of freedom for ultrafast, energy-efficient information processing. As the foundation of orbitronics, understanding how orbital currents propagate and convert into charge currents is essential - but remains elusive due to the challenge in disentangling orbital and spin dynamics in ultrathin films. Although… ▽ More The orbital angular momentum of electrons offers a promising, yet largely unexplored, degree of freedom for ultrafast, energy-efficient information processing. As the foundation of orbitronics, understanding how orbital currents propagate and convert into charge currents is essential - but remains elusive due to the challenge in disentangling orbital and spin dynamics in ultrathin films. Although orbital currents have been predicted to propagate over long distances in materials, recent theoretical studies argue that lattice symmetry may constrain their mean free paths (MFPs) to the scale of a single atomic layer. In this work, we provide the first direct experimental evidence for ultrashort orbital MFPs in heavy metals (HMs) - W, Ta, Pt - revealed by femtosecond terahertz emission spectroscopy. This is enabled by sub-nanometer-precision control of thin-film thickness using wedge-shaped HM|Ni heterostructures. By employing a multi-component terahertz-emission model, we quantitatively extract the orbital MFPs, consistently finding them shorter than their spin counterparts. Furthermore, control experiments rule out interfacial orbital-to-charge conversion as the dominant mechanism, confirming that the process is governed by the bulk inverse orbital Hall effect. Our findings resolve a central controversy in orbitronics and provide key insights into orbital transport and conversion mechanisms. △ Less

Submitted 7 August, 2025; v1 submitted 21 April, 2025; originally announced April 2025.

Deconfined Quantum Critical Point: A Review of Progress

Authors: Yi Cui, Rong Yu, Weiqiang Yu

Abstract: Deconfined quantum critical points (DQCPs) have been proposed as a class of continuous quantum phase transitions occurring between two ordered phases with distinct symmetry-breaking patterns, beyond the conventional framework of Landau-Ginzburg-Wilson (LGW) theory. At the DQCP, the system exhibits emergent gauge fields, fractionalized excitations, and enhanced symmetries. Here we review recent the… ▽ More Deconfined quantum critical points (DQCPs) have been proposed as a class of continuous quantum phase transitions occurring between two ordered phases with distinct symmetry-breaking patterns, beyond the conventional framework of Landau-Ginzburg-Wilson (LGW) theory. At the DQCP, the system exhibits emergent gauge fields, fractionalized excitations, and enhanced symmetries. Here we review recent theoretical and experimental progress on exploring DQCPs in condensed matter systems. We first introduce theoretical advancements in the study of DQCPs over the past twenty years, particularly in magnetic models on square lattices, honeycomb lattices, kagome lattices, and one-dimensional spin chains. We then discuss recent progress on experimental realization of DQCP in quantum magnetic systems. Experimentally, the Shastry-Sutherland model, realized in SrCu$_2$(BO$_3$)$_2$, offers a particularly promising platform for realizing DQCPs. The magnetic frustration inherent to this model drives phase transitions between two distinct symmetry-breaking states: a valence bond solid (VBS) phase and a Néel antiferromagnetic phase. Remarkably, SrCu$_2$(BO$_3$)$_2$ has provided the first experimental evidence of a proximate DQCP through a field-induced Bose-Einstein condensation, transitioning from the VBS state to the Néel state. Nevertheless, the direct experimental realization of a DQCP remains a significant challenge. Despite this, it offers a promising platform for exploring emergent phenomena through quantum phase transition in low-dimensional quantum systems. △ Less

Submitted 14 April, 2025; originally announced April 2025.

Comments: Review article, to appear in Chinese Physics Letters

Journal ref: Chin. Phys. Lett. 42 047503 (2025)

NMR study of supersolid phases in the triangular-lattice antiferromagnet Na2BaCo(PO4)2

Authors: Xiaoyu Xu, Zhanlong Wu, Ying Chen, Qing Huang, Ze Hu, Xinyu Shi, Kefan Du, Shuo Li, Rui Bian, Rong Yu, Yi Cui, Haidong Zhou, Weiqiang Yu

Abstract: We report ultra-low-temperature $^{23}$Na NMR measurements on the Ising triangular lattice antiferromagnet Na$_2$BaCo(PO$_4$)$_2$, which precisely resolve the phase diagram under magnetic field applied along the crystalline $c$ axis. With increasing field, the NMR spectra resolve three ordered phases with distinct spin configurations: the Y, up-up-down (UUD), and V phases. The spin-lattice relaxat… ▽ More We report ultra-low-temperature $^{23}$Na NMR measurements on the Ising triangular lattice antiferromagnet Na$_2$BaCo(PO$_4$)$_2$, which precisely resolve the phase diagram under magnetic field applied along the crystalline $c$ axis. With increasing field, the NMR spectra resolve three ordered phases with distinct spin configurations: the Y, up-up-down (UUD), and V phases. The spin-lattice relaxation rate $1/T_1$ data demonstrate gapless excitations in the Y and V phases, strongly supporting their supersolid nature. However, the phase transitions from the UUD phase to the two supersolid phases exhibit dramatically different behaviors upon cooling. Prior to entering the Y phase, $1/T_1$ identifies a gapless regime within the UUD phase, suggesting a Berezinskii-Kosterlitz-Thouless phase above a second-order phase transition. In contrast, the coexistence of the UUD and V phases observed in our experiments provides direct evidence of a first-order phase transition between these phases. △ Less

Submitted 11 April, 2025; originally announced April 2025.

Comments: 5 pages, 4 figures

Journal ref: Phys. Rev. B 112, 125163 (2025)

Transient Chirality in the Gelation of Adhesive Spinner Monolayers

Authors: Yujie Jiang, Haiquan Li, Yiting Liu, Haoran Li, Yang Cui

Abstract: Active systems of self-rotating elements inherently exhibit chirality, making them of fundamental interest due to parity violation. Using large-scale hydrodynamic simulations, we investigate the gelation of adhesive spinners confined to quasi-2D monolayers at low Reynolds numbers. Unlike the coarsening dynamics of passive colloids, spinner gelation follows a different pathway, displaying structura… ▽ More Active systems of self-rotating elements inherently exhibit chirality, making them of fundamental interest due to parity violation. Using large-scale hydrodynamic simulations, we investigate the gelation of adhesive spinners confined to quasi-2D monolayers at low Reynolds numbers. Unlike the coarsening dynamics of passive colloids, spinner gelation follows a different pathway, displaying structural chirality during the early stages of aggregation. However, this chirality dissipates upon dynamical arrest, resulting in a final gel structure that resembles a conventional colloidal gel. As a result, we find no sign of odd mechanical responses. Nonetheless, the elastic modulus and gelation time remain tunable through spinning activity, providing a new avenue for the bottom-up design of programmable soft materials. △ Less

Submitted 29 April, 2025; v1 submitted 19 March, 2025; originally announced March 2025.

Intrinsic exciton transport and recombination in single-crystal lead bromide perovskite

Authors: Zhixuan Bi, Yunfei Bai, Ying Shi, Tao Sun, Heng Wu, Haochen Zhang, Yuhang Cui, Danlei Zhu, Yubin Wang, Miao-Ling Lin, Yaxian Wang, Dongxin Ma, Ping-Heng Tan, Sheng Meng, Qihua Xiong, Luyi Yang

Abstract: Photogenerated carrier transport and recombination in metal halide perovskites are critical to device performance. Despite considerable efforts, sample quality issues and measurement techniques have limited the access to their intrinsic physics. Here, by utilizing high-purity CsPbBr3 single crystals and contact-free transient grating spectroscopy, we directly monitor exciton diffusive transport fr… ▽ More Photogenerated carrier transport and recombination in metal halide perovskites are critical to device performance. Despite considerable efforts, sample quality issues and measurement techniques have limited the access to their intrinsic physics. Here, by utilizing high-purity CsPbBr3 single crystals and contact-free transient grating spectroscopy, we directly monitor exciton diffusive transport from 26 to 300 K. As the temperature (T) increases, the carrier mobility (μ) decreases rapidly below 100 K wtih a μ~T^{-3.0} scaling, and then follows a more gradual μ~T^{-1.7} trend at higher temperatures. First-principles calculations perfectly reproduce this experimental trend and reveal that optical phonon scattering governs carrier mobility shifts over the entire temperature range, with a single longitudinal optical mode dominating room-temperature transport. Time-resolved photoluminescence further identifies a substantial increase in exciton radiative lifetime with temperature, attributed to increased exciton population in momentum-dark states caused by phonon scattering. Our findings unambiguously resolve previous theory-experiment discrepancies, providing benchmarks for future optoelectronic design. △ Less

Submitted 10 May, 2025; v1 submitted 3 March, 2025; originally announced March 2025.

Journal ref: ACS Nano 19, 19989-20000 (2025)

Effects of particle elongation on dense granular flows down a rough inclined plane

Authors: Jixiong Liu, Lu Jing, Thomas Pähtz, Yifei Cui, Gordon G. D. Zhou, Xudong Fu

Abstract: Granular materials in nature are nearly always non-spherical, but particle shape effects in granular flow remain largely elusive. This study uses discrete element method simulations to investigate how elongated particle shapes affect the mobility of dense granular flows down a rough incline. For a range of systematically varied particle length-to-diameter aspect ratios (AR), we run simulations wit… ▽ More Granular materials in nature are nearly always non-spherical, but particle shape effects in granular flow remain largely elusive. This study uses discrete element method simulations to investigate how elongated particle shapes affect the mobility of dense granular flows down a rough incline. For a range of systematically varied particle length-to-diameter aspect ratios (AR), we run simulations with various flow thicknesses $h$ and slope angles $θ$ to extract the well-known $h_\textrm{stop}(θ)$ curves (below which the flow ceases) and the $Fr$-$h/h_\textrm{stop}$ relations following Pouliquen's approach, where $Fr=u/\sqrt{gh}$ is the Froude number, $u$ is the mean flow velocity, and $g$ is the gravitational acceleration. The slope $β$ of the $Fr$-$h/h_\textrm{stop}$ relations shows an intriguing S-shaped dependence on AR, with two plateaus at small and large AR, respectively, transitioning with a sharp increase. We understand this S-shaped dependence by examining statistics of particle orientation, alignment, and hindered rotation. We find that the rotation ability of weakly elongated particles ($\textrm{AR}\lesssim1.3$) remains similar to spheres, leading to the first plateau in the $β$-AR relation, whereas the effects of particle orientation saturates beyond $\textrm{AR}\approx2.0$, explaining the second plateau. An empirical sigmoidal function is proposed to capture this non-linear dependence. The findings are expected to enhance our understanding of how particle shape affects the flow of granular materials from both the flow- and particle-scale perspectives. △ Less

Submitted 17 January, 2025; originally announced January 2025.

Journal ref: Physical Review E 110 (4), 044902 (2024)

Skin-inspired in-sensor encoding of strain vector using tunable quantum geometry

Authors: Zenglin Liu, Jingwen Shi, Jin Cao, Zecheng Ma, Zaizheng Yang, Yanwei Cui, Lizheng Wang, Yudi Dai, Moyu Chen, Pengfei Wang, Yongqin Xie, Fanqiang Chen, Youguo Shi, Cong Xiao, Shengyuan A. Yang, Bin Cheng, Shi-Jun Liang, Feng Miao

Abstract: Human skin provides crucial tactile feedback, allowing us to skillfully perceive various objects by sensing and encoding complex deformations through multiple parameters in each tactile receptor. However, replicating this high-dimensional tactile perception with conventional materials' electronic properties remains a daunting challenge. Here, we present a skin-inspired method to encode strain vect… ▽ More Human skin provides crucial tactile feedback, allowing us to skillfully perceive various objects by sensing and encoding complex deformations through multiple parameters in each tactile receptor. However, replicating this high-dimensional tactile perception with conventional materials' electronic properties remains a daunting challenge. Here, we present a skin-inspired method to encode strain vectors directly within a sensor. This is achieved by leveraging the strain-tunable quantum properties of electronic bands in the van der Waals topological semimetal Td -WTe2. We observe robust and independent responses from the second-order and third-order nonlinear Hall signals in Td -WTe2 when subjected to variations in both the magnitude and direction of strain. Through rigorous temperature-dependent measurements and scaling law analysis, we establish that these strain responses primarily stem from quantum geometry-related phenomena, including the Berry curvature and Berry-connection polarizability tensor. Furthermore, our study demonstrates that the strain-dependent nonlinear Hall signals can efficiently encode high-dimensional strain information using a single device. This capability enables accurate and comprehensive sensing of complex strain patterns in the embossed character "NJU". Our findings highlight the promising application of topological quantum materials in advancing next-generation, bio-inspired flexible electronics. △ Less

Submitted 7 January, 2025; originally announced January 2025.

Comments: Published in Advanced Functional Materials (2024)

Phase Segregation Dynamics in Mixed-Halide Perovskites Revealed by Plunge-Freeze Cryogenic Electron Microscopy

Authors: Qingyuan Fan, Yi Cui, Yanbin Li, Julian A. Vigil, Zhiqiao Jiang, Partha Nandi, Robert Colby, Chensong Zhang, Yi Cui, Hemamala I. Karunadasa, Aaron M. Lindenberg

Abstract: Mixed-halide lead perovskites, with photoexcited charge-carrier properties suitable for high-efficiency photovoltaics, hold significant promise for high-efficiency tandem solar cells. However, phase segregation under illumination, where an iodide-rich phase forms carrier trap states, remains a barrier to applications. This study employs plunge-freeze cryogenic electron microscopy to visualize nano… ▽ More Mixed-halide lead perovskites, with photoexcited charge-carrier properties suitable for high-efficiency photovoltaics, hold significant promise for high-efficiency tandem solar cells. However, phase segregation under illumination, where an iodide-rich phase forms carrier trap states, remains a barrier to applications. This study employs plunge-freeze cryogenic electron microscopy to visualize nanoscale phase segregation dynamics in CsPb(Br,I) films. By rapidly freezing the illuminated samples, we preserve transient photoexcited ion distributions for high-resolution structural and compositional analysis at the nanoscale. Cryogenic scanning transmission electron microscopy techniques (EELS, 4D-STEM) captured the dynamics of photo-induced iodine migration from grain boundaries to centers, identified the buildup of anisotropic strain, and captured the heterogeneous evolution of this process within a single grain. These findings provide new insights into microscopic phase segregation mechanisms and their dynamics, enhancing our understanding of mixed-halide perovskite photostability. △ Less

Submitted 17 December, 2024; originally announced December 2024.

Comments: 13 pages, 5 figures

Interfacial Perpendicular Magnetic Anisotropy of Ultrathin Fe(001) Film Grown on CoO(001) Surface

Authors: Tong Wu, Yunzhuo Wu, Haoran Chen, Hongyue Xu, Zhen Cheng, Yuanfei Fan, Nan Jiang, Wentao Qin, Yongwei Cui, Yuqiang Gao, Guanhua Zhang, Zhe Yuan, Yizheng Wu

Abstract: Exploring novel systems with perpendicular magnetic anisotropy (PMA) is vital for advancing memory devices. In this study, we report an intriguing PMA system involving an ultrathin Fe layer on an antiferromagnetic (AFM) CoO(001) surface. The measured perpendicular anisotropy field is inversely proportional to the Fe thickness, indicating an interfacial origin of PMA. Temperature-dependent measurem… ▽ More Exploring novel systems with perpendicular magnetic anisotropy (PMA) is vital for advancing memory devices. In this study, we report an intriguing PMA system involving an ultrathin Fe layer on an antiferromagnetic (AFM) CoO(001) surface. The measured perpendicular anisotropy field is inversely proportional to the Fe thickness, indicating an interfacial origin of PMA. Temperature-dependent measurements reveal that the antiferromagnetism of CoO has a negligible effect on the PMA. By leveraging the magneto-optical Kerr effect and birefringence effect, we achieved concurrent visualization of ferromagnetic (FM) and AFM domains. A pronounced coupling effect between these domains was observed near the spin reorientation transition, contrasting sharply with areas of stronger PMA that exhibited weak coupling. This research not only establishes a new FM/AFM bilayer PMA system but also significantly advances the understanding of FM/AFM interfacial interactions. △ Less

Submitted 16 December, 2024; originally announced December 2024.

Comments: 24 pages, 6 figures

Haldane phase, field-induced magnetic ordering and Tomonaga-Luttinger liquid behavior in a spin-one chain compound NiC$_2$O$_4$$\cdot$2NH$_3$

Authors: Shuo Li, Zhanlong Wu, Yanhong Wang, Jun Luo, Kefan Du, Xiaoyu Xu, Ze Hu, Ying Chen, Jie Yang, Zhengxin Liu, Rong Yu, Yi Cui, Rui Zhou, Hongcheng Lu, Weiqiang Yu

Abstract: We performed single-crystal magnetic susceptibility and $^1$H NMR measurements on a quasi-1D, spin-1 antiferromagnet NiC$_2$O$_4$$\cdot$2NH$_3$, with temperature down to 100 mK and with field up to 26 T. With field applied along the chain direction (crystalline $b$ direction), a spin gap is determined at low fields. Our susceptibility and spin-lattice relaxation measurements reveal a Haldane phase… ▽ More We performed single-crystal magnetic susceptibility and $^1$H NMR measurements on a quasi-1D, spin-1 antiferromagnet NiC$_2$O$_4$$\cdot$2NH$_3$, with temperature down to 100 mK and with field up to 26 T. With field applied along the chain direction (crystalline $b$ direction), a spin gap is determined at low fields. Our susceptibility and spin-lattice relaxation measurements reveal a Haldane phase at low field, with an intrachain exchange coupling $J$ $\approx$ 35 K and an easy-plane single-ion anisotropy of 17 K. A field-induced antiferromagnetic (AFM) ordering emerges at fields of 2.1 T, which sets a three-dimensional (3D) quantum critical point (QCP). The high-temperature spin-lattice relaxation rates $1/T_1$ resolves an onset of Tomonaga-Luttinger liquid behavior at field above $3.5$ T, which characterizes a hidden 1D QCP. △ Less

Submitted 29 November, 2024; originally announced November 2024.

Comments: 9 pages, 8 figures

Journal ref: Phys. Rev. B 111, 195164 (2025)

Magnetic order induced chiral phonons in a ferromagnetic Weyl semimetal

Authors: Mengqian Che, Jinxuan Liang, Yunpeng Cui, Hao Li, Bingru Lu, Wenbo Sang, Xiang Li, Xuebin Dong, Le Zhao, Shuai Zhang, Tao Sun, Wanjun Jiang, Enke Liu, Feng Jin, Tiantian Zhang, Luyi Yang

Abstract: Chiral phonons are vibrational modes in a crystal that possess a well-defined handedness or chirality, typically found in materials that lack inversion symmetry. Here we report the discovery of chiral phonon modes in the kagome ferromagnetic Weyl semimetal Co3Sn2S2, a material that preserves inversion symmetry but breaks time-reversal symmetry. Using helicity-resolved magneto-Raman spectroscopy, w… ▽ More Chiral phonons are vibrational modes in a crystal that possess a well-defined handedness or chirality, typically found in materials that lack inversion symmetry. Here we report the discovery of chiral phonon modes in the kagome ferromagnetic Weyl semimetal Co3Sn2S2, a material that preserves inversion symmetry but breaks time-reversal symmetry. Using helicity-resolved magneto-Raman spectroscopy, we observe the spontaneous splitting of the doubly degenerate in-plane Eg modes into two distinct chiral phonon modes of opposite helicity when the sample is zero-field cooled below the Curie temperature, in the absence of an external magnetic field. As we sweep the out-of-plane magnetic field, this Eg phonon splitting exhibits a well-defined hysteresis loop directly correlated with the material's magnetization. The observed spontaneous splitting reaches up to 1.27 cm-1 at low temperatures, progressively diminishes with increasing temperature, and completely vanishes near the Curie temperature. Our findings highlight the role of the magnetic order in inducing chiral phonons, paving the way for novel methods to manipulate chiral phonons through magnetization and vice versa. Additionally, our work introduces new possibilities for controlling chiral Weyl fermions using chiral phonons. △ Less

Submitted 18 February, 2025; v1 submitted 6 November, 2024; originally announced November 2024.

Journal ref: Physical Review Letters 134, 196906 (2025)

Two Plaquette-Singlet Phases and Emergent SO(5) Deconfined Quantum Criticality in SrCu2(BO3)2

Authors: Yi Cui, Kefan Du, Zhanlong Wu, Shuo Li, Pengtao Yang, Ying Chen, Xiaoyu Xu, Hongyu Chen, Chengchen Li, Juanjuan Liu, Bosen Wang, Wenshan Hong, Shiliang Li, Zhiyuan Xie, Jinguang Cheng, Bruce Normand, Rong Yu, Weiqiang Yu

Abstract: The deconfined quantum critical point (DQCP) has become a central open concept in the physics of quantum matter, and its proposed presence in the Shastry-Sutherland model was followed by the experimental observation of at least a minimal DQC scenario induced by an applied magnetic field in SrCu$_2$(BO$_3$)$_2$. However, the nature of the plaquette-singlet phase in SrCu$_2$(BO$_3$)$_2$ remains unre… ▽ More The deconfined quantum critical point (DQCP) has become a central open concept in the physics of quantum matter, and its proposed presence in the Shastry-Sutherland model was followed by the experimental observation of at least a minimal DQC scenario induced by an applied magnetic field in SrCu$_2$(BO$_3$)$_2$. However, the nature of the plaquette-singlet phase in SrCu$_2$(BO$_3$)$_2$ remains unresolved, and with it the identification of the DQCP symmetry from among several theoretical scenarios. Here we perform detailed high-pressure $^{11}$B NMR studies to reveal the presence of both the full-plaquette (FP) and empty-plaquette (EP) phases in SrCu$_2$(BO$_3$)$_2$, phase-separated at a first-order, pressure-driven transition with a volume-fraction effect. The field-driven transition from the EP to the antiferromagnetic (AFM) phase complements our previous observations of the FP--AFM transition, with both showing deconfined quantum criticality, while the scaling of the spin-lattice relaxation rate near the EP--AFM transition, $1/T_1 \propto T^{0.6}$, suggests a DQCP governed by a different universality class. We discuss possible extensions to the Shastry-Sutherland model that account for these pressure and field effects. The expanded phase space we discover mandates an SO(5) DQCP symmetry, and hence our results take an important step towards a complete understanding of deconfined quantum criticality in SrCu$_2$(BO$_3$)$_2$. △ Less

Submitted 8 June, 2025; v1 submitted 31 October, 2024; originally announced November 2024.

Comments: 7 pages, 5 figures

Spin excitations of the Shastry-Sutherland model -- altermagnetism and deconfined quantum criticality

Authors: Hongyu Chen, Guijing Duan, Changle Liu, Yi Cui, Weiqiang Yu, Z. Y. Xie, Rong Yu

Abstract: Frustrated quantum magnets can host a variety of exotic spin excitations, including fractionalized spin excitations coupled to emergent gauge fields at deconfined quantum critical points (DQCPs) and chiral magnons in altermagnets. Here, we investigate the spin excitation spectra of the highly frustrated $S=1/2$ antiferromagnetic (AFM) Shastry-Sutherland model, focusing on the evolution of low-ener… ▽ More Frustrated quantum magnets can host a variety of exotic spin excitations, including fractionalized spin excitations coupled to emergent gauge fields at deconfined quantum critical points (DQCPs) and chiral magnons in altermagnets. Here, we investigate the spin excitation spectra of the highly frustrated $S=1/2$ antiferromagnetic (AFM) Shastry-Sutherland model, focusing on the evolution of low-energy collective modes from the Néel AFM phase to the plaquette valence bond solid (PVBS). We demonstrate that the AFM state exhibits altermagnetic behavior, characterized by a non-relativistic splitting between two chiral magnon bands. Furthermore, we identify two additional low-energy excitations: a Higgs mode in the longitudinal excitation channel and an $S=0$ excitation with vanishing spectral weight. As the system approaches the AFM-to-PVBS transition, both these modes soften along with the lowest-energy triplet and singlet modes in the PVBS state. The closing gap of the Higgs mode, combined with the nearly degenerate velocities of $S=1$ and $S=0$ excitations, provides spectral evidence that the AFM-to-PVBS transition is proximate to a DQCP with emergent $O(4)$ symmetry. Our results help clarify the spectral signature of a broad class of symmetry enhanced quantum phase transitions including deconfined quantum criticality. △ Less

Submitted 14 October, 2025; v1 submitted 31 October, 2024; originally announced November 2024.

Comments: 13 pages, 11 figures

Colossal magnetoresistance from spin-polarized polarons in an Ising system

Authors: Ying-Fei Li, Emily M. Been, Sudhaman Balguri, Chun-Jing Jia, Mira B. Mahenderu, Zhi-Cheng Wang, Yi Cui, Su-Di Chen, Makoto Hashimoto, Dong-Hui Lu, Brian Moritz, Jan Zaanen, Fazel Tafti, Thomas P. Devereaux, Zhi-Xun Shen

Abstract: Recent experiments suggest a new paradigm towards novel colossal magnetoresistance (CMR) in a family of materials EuM$_2$X$_2$(M=Cd, In, Zn; X=P, As), distinct from the traditional avenues involving Kondo-RKKY crossovers, magnetic phase transitions with structural distortions, or topological phase transitions. Here, we use angle-resolved photoemission spectroscopy (ARPES) and density functional th… ▽ More Recent experiments suggest a new paradigm towards novel colossal magnetoresistance (CMR) in a family of materials EuM$_2$X$_2$(M=Cd, In, Zn; X=P, As), distinct from the traditional avenues involving Kondo-RKKY crossovers, magnetic phase transitions with structural distortions, or topological phase transitions. Here, we use angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations to explore their origin, particularly focusing on EuCd$_2$P$_2$. While the low-energy spectral weight royally tracks that of the resistivity anomaly near the temperature with maximum magnetoresistance (T$_{MR}$) as expected from transport-spectroscopy correspondence, the spectra are completely incoherent and strongly suppressed with no hint of a Landau quasiparticle. Using systematic material and temperature dependence investigation complemented by theory, we attribute this non-quasiparticle caricature to the strong presence of entangled magnetic and lattice interactions, a characteristic enabled by the $p$-$f$ mixing. Given the known presence of ferromagnetic clusters, this naturally points to the origin of CMR being the scattering of spin-polarized polarons at the boundaries of ferromagnetic clusters. These results are not only illuminating to investigate the strong correlations and topology in EuCd$_2$X$_2$ family, but, in a broader view, exemplify how multiple cooperative interactions can give rise to extraordinary behaviors in condensed matter systems. △ Less

Submitted 30 October, 2024; originally announced October 2024.

Journal ref: P.N.A.S 121 (50) e2409846121 (2024)

Anomalously Enhanced Diffusivity of Moiré Excitons via Manipulating the Interplay with Correlated Electrons

Authors: Li Yan, Lei Ma, Yuze Meng, Chengxin Xiao, Bo Chen, Qiran Wu, Jingyuan Cui, Qingrui Cao, Rounak Banerjee, Takashi Taniguchi, Kenji Watanabe, Seth Ariel Tongay, Benjamin Hunt, Yong-Tao Cui, Wang Yao, Su-Fei Shi

Abstract: Semiconducting transitional metal dichalcogenides (TMDCs) moiré superlattice provides an exciting platform for manipulating excitons. The in-situ control of moiré potential confined exciton would usher in unprecedented functions of excitonic devices but remains challenging. Meanwhile, as a dipolar composite boson, interlayer exciton in the type-II aligned TMDC moiré superlattice strongly interacts… ▽ More Semiconducting transitional metal dichalcogenides (TMDCs) moiré superlattice provides an exciting platform for manipulating excitons. The in-situ control of moiré potential confined exciton would usher in unprecedented functions of excitonic devices but remains challenging. Meanwhile, as a dipolar composite boson, interlayer exciton in the type-II aligned TMDC moiré superlattice strongly interacts with fermionic charge carriers. Here, we demonstrate active manipulation of the exciton diffusivity by tuning their interplay with correlated carriers in moiré potentials. At fractional fillings where carriers are known to form generalized Wigner crystals, we observed suppressed diffusivity of exciton. In contrast, in Fermi liquid states where carriers dynamically populate all moiré traps, the repulsive carrier-exciton interaction can effectively reduce the moiré potential confinement seen by the exciton, leading to enhanced diffusivity with the increase of the carrier density. Notably, the exciton diffusivity is enhanced by orders of magnitude near the Mott insulator state, and the enhancement is much more pronounced for the 0-degree than the 60-degree aligned WS2/WSe2 heterobilayer due to the more localized nature of interlayer excitons. Our study inspires further engineering and controlling exotic excitonic states in TMDC moiré superlattices for fascinating quantum phenomena and novel excitonic devices. △ Less

Submitted 15 October, 2024; originally announced October 2024.

Magnetostatic effect on spin dynamics properties in antiferromagnetic Van der Waals material CrSBr

Authors: Hongyue Xu, Nan Jiang, Haoran Chen, Yi Chen, Tong Wu, Yongwei Cui, Yunzhuo Wu, Zhiyuan Sheng, Zeyuan Sun, Jia Xu, Qixi Mi, Shiwei Wu, Weichao Yu, Yizheng Wu

Abstract: Van der Waals (vdW) antiferromagnets are exceptional platforms for exploring the spin dynamics of antiferromagnetic materials owing to their weak interlayer exchange coupling. In this study, we examined the antiferromagnetic resonance spectra of anisotropic Van der Waals antiferromagnet CrSBr. In addition to the ordinary resonance modes, we observed a dipolar spin wave mode when the microwave fiel… ▽ More Van der Waals (vdW) antiferromagnets are exceptional platforms for exploring the spin dynamics of antiferromagnetic materials owing to their weak interlayer exchange coupling. In this study, we examined the antiferromagnetic resonance spectra of anisotropic Van der Waals antiferromagnet CrSBr. In addition to the ordinary resonance modes, we observed a dipolar spin wave mode when the microwave field was oriented perpendicular to the in-plane easy axis of CrSBr. Furthermore, our results uncovered a pronounced dependency of various resonant modes on the orientation of the microwave field, which is pivotal for the accurate determination of exchange coupling constants. Numerical simulations have elucidated this orientation dependence of spin dynamics arises from the magnetostatic effect. This discovery underscores the previously underappreciated significance of dipolar interactions in shaping the dynamical properties of two-dimensional AFM materials, thereby enhancing our understanding of the intrinsic dynamic properties of vdW magnets. △ Less

Submitted 19 September, 2024; originally announced September 2024.

Tailoring 4H-SiC Surface Electronic States by Atomic-Layer Deposition for Ideal Peta-Ohm Resistors

Authors: Yuying Xi, Helios Y. Li, Guohui Li, Qingmei Su, Kaili Mao, Bingshe Xu, Yuying Hao, Nicholas X. Fang, Yanxia Cui

Abstract: High resolution resistors capable of detecting minuscule currents are vital for advanced sensors, but existing off-shelf models struggle with inconsistent resistance under varying voltages. The underlying physics of this issue is rooted in unstable surface charges and intrinsic inhomogeneity of surface potential caused by spontaneous polarization (SP) in commercial semi-insulating silicon carbide… ▽ More High resolution resistors capable of detecting minuscule currents are vital for advanced sensors, but existing off-shelf models struggle with inconsistent resistance under varying voltages. The underlying physics of this issue is rooted in unstable surface charges and intrinsic inhomogeneity of surface potential caused by spontaneous polarization (SP) in commercial semi-insulating silicon carbide (SiC) devices. In this work, we found that coating SiC surfaces with an ultrathin zinc oxide layer immobilizes the dangling surface charges in place and balances the natural electric field of the material, ensuring stable resistance even at extreme voltages up to 1000 V. The resulting SiC resistor maintains a record-high resistance of one peta-ohm (10^15 Ω) with negligible voltage fluctuations, outperforming conventional options. Additionally, these devices can switch states when exposed to light or heat, making them dual-purpose tools for ultra-sensitive measurements and sensors. This breakthrough combines high stability, scalability for mass production, and multifunctionality, opening doors to next-generation precision technologies in fields like quantum sensing and environmental monitoring. △ Less

Submitted 26 August, 2025; v1 submitted 14 July, 2024; originally announced July 2024.

Single-Ion Sensing in Liquid Using Fluorescent h-BN Point Defects

Authors: Yecun Wu, Kun Xu, Hori Pada Sarker, Takashi Taniguchi, Kenji Watanabe, Frank Abild-Pedersen, Arun Majumdar, Yi Cui, Yan-Kai Tzeng, Steven Chu

Abstract: Understanding the chemical state of individual ions in solutions is crucial for advancing knowledge of complex systems. However, sensing systems at the single-ion level in liquid environments remains a significant challenge. A strategy is introduced that leverages the optical emission properties of point defects in hexagonal boron nitride (h-BN) as single ion sensors. The interaction of optically… ▽ More Understanding the chemical state of individual ions in solutions is crucial for advancing knowledge of complex systems. However, sensing systems at the single-ion level in liquid environments remains a significant challenge. A strategy is introduced that leverages the optical emission properties of point defects in hexagonal boron nitride (h-BN) as single ion sensors. The interaction of optically active h-BN defects with ions in solution leads to distinct spectral shifts, enabling precise visualization and analyzing of individual ions. Using Li+ ions in organic electrolytes as a model, spectral shifts exceeding 10 nm were observed upon ion addition. Application of an external electric field further enhanced these shifts to over 40 nm, enabling real-time monitoring of electrical field induced local perturbations of Li+ ions. Through this approach, individual point defects were shown to spectroscopically distinguish ions of varying charges (e.g., Na+, Mg2+, and Al3+) based on their local electrical field, each producing a distinct spectral shift. This platform allows direct sensing of ions and their chemical states in liquid environments, providing insights into subtle interfacial changes at the single-ion level, with measurable spectral shifts detectable at millisecond temporal resolution and at concentrations down to 10 micromolar range. This capability presents potential applications in various fields involving ions in liquids that include battery technology and environmental science. △ Less

Submitted 31 October, 2025; v1 submitted 2 July, 2024; originally announced July 2024.

Low-energy spin dynamics in a Kitaev material Na3Ni2BiO6 investigated by NMR

Authors: Xinyu Shi, Yi Cui, Yanyan Shangguan, Xiaoyu Xu, Zhanlong Wu, Ze Hu, Shuo Li, Kefan Du, Ying Chen, Long Ma, Zhengxin Liu, Jinsheng Wen, Jinshan Zhang, Weiqiang Yu

Abstract: We performed 23Na NMR and magnetization measurements on an S = 1, quasi-2D honeycomb lattice antiferromagnet Na3Ni2BiO6. A large positive Curie-Weiss constant of 22.9 K is observed. The NMR spectra at low fields are consistent with a "zigzag" magnetic order, indicating a large easy-axis anisotropy. With field applied along the c* axis, the NMR spectra confirm the existence of a 1/3-magnetization p… ▽ More We performed 23Na NMR and magnetization measurements on an S = 1, quasi-2D honeycomb lattice antiferromagnet Na3Ni2BiO6. A large positive Curie-Weiss constant of 22.9 K is observed. The NMR spectra at low fields are consistent with a "zigzag" magnetic order, indicating a large easy-axis anisotropy. With field applied along the c* axis, the NMR spectra confirm the existence of a 1/3-magnetization plateau phase between 5.1 T and 7.1 T. The transition from the zigzag order to the 1/3-magnetization plateau phase is also found to be a first-order type. A monotonic decrease of the spin gap is revealed in the 1/3-magnetization plateau phase, which reaches zero at a quantum critical field Hc = 8.35 T before entering the fully polarized phase. These data suggest the existence of exchange frustration in the system along with strong ferromagnetic interactions, hosting the possibility for Kitaev physics. Besides, well below the ordered phase, the 1/T1 at high fields shows either a level off or an enhancement upon cooling below 3 K, which suggests the existence of low-energy fluctuations. △ Less

Submitted 11 April, 2024; originally announced April 2024.

Comments: 7 pages, 7 figures

Journal ref: Chinese Phys. B 33 067601 (2024)

Superionic Fluoride Gate Dielectrics with Low Diffusion Barrier for Advanced Electronics

Authors: Kui Meng, Zeya Li, Peng Chen, Xingyue Ma, Junwei Huang, Jiayi Li, Feng Qin, Caiyu Qiu, Yilin Zhang, Ding Zhang, Yu Deng, Yurong Yang, Genda Gu, Harold Y. Hwang, Qi-Kun Xue, Yi Cui, Hongtao Yuan

Abstract: Exploration of new dielectrics with large capacitive coupling is an essential topic in modern electronics when conventional dielectrics suffer from the leakage issue near breakdown limit. To address this looming challenge, we demonstrate that rare-earth-metal fluorides with extremely-low ion migration barriers can generally exhibit an excellent capacitive coupling over 20 $μ$F cm$^{-2}$ (with an e… ▽ More Exploration of new dielectrics with large capacitive coupling is an essential topic in modern electronics when conventional dielectrics suffer from the leakage issue near breakdown limit. To address this looming challenge, we demonstrate that rare-earth-metal fluorides with extremely-low ion migration barriers can generally exhibit an excellent capacitive coupling over 20 $μ$F cm$^{-2}$ (with an equivalent oxide thickness of ~0.15 nm and a large effective dielectric constant near 30) and great compatibility with scalable device manufacturing processes. Such static dielectric capability of superionic fluorides is exemplified by MoS$_2$ transistors exhibiting high on/off current ratios over 10$^8$, ultralow subthreshold swing of 65 mV dec$^{-1}$, and ultralow leakage current density of ~10$^{-6}$ A cm$^{-2}$. Therefore, the fluoride-gated logic inverters can achieve significantly higher static voltage gain values, surpassing ~167, compared to conventional dielectric. Furthermore, the application of fluoride gating enables the demonstration of NAND, NOR, AND, and OR logic circuits with low static energy consumption. Notably, the superconductor-to-insulator transition at the clean-limit Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ can also be realized through fluoride gating. Our findings highlight fluoride dielectrics as a pioneering platform for advanced electronics applications and for tailoring emergent electronic states in condensed matters. △ Less

Submitted 2 April, 2024; originally announced April 2024.

Comments: 33 pages, 5 figures

Molecular intercalation in the van der Waals antiferromagnets FePS3 and NiPS3

Authors: Cong Li, Ze Hu, Xiaofei Hou, Sheng Xu, Zhanlong Wu, Kefan Du, Shuo Li, Xiaoyu Xu, Ying Chen, Zeyu Wang, Tiancheng Mu, Tian-Long Xia, Yanfeng Guo, B. Normand, Weiqiang Yu, Yi Cui

Abstract: We have performed electrochemical treatment of the van der Waals antiferromagnetic materials FePS$_3$ and NiPS$_3$ with the ionic liquid EMIM-BF$_4$, achieving significant molecular intercalation. Mass analysis of the intercalated compounds, EMIM$_x$-FePS$_3$ and EMIM$_x$-NiPS$_3$, indicated respective intercalation levels, $x$, of approximately 27\% and 37\%, and X-ray diffraction measurements de… ▽ More We have performed electrochemical treatment of the van der Waals antiferromagnetic materials FePS$_3$ and NiPS$_3$ with the ionic liquid EMIM-BF$_4$, achieving significant molecular intercalation. Mass analysis of the intercalated compounds, EMIM$_x$-FePS$_3$ and EMIM$_x$-NiPS$_3$, indicated respective intercalation levels, $x$, of approximately 27\% and 37\%, and X-ray diffraction measurements demonstrated a massive (over 50\%) enhancement of the $c$-axis lattice parameters. To investigate the consequences of these changes for the magnetic properties, we performed magnetic susceptibility and $^{31}$P nuclear magnetic resonance (NMR) studies of both systems. For EMIM$_x$-FePS$_3$, intercalation reduces the magnetic ordering temperature from $T_N = 120$~K to 78~K, and we find a spin gap in the antiferromagnetic phase that drops from 45~K to 30~K. For EMIM$_x$-NiPS$_3$, the ordering temperature is almost unaffected (changing from 148~K to 145~K), but a change towards nearly isotropic spin fluctuations suggests an alteration of the magnetic Hamiltonian. Such relatively modest changes, given that the huge extension of the $c$ axes is expected to cause a very strong suppression any interlayer interactions, point unequivocally to the conclusion that the magnetic properties of both parent compounds are determined solely by two-dimensional (2D), intralayer physics. The changes in transition temperatures and low-temperature spin dynamics in both compounds therefore indicate that intercalation also results in a significant modulation of the intralayer magnetic interactions, which we propose is due to charge doping and localization on the P sites. Our study offers chemical intercalation with ionic liquids as an effective method to control not only the interlayer but also the intralayer interactions in quasi-2D magnetic materials. △ Less

Submitted 3 March, 2024; originally announced March 2024.

Journal ref: Physical Review B 109, 184407(2024)

Semiclassical approach to spin dynamics of a ferromagnetic S=1 chain

Authors: Chengchen Li, Yi Cui, Weiqiang Yu, Rong Yu

Abstract: Motivated by recent experimental progress in the quasi-one-dimensional quantum magnet NiNb$_2$O$_6$, we study the spin dynamics of an S=1 ferromagnetic Heisenberg chain with single-ion anisotropy by using a semiclassical molecular dynamics approach. This system undergoes a quantum phase transition from a ferromagnetic to a paramagnetic state under a transverse magnetic field, and the magnetic resp… ▽ More Motivated by recent experimental progress in the quasi-one-dimensional quantum magnet NiNb$_2$O$_6$, we study the spin dynamics of an S=1 ferromagnetic Heisenberg chain with single-ion anisotropy by using a semiclassical molecular dynamics approach. This system undergoes a quantum phase transition from a ferromagnetic to a paramagnetic state under a transverse magnetic field, and the magnetic responses reflecting this transition is well described by our semiclassical method. We show that at low-temperature the transverse component of the dynamical structure factor depicts clearly the magnon dispersion, and the longitudinal component exhibits two continua associated with single- and two-magnon excitations, respectively. These spin excitation spectra show interesting temperature dependence as effects of magnon interactions.Our findings shed light on experimental detection of spin excitations in a large class of quasi-one-dimensional magnets. △ Less

Submitted 31 July, 2024; v1 submitted 27 February, 2024; originally announced February 2024.

Journal ref: Chinese Phys. B 33 (2024) 067501

NMR evidence of spinon localization in kagome antiferromagnet YCu$_3$(OH)$_6$Br$_2$[Br$_{1-x}$(OH)$_x$]

Authors: Shuo Li, Yi Cui, Zhenyuan Zeng, Yue Wang, Ze Hu, Jie Liu, Cong Li, Xiaoyu Xu, Ying Chen, Zhengxin Liu, Shiliang Li, Weiqiang Yu

Abstract: We performed nuclear magnetic resonance studies on a kagome antiferromagnet YCu$_3$(OH)$_6$Br$_2$[Br$_{1-x}$(OH)$_{x}$]. No significant NMR spectral broadening is found in the Br center peak from 1 K down to 0.05 K, indicating absence of static antiferromagnetic ordering. In contrast to signatures of dominant 2D kagome antiferromagnetic fluctuations at temperature above 30 K, both the Knight shift… ▽ More We performed nuclear magnetic resonance studies on a kagome antiferromagnet YCu$_3$(OH)$_6$Br$_2$[Br$_{1-x}$(OH)$_{x}$]. No significant NMR spectral broadening is found in the Br center peak from 1 K down to 0.05 K, indicating absence of static antiferromagnetic ordering. In contrast to signatures of dominant 2D kagome antiferromagnetic fluctuations at temperature above 30 K, both the Knight shift $K_{\rm{n}}$ and the spin-lattice relaxation rate $1/T_{1}$ increase when the sample is cooled from 30 K to 8 K, which can be attributed to the scattering of spin excitations by strong non-magnetic impurities. Unusually, a hump is observed in $K_{\rm{n}}$ and $1/T_{2}$ close to 2 K (far below the exchange energy), which indicates the existence of excitations with a large density of states close to zero energy. These phenomena are reproduced by a mean-field simulation of Heisenberg model with bond-dependent exchange interactions, where the sign fluctuations in the spinon kinetic terms caused by impurities result in localization of spinons and an almost flat band close to the Fermi energy. △ Less

Submitted 8 February, 2024; originally announced February 2024.

Comments: 9 pages, 7 figures. The supplementary materials can be obtained upon request

Journal ref: Physical Review B 109,104403 (2024)

Field-induced phase transitions and quantum criticality in a honeycomb antiferromagnet Na3Co2SbO6

Authors: Ze Hu, Yue Chen, Yi Cui, Shuo Li, Cong Li, Xiaoyu Xu, Ying Chen, Xintong Li, Yuchen Gu, Rong Yu, Rui Zhou, Yuan Li, Weiqiang Yu

Abstract: We performed 23Na NMR measurements on a single-domain crystal of the Kitaev material Na3Co2SbO6, with magnetic field applied along the crystalline a axis. A positive Curie-Weiss constant is obtained from the NMR Knight shift, which suggests the existence of ferromagnetic exchange couplings. The antiferromagnetic ordering is found to be suppressed at a field of 1.9 T. Inside the ordered phase, our… ▽ More We performed 23Na NMR measurements on a single-domain crystal of the Kitaev material Na3Co2SbO6, with magnetic field applied along the crystalline a axis. A positive Curie-Weiss constant is obtained from the NMR Knight shift, which suggests the existence of ferromagnetic exchange couplings. The antiferromagnetic ordering is found to be suppressed at a field of 1.9 T. Inside the ordered phase, our data reveal two additional phase transitions. At 1.9 T, the spin-lattice relaxation rate 1/23T1 establishes a quantum critical behavior at high temperatures. However, at low temperatures, a gapped behavior is observed at the critical field, which suggests a weakly first-order transition instead and a possible field-induced quantum spin liquid. Our results reveal complex microscopic interactions in the system, which may help to search for possible quantum spin liquids. △ Less

Submitted 22 January, 2024; originally announced January 2024.

Comments: 9 pages, 9 figures

Filled Colloidal Gel Rheology: Strengthening, Stiffening, and Tunability

Authors: Yujie Jiang, Yang Cui, Yankai Li, Zhiwei Liu, Christopher Ness, Ryohei Seto

Abstract: Filler-induced strengthening is ubiquitous in materials science and is particularly well-established in polymeric nanocomposites. Despite having similar constituents, colloidal gels with solid filling exhibit distinct rheology, which is of practical interest to industry (e.g., lithium-ion batteries) yet remains poorly understood. We show, using experiments and simulations, that filling monotonical… ▽ More Filler-induced strengthening is ubiquitous in materials science and is particularly well-established in polymeric nanocomposites. Despite having similar constituents, colloidal gels with solid filling exhibit distinct rheology, which is of practical interest to industry (e.g., lithium-ion batteries) yet remains poorly understood. We show, using experiments and simulations, that filling monotonically enhances the yield stress (i.e., strength) of colloidal gels while the elastic modulus (i.e., stiffness) first increases and then decreases. The latter softening effect results from a frustrated gel matrix at dense filling, evidenced by a growing inter-phase pressure. This structural frustration is, however, not detrimental to yielding resistance. Instead, fillers offer additional mechanical support to the gel backbone via percolating force chains, decreasing the yield strain at the same time. We develop a mechanistic picture of this phenomenology that leads us to a novel `filler-removal protocol,' making individual control over the strength and brittleness of a composite gel possible. △ Less

Submitted 27 April, 2024; v1 submitted 15 November, 2023; originally announced November 2023.

Microstructure evolution and characteristics of laser-clad lightweight refractory NbxMo$_{0.5}$Ti$_{1.5}$Ta$_{0.2}$Cr high-entropy alloy

Authors: C. Y. Cui, H. H. Xu, J. Yang, X. G. Cui

Abstract: Lightweight refractory high-entropy alloy coatings (RHEAcs) of NbxMo$_{0.5}$Ti$_{1.5}$Ta$_{0.2}$Cr (where $x=$ 1, 1.3, 1.5, and 2) were fabricated on the surface of 316L stainless steel using laser cladding (LC) technology. A comprehensive study was conducted to elucidate the effect of Nb content on the microstructure, microhardness and wear resistance of NbxMo$_{0.5}$Ti$_{1.5}$Ta$_{0.2}$Cr RHEAcs… ▽ More Lightweight refractory high-entropy alloy coatings (RHEAcs) of NbxMo$_{0.5}$Ti$_{1.5}$Ta$_{0.2}$Cr (where $x=$ 1, 1.3, 1.5, and 2) were fabricated on the surface of 316L stainless steel using laser cladding (LC) technology. A comprehensive study was conducted to elucidate the effect of Nb content on the microstructure, microhardness and wear resistance of NbxMo$_{0.5}$Ti$_{1.5}$Ta$_{0.2}$Cr RHEAcs before and after annealing at 900 for 10 h. The results show that the grains are gradually refined with the increase of Nb content. The coating consists mainly of a body-centered cubic (BCC) solid solution, C15-Laves phase, and a small amount of hexagonal close-packed (HCP) solid solution containing Ti. The microhardness of RHEAcs is significantly higher compared to the base material. Notably, at Nb1.3, due to the influence of lattice dislocations, the microhardness reaches a peak of 1066.5 HV, which is about 7.11 times higher than that of the base material. On the contrary, at Nb$_2$, the microhardness is at its lowest point, averaging 709.31 HV, but 4.72 times that of the base material. After annealing, an increase in microhardness is observed at all Nb concentrations, up to 31.2% at Nb$_2$. Before annealing, the wear resistance of RHEAcs was slightly better than that of 316L stainless steel at different Nb contents. However, after annealing, the coefficient of friction (COF) and wear rate of the coatings are lower than those of annealed 316L stainless steel, highlighting their excellent wear resistance. It is noteworthy that the loss of wear properties after annealing at Nb1 is at a minimum, obtaining the most balanced wear resistance before and after annealing. The enhanced wear resistance after annealing can be attributed to the presence of ultra-fine grain oxide friction layers, mainly composed of TiO2 and Ta2O5 . The main mode of wear is oxidative wear, with a small amount of wear from abrasive wear. △ Less

Submitted 22 October, 2023; originally announced October 2023.

The rotating excitons in two-dimensional materials: Valley Zeeman effect and chirality

Authors: Yu Cui, Xin-Jun Ma, Jia-Pei Deng, Shao-Juan Li, Ran-Bo Yang, Zhi-Qing Li, Zi-Wu Wang

Abstract: We propose the rotational dynamics of the intralayer and interlayer excitons with their inherent momenta of inertia in the monolayer and bilayer transition metal dichalcogenides, respectively, where the new chirality of exciton is endowed by the rotational angular momentum, namely, the formations of left- and right-handed excitons at the +K and -K valleys, respectively. We find that angular moment… ▽ More We propose the rotational dynamics of the intralayer and interlayer excitons with their inherent momenta of inertia in the monolayer and bilayer transition metal dichalcogenides, respectively, where the new chirality of exciton is endowed by the rotational angular momentum, namely, the formations of left- and right-handed excitons at the +K and -K valleys, respectively. We find that angular momenta exchange between excitons and its surrounding phononic bath result in the large fluctuation of the effective g-factor and the asymmetry of valley Zeeman splitting observed in most recently experiments, both of which sensitively depend on the magnetic moments provided by the phononic environment. This rotating exciton model not only proposes a new controllable knob in valleytronics, but opens the door to explore the angular momentum exchange of the chiral quasiparticles with the many-body environment. △ Less

Submitted 8 October, 2023; originally announced October 2023.

Comments: 8 pages, 3 figures. Welcome your comments

Exciton Superposition across Moiré States in a Semiconducting Moiré Superlattice

Authors: Zhen Lian, Dongxue Chen, Yuze Meng, Xiaotong Chen, Ying Su, Rounak Banerjee, Takashi Taniguchi, Kenji Watanabe, Sefaattin Tongay, Chuanwei Zhang, Yong-Tao Cui, Su-Fei Shi

Abstract: Moiré superlattices of semiconducting transition metal dichalcogenides (TMDCs) enable unprecedented spatial control of electron wavefunctions in an artificial lattice with periodicities more than ten times larger than that of atomic crystals, leading to emerging quantum states with fascinating electronic and optical properties. The breaking of translational symmetry further introduces a new degree… ▽ More Moiré superlattices of semiconducting transition metal dichalcogenides (TMDCs) enable unprecedented spatial control of electron wavefunctions in an artificial lattice with periodicities more than ten times larger than that of atomic crystals, leading to emerging quantum states with fascinating electronic and optical properties. The breaking of translational symmetry further introduces a new degree of freedom inside each moiré unit cell: high symmetry points of energy minima called moiré sites, behaving as spatially separated quantum dots. The superposition of a quasiparticle wavefunction between different moiré sites will enable a new platform for quantum information processing but is hindered by the suppressed electron tunneling between moiré sites. Here we demonstrate the superposition between two moiré sites by constructing an angle-aligned trilayer WSe2/monolayer WS2 moiré heterojunction. The two moiré sites with energy minimum allow the formation of two different interlayer excitons, with the hole residing in either moiré site of the first WSe2 layer interfacing the WS2 layer and the electron in the third WSe2 layer. An external electric field can drive the hybridization of either of the interlayer excitons with the intralayer excitons in the third WSe2 layer, realizing the continuous tuning of interlayer exciton hopping between two moiré sites. Therefore, a superposition of the two interlayer excitons localized at different moiré sites can be realized, which can be resolved in the electric-field-dependent optical reflectance spectra, distinctly different from that of the natural trilayer WSe2 in which the moiré modulation is absent. Our study illustrates a strategy of harnessing the new moiré site degree of freedom for quantum information science, a new direction of twistronics. △ Less

Submitted 21 August, 2023; originally announced August 2023.

Journal ref: Nature Communications 14, 5042 (2023)

Valley-polarized Exitonic Mott Insulator in WS2/WSe2 Moiré Superlattice

Authors: Zhen Lian, Yuze Meng, Lei Ma, Indrajit Maity, Li Yan, Qiran Wu, Xiong Huang, Dongxue Chen, Xiaotong Chen, Xinyue Chen, Mark Blei, Takashi Taniguchi, Kenji Watanabe, Sefaattin Tongay, Johannes Lischner, Yong-Tao Cui, Su-Fei Shi

Abstract: Strongly enhanced electron-electron interaction in semiconducting moiré superlattices formed by transition metal dichalcogenides (TMDCs) heterobilayers has led to a plethora of intriguing fermionic correlated states. Meanwhile, interlayer excitons in a type-II aligned TMDC heterobilayer moiré superlattice, with electrons and holes separated in different layers, inherit this enhanced interaction an… ▽ More Strongly enhanced electron-electron interaction in semiconducting moiré superlattices formed by transition metal dichalcogenides (TMDCs) heterobilayers has led to a plethora of intriguing fermionic correlated states. Meanwhile, interlayer excitons in a type-II aligned TMDC heterobilayer moiré superlattice, with electrons and holes separated in different layers, inherit this enhanced interaction and strongly interact with each other, promising for realizing tunable correlated bosonic quasiparticles with valley degree of freedom. We employ photoluminescence spectroscopy to investigate the strong repulsion between interlayer excitons and correlated electrons in a WS2/WSe2 moiré superlattice and combine with theoretical calculations to reveal the spatial extent of interlayer excitons and the band hierarchy of correlated states. We further find that an excitonic Mott insulator state emerges when one interlayer exciton occupies one moiré cell, evidenced by emerging photoluminescence peaks under increased optical excitation power. Double occupancy of excitons in one unit cell requires overcoming the energy cost of exciton-exciton repulsion of about 30-40 meV, depending on the stacking configuration of the WS2/WSe2 heterobilayer. Further, the valley polarization of the excitonic Mott insulator state is enhanced by nearly one order of magnitude. Our study demonstrates the WS2/WSe2 moiré superlattice as a promising platform for engineering and exploring new correlated states of fermion, bosons, and a mixture of both. △ Less

Submitted 24 August, 2023; v1 submitted 21 August, 2023; originally announced August 2023.

Measurements of Correlated Insulator Gaps in a Transition Metal Dichalcogenide Moiré Superlattice

Authors: Xiong Huang, Dongxue Chen, Zhen Lian, Qiran Wu, Mina Rashetnia, Mark Blei, Takashi Taniguchi, Kenji Watanabe, Sefaattin Tongay, Su-Fei Shi, Yong-Tao Cui

Abstract: Moiré superlattices of transitional metal dichalcogenides exhibit strong electron-electron interaction that has led to experimental observations of Mott insulators and generalized Wigner crystals. In this letter, we report direct measurements of the thermodynamic gaps of these correlated insulating states in a dual-gate WS2/WSe2 moiré bilayer. We employ the microwave impedance microscopy to probe… ▽ More Moiré superlattices of transitional metal dichalcogenides exhibit strong electron-electron interaction that has led to experimental observations of Mott insulators and generalized Wigner crystals. In this letter, we report direct measurements of the thermodynamic gaps of these correlated insulating states in a dual-gate WS2/WSe2 moiré bilayer. We employ the microwave impedance microscopy to probe the electronic features in both the graphene top gate and the moiré bilayer, from which we extract the doping dependence of the chemical potential of the moiré bilayer and the energy gaps for various correlated insulating states utilizing the Landau quantization of graphene. These gaps are relatively insensitive to the application of an external electric field to the WS2/WSe2 moiré bilayer. △ Less

Submitted 15 August, 2023; originally announced August 2023.

Antisymmetric Planar Hall Effect in Rutile Oxide Films Induced by the Lorentz Force

Authors: Yongwei Cui, Zhaoqing Li, Haoran Chen, Yue Chen, Yunzhuo Wu, Ke Pei, Tong Wu, Nian Xie, Renchao Che, Xuepeng Qiu, Yi Liu, Zhe Yuan, Yizheng Wu

Abstract: The conventional Hall effect is linearly proportional to the field component or magnetization component perpendicular to a film. Despite the increasing theoretical proposals on the Hall effect to the in-plane field or magnetization in various special systems induced by the Berry curvature, such an unconventional Hall effect has only been experimentally reported in Weyl semimetals and in a heterodi… ▽ More The conventional Hall effect is linearly proportional to the field component or magnetization component perpendicular to a film. Despite the increasing theoretical proposals on the Hall effect to the in-plane field or magnetization in various special systems induced by the Berry curvature, such an unconventional Hall effect has only been experimentally reported in Weyl semimetals and in a heterodimensional superlattice. Here, we report an unambiguous experimental observation of the antisymmetric planar Hall effect (APHE) with respect to the in-plane magnetic field in centrosymmetric rutile RuO2 and IrO2 single-crystal films. The measured Hall resistivity is found to be linearly proportional to the component of the applied in-plane magnetic field along a particular crystal axis and to be independent of the current direction or temperature. Both the experimental observations and theoretical calculations confirm that the APHE in rutile oxide films is induced by the Lorentz force. Our findings can be generalized to ferromagnetic materials for the discovery of anomalous Hall effects and quantum anomalous Hall effects induced by in-plane magnetization. In addition to significantly expanding knowledge of the Hall effect, this work opens the door to explore new members in the Hall effect family. △ Less

Submitted 2 June, 2024; v1 submitted 12 August, 2023; originally announced August 2023.