Showing 1–50 of 56 results for author: An, Y

Statistically Steady Holographic Quantum Turbulence: Hyperuniform Vortex Matter and Crossover

Authors: Yu-Ping An, Peng-Bo Ding, Zhen-Han Jin, Li Li

Abstract: A long-standing obstacle in quantum turbulence has been the difficulty of sustaining robust statistical steady states, preventing unambiguous identification of universal vortex organization and kinetic scaling. We construct such a steady state in two-dimensional holographic superfluid turbulence by continuous Landau-instability driving, sustaining ${\sim}2500$ vortices free from transient artifact… ▽ More A long-standing obstacle in quantum turbulence has been the difficulty of sustaining robust statistical steady states, preventing unambiguous identification of universal vortex organization and kinetic scaling. We construct such a steady state in two-dimensional holographic superfluid turbulence by continuous Landau-instability driving, sustaining ${\sim}2500$ vortices free from transient artifacts. The topological charge structure factor $S_c(k)$ reveals Class I disordered hyperuniformity with $S_c(k)\propto k^{α>1}$ as $k\to0$, where $k$ is the wavenumber. This constitutes the strongest long-range order of its kind and its first observation in a strongly driven, far-from-equilibrium quantum fluid with topological defects as the organizing principle, establishing a novel non-equilibrium vortex phase. Exploiting this platform, we resolve the scaling controversy: the apparent $k^{-5/3}$ signature in the kinetic energy spectrum is a narrow crossover between the $k^{-1}$ single-vortex and $k^{-3}$ core regimes, not a genuine Kolmogorov inertial range. The real-space second-order structure function provides decisive evidence via $S_2(r)\propto \ln r$ where $r$ is the spatial separation, with no $r^{2/3}$ Kolmogorov scaling, ruling out a true inertial cascade. These findings reveal that strongly coupled quantum turbulence lacks an inverse cascade due to the absence of macroscopic Onsager clusters, demonstrating energy transport fundamentally distinct from weakly coupled superfluids. △ Less

Submitted 17 August, 2026; originally announced August 2026.

Comments: 6 pages, 3 figures, and supplementary information

Probing intrinsic magnetic phases in low-dimensional nearly twin-free NiPS$_3$ single crystals

Authors: Yeochan An, Heejun Yang, Sung Jin Park, Giung Park, Woonghee Cho, Pyeongjae Park, Seokhwan Yun, Yoshimitsu Kohama, Je-Geun Park

Abstract: We report the intrinsic thermal and magnetic properties of the low-dimensional van der Waals (vdW) antiferromagnet NiPS$_3$ and explore its emergent magnetic phases by controlling crystallographic twinning. Using nearly twin-free crystals, we resolve intrinsic properties that are typically obscured by multidomain effects in bulk samples. Magnetization results reveal a highly anisotropic, sharp spi… ▽ More We report the intrinsic thermal and magnetic properties of the low-dimensional van der Waals (vdW) antiferromagnet NiPS$_3$ and explore its emergent magnetic phases by controlling crystallographic twinning. Using nearly twin-free crystals, we resolve intrinsic properties that are typically obscured by multidomain effects in bulk samples. Magnetization results reveal a highly anisotropic, sharp spin-flop transition, confirming the high domain purity of our crystals. Furthermore, high-precision thermodynamic and transport data reveal a broad fluctuation regime around the Néel temperature ($T_{\mathrm{N}}$ = 157.5 K), with a heat capacity anomaly and a concurrent suppression of thermal conductivity. Field-dependent thermal transport shows a small but distinct contribution from spin-lattice coupling, as evidenced by the dip at the spin-flop transition. We develop a theoretical model to explain these properties reported in this paper, with good agreement between experiment and theory. Our work establishes a definitive baseline for bulk properties of NiPS$_3$ and demonstrates the feasibility of resolving intrinsic anisotropies by addressing crystallographic twinning in vdW magnets. △ Less

Submitted 14 August, 2026; originally announced August 2026.

Comments: Accepted by Advanced Functional Materials; 27 pages, 6 main figures, 8 supporting figures

Ah-SCDFT:A general approach for superconductivity with an-harmonic corrections

Authors: Xiaozheng Fan, Panshi Jing, Chuanguang Zhang, Junshuai Wang, Chunlan Ma, Shijing Gong, Chuanxi Zhao, Tianxing Wang, Yipeng An

Abstract: First-principles studies of superconductivity often neglect anharmonic effects (AHE), despite their crucial role in achieving quantitative accuracy in many materials. To bridge this gap, we introduce a general computational approach, termed anharmonic superconducting density functional theory (ah-SCDFT) which systematically incorporates anharmonic corrections into standard SCDFT. This approach all… ▽ More First-principles studies of superconductivity often neglect anharmonic effects (AHE), despite their crucial role in achieving quantitative accuracy in many materials. To bridge this gap, we introduce a general computational approach, termed anharmonic superconducting density functional theory (ah-SCDFT) which systematically incorporates anharmonic corrections into standard SCDFT. This approach allows for high-fidelity predictions of superconducting properties with only a modest increase in computational cost for a limited number of superconducting calculation convergence steps. We demonstrate the effectiveness and reliability of ah-SCDFT by applying it to the prototypical superconductor MgB2, accurately reproducing its superconducting behavior under both ambient conditions and applied pressure in excellent agreement with experiment. Our results establish ah-SCDFT as a powerful, efficient, and broadly applicable approach for quantitatively reliable studies of superconductivity and a promising tool for the prediction of new superconducting materials. △ Less

Submitted 20 July, 2026; originally announced July 2026.

Comments: 7 pages, 4 figures

Journal ref: Physical Review B 113, 214521 (2026)

Interfacial chirality-induced magnetic-field-free switching with high energy efficiency in all-vdW heterostructures

Authors: Kai-Xuan Zhang, Suik Cheon, Seungbok Lee, Joonyoung Choi, Jihoon Keum, Hyuncheol Kim, Yeochan An, Woonghee Cho, Suhan Son, Jingyuan Cui, Pyeongjae Park, Younjung Jo, Jun Sung Kim, Hyun-Woo Lee, Je-Geun Park

Abstract: Chirality, a central concept across many scientific disciplines, continues to inspire the discovery of novel physical phenomena. In condensed matter physics, structural chirality - defined by the absence of mirror plane symmetries - has primarily been explored in bulk materials. However, new chiral phenomena can emerge uniquely at the interface, distinct from their bulk counterparts, when a chiral… ▽ More Chirality, a central concept across many scientific disciplines, continues to inspire the discovery of novel physical phenomena. In condensed matter physics, structural chirality - defined by the absence of mirror plane symmetries - has primarily been explored in bulk materials. However, new chiral phenomena can emerge uniquely at the interface, distinct from their bulk counterparts, when a chiral material forms a heterostructure. Here, we demonstrate that all van-der-Waals (vdW) heterostructure composed of the chiral Co1/3TaS2 and the achiral vdW ferromagnet Fe3GeTe2 exhibits two distinct and unconventional spin-orbit torques originating from the interfacial chirality. These torques enable magnetic-field-free switching of perpendicular magnetization with ultralow current density ~ 10^6 A/cm^2 and minimal power dissipation < 10^15 W/m^3. Moreover, by replacing Fe3GeTe2 with a similar vdW ferromagnet, Fe3GaTe2, but of higher Curie temperature, we achieved the magnetic-field-free switching at room temperature in the Fe3GaTe2/Co1/3TaS2 vdW heterostructure. Our findings establish interfacial chirality as a powerful new handle for spintronic control, opening a new pathway to explore chirality-induced phenomena beyond the bulk symmetry constraints - and paving the way toward highly efficient, low-power spintronic devices based on all-vdW heterostructures. △ Less

Submitted 8 July, 2026; originally announced July 2026.

Comments: Accepted by Nature Communications; 30 pages; 4 main figures; 12 supporting figures

Journal ref: Nature Communications 17, 8620 (2026)

Predicting Novel Stable Materials for Experimental Synthesis

Authors: Yuqi An, Sihong Zhu, Joseph Montoya, Xingyu Guo, Zhenbin Wang

Abstract: Machine-learning-accelerated materials discovery has yielded large numbers of computationally stable compounds, yet many remain experimentally unrealized, underscoring a persistent gap between prediction and synthesis. Here, we introduce a hierarchical screening framework that combines PBE-based thermodynamic stability, efficient dynamical-stability screening enabled by universal machine-learning… ▽ More Machine-learning-accelerated materials discovery has yielded large numbers of computationally stable compounds, yet many remain experimentally unrealized, underscoring a persistent gap between prediction and synthesis. Here, we introduce a hierarchical screening framework that combines PBE-based thermodynamic stability, efficient dynamical-stability screening enabled by universal machine-learning interatomic potentials, and SCAN-based thermodynamic refinement. Applying this protocol to the 894 stable materials previously reported in Sci. Data 9, 302 (2022), we first curate 603 unique structures, of which only 298 remain thermodynamically stable on the complete PBE phase diagrams, demonstrating the critical role of competing phases in stability assessment. Dynamical screening then identifies 166 materials stable under both harmonic-phonon and finite-temperature molecular dynamics criteria, and SCAN phase diagrams further narrow this set to 109. Finally, by combining decomposition enthalpy with chemical-space completeness, we prioritize 25 candidates as high-confidence targets for experimental synthesis. This work provides a practical protocol for translating stability predictions into experimentally actionable synthesis targets, closing a key gap in machine-learning-driven materials discovery. △ Less

Submitted 2 July, 2026; originally announced July 2026.

Comments: 28 pages, 7 figures

Melt-Quench Failures and Practical Solutions for Universal Machine-Learning Interatomic Potentials in Amorphous Structure Generation

Authors: Shuwei Li, Yuqi An, Xingyu Guo, Wenqiang Yang, Zhenbin Wang

Abstract: Generating experimentally relevant amorphous structures via melt-quench molecular dynamics is prohibitively expensive at the first-principles level. Universal machine-learning interatomic potentials (uMLIPs) could accelerate such simulations, but their reliability under non-equilibrium conditions remains unclear. Here, we examine eight leading uMLIPs for generating amorphous IrO2, using this elect… ▽ More Generating experimentally relevant amorphous structures via melt-quench molecular dynamics is prohibitively expensive at the first-principles level. Universal machine-learning interatomic potentials (uMLIPs) could accelerate such simulations, but their reliability under non-equilibrium conditions remains unclear. Here, we examine eight leading uMLIPs for generating amorphous IrO2, using this electrocatalytically relevant oxide as a diagnostic case. Under the conventional melt-quench protocol, all models yield unphysically expanded structures with densities of 1-4 g/cm3, far below the ab initio molecular dynamics (AIMD) reference value of 10.04 g/cm3. Comparisons against ab initio references show that accurate energies and forces alone do not ensure stable NPT dynamics; correct energy-volume responses and pressure predictions are also essential. We identify two practical remedies: pressure-targeted fine-tuning and a revised NVT-quench/NPT-equilibration protocol that avoids unphysical volume expansion without additional ab initio training data. Both recover IrO2 densities and local structures consistent with AIMD. Across 30 chemically diverse materials, the volume-expansion failure proves general, and the revised protocol substantially improves density predictions, reducing the AIMD-referenced MAE from 2.46 to 0.35 g/cm3. This work establishes practical validation criteria and simulation strategies for robust uMLIP-driven amorphous structure generation. △ Less

Submitted 16 July, 2026; v1 submitted 15 June, 2026; originally announced June 2026.

Bubble dynamics and vortex formation in holographic first-order superfluid phase transitions

Authors: Zhen-han Jin, Yu-ping An, Li Li

Abstract: We investigate bubble dynamics in a holographic superfluid undergoing a first-order phase transition with spontaneous $U(1)$ symmetry breaking. Near the nucleation threshold, the system exhibits universal critical behavior governed by a single unstable mode, leading to logarithmic scaling of the time spent near the critical solution. The terminal bubble wall velocity increases with charge density… ▽ More We investigate bubble dynamics in a holographic superfluid undergoing a first-order phase transition with spontaneous $U(1)$ symmetry breaking. Near the nucleation threshold, the system exhibits universal critical behavior governed by a single unstable mode, leading to logarithmic scaling of the time spent near the critical solution. The terminal bubble wall velocity increases with charge density but remains small due to strong dissipation. In multi-bubble collisions, vortex formation depends sensitively on the initial phases and deviates significantly from the geodesic rule. Notably, we identify a regime where three-bubble collisions produce a vortex-antivortex pair that subsequently annihilates, a phenomenon not predicted by the geodesic rule. The lifetime of this pair scales logarithmically with the distance to the critical collision radius. Our results underscore the crucial role of non-equilibrium dynamics in strongly coupled superfluids and provide new insights into topological defect formation during first-order phase transitions. △ Less

Submitted 18 April, 2026; originally announced April 2026.

Composition-dependent bulk properties of intercalated transition metal dichalcogenides $Co_{1/3(1\pmδ)}NbS_{2}$

Authors: Woonghee Cho, Kiwan Nam, Yeochan An, You Young Kim, Myung-Hwa Jung, Kee Hoon Kim, Je-Geun Park

Abstract: We report a systematic study of the composition-dependent bulk properties in $Co_{1/3(1\pmδ)}NbS_{2}$ single crystals across a series of precisely controlled cobalt compositions with -4%<$δ$<8%. By tuning the cobalt stoichiometry, we find that the topological Hall effect is critically sensitive to the intercalant cobalt composition and is completely suppressed when the cobalt composition exceeds… ▽ More We report a systematic study of the composition-dependent bulk properties in $Co_{1/3(1\pmδ)}NbS_{2}$ single crystals across a series of precisely controlled cobalt compositions with -4%<$δ$<8%. By tuning the cobalt stoichiometry, we find that the topological Hall effect is critically sensitive to the intercalant cobalt composition and is completely suppressed when the cobalt composition exceeds $δ$=+4%. We observe that the longitudinal conductivity is also strongly influenced by the cobalt composition, reaching its maximum value just before the disappearance of the topological Hall effect. Furthermore, heat capacity measurements reveal distinct Sommerfeld coefficients ($γ$) across different compositions, which exhibit a clear linear scaling with the inverse of the ordinary Hall coefficient ($R_H^{-1}$). These results demonstrate that composition tuning in $Co_{1/3(1\pmδ)}NbS_{2}$ systematically modifies the low-energy electronic degree of freedom, moving beyond a simple dilute impurity picture. Finally, we use the microscopic spin Hamiltonian to explain the stability of experimentally observed M-point modulation vector and the corresponding triple-Q magnetic order. Our findings highlight that the topological properties of this system are highly tunable through precise control of the intercalant concentration, offering a new perspective on the competition between electronic and magnetic orders in intercalated transition-metal dichalcogenides. △ Less

Submitted 31 March, 2026; v1 submitted 27 March, 2026; originally announced March 2026.

Comments: 16 pages, 8 figures

Accelerating Complex Materials Discovery with Universal Machine-Learning Potential-Driven Structure Prediction

Authors: Yuqi An, Zhenbin Wang

Abstract: Universal machine-learning interatomic potentials (uMLIPs) have become powerful tools for accelerating computational materials discovery by replacing expensive first-principles calculations in crystal structure prediction (CSP). However, their effectiveness in identifying new, complex materials remains uncertain. Here, we systematically assess the capability of a uMLIP (i.e.,M3GNet) to accelerate… ▽ More Universal machine-learning interatomic potentials (uMLIPs) have become powerful tools for accelerating computational materials discovery by replacing expensive first-principles calculations in crystal structure prediction (CSP). However, their effectiveness in identifying new, complex materials remains uncertain. Here, we systematically assess the capability of a uMLIP (i.e.,M3GNet) to accelerate CSP in quaternary oxides. Through extensive exploration of the Sr-Li-Al-O and Ba-Y-Al-O systems, we show that uMLIP can rediscover experimentally known materials absent from its training set and identify seven new thermodynamically and dynamically stable compounds. These include a new polymorph of Sr2LiAlO4 (P3221) and a new disordered phase, Sr2Li4Al2O7 (P1_bar). Furthermore, our results show stability predictions based on the semilocal PBE functional require cross-validation with higher-level methods, such as SCAN and RPA, to ensure reliability. While uMLIPs substantially reduce the computational cost of CSP, the primary bottleneck has shifted to the efficiency of search algorithms in navigating complex structural spaces. This work highlights both the promise and current limitations of uMLIP-driven CSP in the discovery of new materials. △ Less

Submitted 3 February, 2026; originally announced February 2026.

Journal ref: Materials Today Energy, 54, 102059 (2025)

Effect of superconductivity by Nb and V substitution in kagome CaPd5

Authors: Dan Li, Zhengxuan Wang, Chuanguang Zhang, Chunlan Ma, Shijing Gong, Chuanxi Zhao, Shuaikang Zhang, Tianxing Wang, Xiao Dong, Wuming Liu, Yipeng An

Abstract: Materials featuring kagome lattices have attracted significant research interest due to their unique geometric frustration, which gives rise to rich physical phenomena such as non-trivial topology, spin fluctuations, and superconductivity. In this work, using CaPd5 as the prototype structure, we discover and systematically investigate a new class of kagome superconductors, CaMxPd5-x (M = Nb and V)… ▽ More Materials featuring kagome lattices have attracted significant research interest due to their unique geometric frustration, which gives rise to rich physical phenomena such as non-trivial topology, spin fluctuations, and superconductivity. In this work, using CaPd5 as the prototype structure, we discover and systematically investigate a new class of kagome superconductors, CaMxPd5-x (M = Nb and V) alloys. First-principles calculations confirm that these compounds are non-magnetic metals, among which four are dynamically stable: CaNb5, CaV5, CaNb2Pd3, and CaV2Pd3. CaNb5 is identified as a strong electron-phonon coupling (EPC) superconductor with the highest superconducting transition temperature (Tc) of 10.1 K, which can be further increased to 12.8 K under external pressure. In contrast, CaV5, CaNb2Pd3, and CaV2Pd3 exhibit weaker EPC and correspondingly lower Tc values. Furthermore, by applying the method of symmetry indicators, we systematically classify the topological and nodal characteristics of CaNb5, providing valuable insights for determining its superconducting pairing symmetry. Our findings demonstrate that Nb and V substitution in kagome CaPd5 provides an effective route for designing a new type of kagome superconductor with relatively high Tc. This study also offers new perspectives on topological superconductivity in kagome systems and establishes a useful guideline for discovering other superconducting materials with unique properties. △ Less

Submitted 26 December, 2025; originally announced December 2025.

Comments: 4 figures

Journal ref: Superconductor Science and Technology 2025

Martini Mapper: An Automated Fragment-Based Framework for Developing Coarse-Grained Models within the Martini 3 Framework

Authors: Kevin V. Bigting, Shubhadeep Nag, Yaxin An

Abstract: Coarse-graining (CG) reduces molecular details to extend the time and length scales of molecular dynamics simulations to microseconds and micrometers. However, the CG approaches have long been limited by the difficulty of constructing both accurate and transferable models efficiently, considering the large diversity of chemical structures of materials. Among CG force fields, Martini is the most wi… ▽ More Coarse-graining (CG) reduces molecular details to extend the time and length scales of molecular dynamics simulations to microseconds and micrometers. However, the CG approaches have long been limited by the difficulty of constructing both accurate and transferable models efficiently, considering the large diversity of chemical structures of materials. Among CG force fields, Martini is the most widely used, as it retains essential chemical features while offering substantial computational efficiency. Its most recent version, Martini 3, expands chemical resolution through a much broader bead set, particularly for small molecules. However, this flexibility also complicates the mapping of organic molecules because of context-dependent rules and the lack of standardized procedures. To address this issue, we present an automated framework that builds Martini 3 models directly from SMILES (Simplified Molecular Input Line Entry System) strings by combining a curated bead dictionary with a hierarchical, rule-based algorithm and molecule-specific bonded parameters. Our framework, Martini Mapper https://github.com/eliobaby/Martini_mapper, generated Martini 3 models for 6,280 molecules across six chemically diverse datasets, including 1,689 systems with bond/angle parameters and additional large systems mapped at the topological level. A curated subset of 1,075 mapped structures was benchmarked using transfer free energies in hydrated octanol, hexadecane, and chloroform from water against reference data wherever available. We further examined the benchmark with structural validation via SASA, yielding good agreement with experimental and atomistic reference data. The workflow can also map large molecules containing up to 172 heavy atoms, exceeding the capabilities of existing automated approaches. Our framework, therefore, enables Martini 3 structures for high-throughput simulations. △ Less

Submitted 24 March, 2026; v1 submitted 14 November, 2025; originally announced November 2025.

Controlling GaN nucleation via O$_2$-plasma-perforated graphene masks on c-plane sapphire

Authors: Su Young An, Chinkyo Kim

Abstract: Atomically thin, perforated graphene on $c$-plane sapphire functions as a nanoscale mask that enables GaN growth through thru-holes. We tune the perforated-area fraction $f_p$ by controlled O$_2$-plasma exposure and quantify its impact on early-stage nucleation: the nucleation-site density scales with $f_p$, while the nucleation-delay time decreases approximately as $1/f_p$. Time-resolved areal co… ▽ More Atomically thin, perforated graphene on $c$-plane sapphire functions as a nanoscale mask that enables GaN growth through thru-holes. We tune the perforated-area fraction $f_p$ by controlled O$_2$-plasma exposure and quantify its impact on early-stage nucleation: the nucleation-site density scales with $f_p$, while the nucleation-delay time decreases approximately as $1/f_p$. Time-resolved areal coverage and domain counts exhibit systematic $f_p$-dependent trends. A kinetic Monte Carlo (kMC) model that coarse-grains atomistic events -- adatom arrival, surface diffusion, attachment at exposed sapphire within perforations, and coalescence (the first front-front contact between laterally growing domains) -- reproduces these trends using a constant per-site nucleation rate. Fitting the kMC simulation data yields onset times t$_0$ for the nucleation delay that closely match independently observed no-growth thresholds (Set 1: 28.5s vs $\sim$30s; Set 2: 38s vs $\sim$35s), validating the kMC-experiment mapping and highlighting plasma dose as an activation threshold for plasma-induced through-hole formation in 2D materials. Together, experiment and kMC identify $f_p$ as a single, surface-engineerable parameter governing GaN nucleation statistics on perforated graphene masks, providing a quantitative basis and process window for epitaxial lateral overgrowth (ELOG)/thru-hole epitaxy (THE) workflows that employ two-dimensional masks. △ Less

Submitted 10 September, 2025; originally announced September 2025.

Corner-Sharing PS$_4$-BS$_4$ Modes Facilitate Fast Ion Conduction in Lithium Thioborophosphate Iodide Glassy Solid Electrolytes

Authors: Yun An

Abstract: Glassy solid electrolytes (GSEs), with their amorphous nature and the absence of grain boundaries, make them highly attractive for applications in all-solid-state lithium batteries (ASSLBs), a leading candidate for next-generation energy storage technologies. A recently developed lithium thioborophosphate iodide GSE, composed of 30Li$_2$S-25B$_2$S$_3$-45LiI-5P$_2$S$_5$ (LBPSI), has demonstrated ex… ▽ More Glassy solid electrolytes (GSEs), with their amorphous nature and the absence of grain boundaries, make them highly attractive for applications in all-solid-state lithium batteries (ASSLBs), a leading candidate for next-generation energy storage technologies. A recently developed lithium thioborophosphate iodide GSE, composed of 30Li$_2$S-25B$_2$S$_3$-45LiI-5P$_2$S$_5$ (LBPSI), has demonstrated excellent room-temperature ionic conductivity and low activation energy. Despite this exciting finding, the underlying mechanism behind this ultrafast ion transport remains ambiguous. Here, we accurately fine-tune the foundational MACE-MP-0 model and perform large-scale machine learning molecular dynamics simulations to investigate the structural and ion dynamics in LBPSI GSE. Our results reveal that B$_2$S$_3$ glass formers primarily form multi-bridged B$_x$S$_y$ long-chain networks that impede Li$^+$ conduction. In contrast, P$_2$S$_5$ gives rise to mono-tetrahedral PS$_4$$^{3-}$ and di-tetrahedral P$_2$S$_7$$^{4-}$ tetrahedra, which engage in distinctive corner-sharing modes with BS$_4$$^{5-}$ tetrahedra, effectively disrupting the B$_x$S$_y$ chains and enhancing Li$^+$ mobility. Furthermore, the polyhedral anion rotations of PS$_4$$^{3-}$ and BS$_4$$^{5-}$ in the corner-sharing PS$_4$-BS$_4$ motifs may further promote fast Li$^+$ conduction. △ Less

Submitted 10 July, 2025; originally announced July 2025.

Machine Learning Reveals Composition Dependent Thermal Stability in Halide Perovskites

Authors: Abigail R. Hering, Mansha Dubey, Elahe Hosseini, Meghna Srivastava, Yu An, Juan-Pablo Correa-Baena, Houman Homayoun, Marina S. Leite

Abstract: Halide perovskites exhibit unpredictable properties in response to environmental stressors, due to several composition-dependent degradation mechanisms. In this work, we apply data visualization and machine learning (ML) techniques to reveal unexpected correlations between composition, temperature, and material properties while using high throughput, in situ environmental photoluminescence (PL) ex… ▽ More Halide perovskites exhibit unpredictable properties in response to environmental stressors, due to several composition-dependent degradation mechanisms. In this work, we apply data visualization and machine learning (ML) techniques to reveal unexpected correlations between composition, temperature, and material properties while using high throughput, in situ environmental photoluminescence (PL) experiments. Correlation heatmaps show the strong influence of Cs content on film degradation, and dimensionality reduction visualization methods uncover clear composition-based data clusters. An extreme gradient boosting algorithm (XGBoost) effectively forecasts PL features for ten perovskite films with both composition-agnostic (>85% accuracy) and composition-dependent (>75% accuracy) model approaches, while elucidating the relative feature importance of composition (up to 99%). This model validates a previously unseen anti-correlation between Cs content and material thermal stability. Our ML-based framework can be expanded to any perovskite family, significantly reducing the analysis time currently employed to identify stable options for photovoltaics. △ Less

Submitted 23 April, 2025; v1 submitted 4 April, 2025; originally announced April 2025.

Comments: 21 pages, 5 figures

Symmetry-Constrained Anomalous Transport in the Altermagnetic Material CuX$_2$ (X=F,Cl)

Authors: Zhengxuan Wang, Ruqian Wu, Chunlan Ma, Shijing Gong, Shuaikang Zhang, Guangtao Wang, Tianxing Wang, Yipeng An

Abstract: Recently discovered, altermagnetism represents a third class of collinear magnets. These materials exhibit zero net magnetization, similar to antiferromagnets, but display anomalous transport properties resembling those of ferromagnets. Altermagnetic materials manifest various anomalous electronic transport phenomena, including the anomalous Hall effect, anomalous Nernst effect, and anomalous ther… ▽ More Recently discovered, altermagnetism represents a third class of collinear magnets. These materials exhibit zero net magnetization, similar to antiferromagnets, but display anomalous transport properties resembling those of ferromagnets. Altermagnetic materials manifest various anomalous electronic transport phenomena, including the anomalous Hall effect, anomalous Nernst effect, and anomalous thermal Hall effect. Additionally, they exhibit magneto-optical Kerr and Faraday effects, previously considered exclusive to ferromagnetic materials. These anomalous transport phenomena are constrained by symmetry, as revealed by density functional theory (DFT) calculations. However, an effective model-based approach to verify these symmetry constraints remains unavailable. In this Letter, we construct a $k\cdot p$ model for $d$-wave altermagnets CuX$_2$ (X=F,Cl) using spin space group representations and apply it to calculate the anomalous Hall effect. The symmetry-imposed transport properties predicted by the model are in agreement with the DFT results, providing a foundation for further investigation into symmetry-restricted transport phenomena in altermagnetic materials. △ Less

Submitted 24 March, 2025; originally announced March 2025.

Comments: 6 pages, 4 figures

Current-driven collective control of helical spin texture in van der Waals antiferromagnet

Authors: Kai-Xuan Zhang, Suik Cheon, Hyuncheol Kim, Pyeongjae Park, Yeochan An, Suhan Son, Jingyuan Cui, Jihoon Keum, Joonyoung Choi, Younjung Jo, Hwiin Ju, Jong-Seok Lee, Youjin Lee, Maxim Avdeev, Armin Kleibert, Hyun-Woo Lee, Je-Geun Park

Abstract: Electrical control of quantum magnetic states is essential in spintronic science. Initial studies on the ferromagnetic state control were extended to collinear antiferromagnets and, more recently, noncollinear antiferromagnets. However, electrical control mechanisms of such exotic magnetic states remain poorly understood. Here, we report the first experimental and theoretical example of the curren… ▽ More Electrical control of quantum magnetic states is essential in spintronic science. Initial studies on the ferromagnetic state control were extended to collinear antiferromagnets and, more recently, noncollinear antiferromagnets. However, electrical control mechanisms of such exotic magnetic states remain poorly understood. Here, we report the first experimental and theoretical example of the current control of helical antiferromagnets, arising from the competition between collinear antiferromagnetic exchange and interlayer Dzyaloshinskii-Moriya interaction in new van-der-Waals (vdW) material Ni1/3NbS2. Due to the intrinsic broken inversion symmetry, an in-plane current generates spin-orbit torque that, in turn, interacts directly with the helical antiferromagnetic order. Our theoretical analyses indicate that a weak ferromagnetic order coexists due to the Dzyaloshinskii-Moriya interaction, mediating the spin-orbit torque to collectively rotate the helical antiferromagnetic order. Our Ni1/3NbS2 nanodevice experiments produce current-dependent resistance change consistent with the theoretical prediction. This work widens our understanding of the electrical control of helical antiferromagnets and promotes vdW quantum magnets as interesting material platforms for electrical control. △ Less

Submitted 28 February, 2025; originally announced March 2025.

Comments: Accepted by Physical Review Letters; 41 pages, 4 main figures, 12 supporting figures

Journal ref: Physical Review Letters XX, XXXX (2025)

MPd5 kagome superconductors studied by density functional calculations

Authors: Dan Li, Zhengxuan Wang, Panshi Jing, Mehrdad Shiri, Kun Wang, Chunlan Ma, Shijing Gong, Chuanxi Zhao, Tianxing Wang, Xiao Dong, Lin Zhuang, Wuming Liu, Yipeng An

Abstract: Kagome materials, which are composed of hexagons tiled with a shared triangle, have inspired enormous interest due to their unique structures and rich physical properties; exploring superconducting material systems with new kagome structures is still an important research direction. Here, we predict a type of kagome superconductor, MPd5 (M is a group-IIA metal element), and identify that it exhibi… ▽ More Kagome materials, which are composed of hexagons tiled with a shared triangle, have inspired enormous interest due to their unique structures and rich physical properties; exploring superconducting material systems with new kagome structures is still an important research direction. Here, we predict a type of kagome superconductor, MPd5 (M is a group-IIA metal element), and identify that it exhibits coexistence of superconductivity and nontrivial topological properties. We uncover its phonon-mediated superconductivity by the density functional theory for superconductors, predicting the superconducting transition temperatures (Tc) of 2.64, 2.03, and 1.50 K for CaPd5, SrPd5, and BaPd5, respectively. These Tc can be effectively tuned through the application of external pressure and electron doping. The present results also demonstrate that MPd5 have topological properties; e.g., CaPd5 shows topological nontrivial intersection near the Fermi level (EF). Our results indicate that MPd5 materials can be an emerging material platform with rich exotic physics in their kagome structures, and render themselves excellent candidates for superconducting and advanced functional materials that could be utilized in topological quantum computing and information technology. △ Less

Submitted 2 May, 2025; v1 submitted 21 February, 2025; originally announced February 2025.

Comments: 11 pages, 5 figures

MSC Class: https://doi.org/10.1103/PhysRevB.111.144511

Journal ref: Physical Review B 111, 144511 (2025)

Kitaev interaction and proximate higher-order skyrmion crystal in the triangular lattice van der Waals antiferromagnet NiI2

Authors: Chaebin Kim, Olivia Vilella, Youjin Lee, Pyeongjae Park, Yeochan An, Woonghee Cho, Matthew B. Stone, Alexander I. Kolesnikov, Yiquing Hao, Shinichiro Asai, Shinichi Itoh, Takatsugu Masuda, Sakib Matin, Sujin Kim, Sung-Jin Kim, Martin Mourigal, Je-Geun Park

Abstract: Topological spin textures, such as magnetic skyrmions, are a spectacular manifestation of magnetic frustration and anisotropy. Most known skyrmion systems are restricted to a topological charge of one, require an external magnetic field for stabilization, and are only reported in a few materials. Here, we investigate the possibility that the Kitaev anisotropic-exchange interaction stabilizes a hig… ▽ More Topological spin textures, such as magnetic skyrmions, are a spectacular manifestation of magnetic frustration and anisotropy. Most known skyrmion systems are restricted to a topological charge of one, require an external magnetic field for stabilization, and are only reported in a few materials. Here, we investigate the possibility that the Kitaev anisotropic-exchange interaction stabilizes a higher-order skyrmion crystal in the insulating van der Waals magnet NiI2. We unveil and explain the incommensurate static and dynamic magnetic correlations across three temperature-driven magnetic phases of this compound using neutron scattering measurements, simulations, and modeling. Our parameter optimisation yields a minimal Kitaev-Heisenberg Hamiltonian for NiI2 which reproduces the experimentally observed magnetic excitations. Monte Carlo simulations for this model predict the emergence of the higher-order skyrmion crystal but neutron diffraction and optical experiments in the candidate intermediate temperature regime are inconclusive. We discuss possible deviations from the Kitaev-Heisenberg model that explains our results and conclude that NiI2, in addition to multiferroic properties in the bulk and few-layer limits, is a Kitaev bulk material proximate to the finite temperature higher-order skyrmion crystal phase. △ Less

Submitted 19 May, 2025; v1 submitted 19 February, 2025; originally announced February 2025.

Comments: 9 pages, 4 figures, including supplementary information

DFT+DMFT study on pressure-induced valence instability of CeCoSi

Authors: Shuai-Kang Zhang, Yuanji Xu, Guojun Li, Junshuai Wang, Zhongpo Zhou, Yipeng An

Abstract: Rare-earth compounds RCoSi exhibit unique properties, with distinct structural behaviors depending on whether R is a light, middle or heavy rare-earth element. Among them, CeCoSi undergoes a structural phase transition under high pressure, with the phase transition pressure increasing as temperature rises. Some experimental studies suggest that the transition is closely related to the behavior of… ▽ More Rare-earth compounds RCoSi exhibit unique properties, with distinct structural behaviors depending on whether R is a light, middle or heavy rare-earth element. Among them, CeCoSi undergoes a structural phase transition under high pressure, with the phase transition pressure increasing as temperature rises. Some experimental studies suggest that the transition is closely related to the behavior of Ce-4f electrons. In this work, we systematically studied the evolution of the electronic structure of CeCoSi with temperature and pressure. First, we used the DFT+DMFT to calculate the energy-volume curve of CeCoSi, which was in good agreement with the experimental results and far superior to the DFT method. Next, we studied the electronic structure of CeCoSi under different pressures and temperatures using DFT+DMFT. Our results show that CeCoSi is a Kondo metal with hybridization of Ce-4f and Co-3d. As pressure increases, the renormalization factor Z of Ce-4f5/2 increases, the occupancy number of Ce-4f electrons decreases, and CeCoSi transitions to a mixed-valence state at ~5.5 GPa in 100 K. The pressure of the quantum phase transition PQ is slightly higher than the experimentally observed structural phase transition pressure PS, and the PQ increases with increasing temperature, which is consistent with the behavior of PS in experiment. In addition, the hybridization strength of Ce-4f in the mixed-valence state is significantly greater than in the Kondo metal state. Our results suggest that the valence instability of Ce-4f is the cause of the structural phase transition. As pressure increases, Ce-4f electrons delocalize and CeCoSi transitions to mixed-valence state. This valence instability may cause redistribution of electron density, thus inducing a structural phase transition. Our work reveals the cause of the structural phase transition of CeCoSi under high pressure. △ Less

Submitted 15 March, 2025; v1 submitted 19 February, 2025; originally announced February 2025.

Comments: 15 pages, 6 figures

Splitting dynamics of quantized composite vortices in holographic miscible binary superfluids

Authors: Yuping An, Li Li

Abstract: The stability properties and splitting dynamics of multiply quantized vortices are the subject of interest in both theoretical and experimental investigations. Going beyond the regime of validity of Gross-Pitaevskii equation (GPE), we study the composite vortices in miscible strongly interacting binary superfluids by employing a holographic model that naturally incorporate finite temperature and d… ▽ More The stability properties and splitting dynamics of multiply quantized vortices are the subject of interest in both theoretical and experimental investigations. Going beyond the regime of validity of Gross-Pitaevskii equation (GPE), we study the composite vortices in miscible strongly interacting binary superfluids by employing a holographic model that naturally incorporate finite temperature and dissipation. The composite vortices is classified in terms of an integer pair $(S_1, S_2)$ of phase winding numbers and can share the same vortex core, while either co-rotating or counter-rotating, leading to very diverse vortex structures. We uncover different dynamical behaviors compared to results from GPE that is valid in weak coupling limit and zero temperature. In particular, we show that the occurrence of dynamic instabilities and the instability strength are sensitive to the temperature. We identify several temperature dependent dynamical transitions in $(1,1)$, $(2,\pm 1)$ and $(2,2)$ vortices. The splitting behaviors associated with different multipolarities are demonstrated by solving the full-time evolution for slightly perturbed composite vortices. We find that the final states of all composite vortices are generally singly quantized vortices, and no additional long living vortex is formed due to strong dissipation. Our results highlight the important role of temperature and the distinction between dynamics of composite vortices in weakly interacting superfluids without dissipation and strongly interacting case with dissipation, shedding a new light on the understanding of quantum vortex and dynamical instabilities in multicomponent superfluids. △ Less

Submitted 7 January, 2025; originally announced January 2025.

Comments: 22 pages, 12 figures

Journal ref: https://link.springer.com/article/10.1007/JHEP05(2025)007

Observing Li Nucleation at Li Metal-Solid Electrolyte Interface in All-Solid-State Batteries

Authors: Yun An, Taiping Hu, Quanquan Pang, Shenzhen Xu

Abstract: Benefiting from the significantly improved energy density and safety, all-solid-state lithium batteries (ASSLBs) are considered one of the most promising next-generation energy technologies. Their practical applications, however, are strongly impeded by the Li dendrite formation. Despite this recognized challenge, a comprehensive understanding of Li dendrite nucleation and formation mechanism rema… ▽ More Benefiting from the significantly improved energy density and safety, all-solid-state lithium batteries (ASSLBs) are considered one of the most promising next-generation energy technologies. Their practical applications, however, are strongly impeded by the Li dendrite formation. Despite this recognized challenge, a comprehensive understanding of Li dendrite nucleation and formation mechanism remains elusive. In particular, the initial locations of Li dendrite formation are still ambiguous: do Li clusters form directly at the Li anode surface, or inside the bulk solid electrolyte (SE), or within the solid-electrolyte interphase (SEI)? Here, based on the deep-potential molecular dynamics simulations combined with enhanced sampling techniques, we investigate the atomic-level mechanism of Li cluster nucleation and formation at the Li anode/SE interface. We observe that an isolated Li cluster initially forms inside the SEI between the Li6PS5Cl SE and the Li metal anode, located ~1 nm away from the Li anode/SEI boundary. The local electronic structure of the spontaneously formed SEI is found to be a key factor enabling the Li cluster formation within SEI, in which a significantly decreased bandgap could facilitate electronic conduction through the SEI and reduce Li+ ions to metallic Li atoms therein. Our work therefore provides atomic-level insights into Li-dendrite nucleation at anode/SE interfaces in ASSLBs, and could guide future design for developing Li-dendrite-inhibiting strategies. △ Less

Submitted 17 December, 2024; originally announced December 2024.

Counterflow and coflow instabilities in miscible binary superfluids

Authors: Yuping An, Blaise Goutéraux, Li Li

Abstract: We explore instabilities in binary superfluids with a nonvanishing relative superflow, particularly focusing on counterflow and coflow instabilities. We extend recent results on the thermodynamic origin of finite superflow instabilities in single-component superfluids to binary systems and derive a criterion for the onset of instability through a hydrodynamic analysis, which applies to interacting… ▽ More We explore instabilities in binary superfluids with a nonvanishing relative superflow, particularly focusing on counterflow and coflow instabilities. We extend recent results on the thermodynamic origin of finite superflow instabilities in single-component superfluids to binary systems and derive a criterion for the onset of instability through a hydrodynamic analysis, which applies to interacting many-body systems at finite temperature. We find that the onset of these instabilities is signaled by the determinant of the Hessian of the thermal free energy diverging and changing sign. We verify this hydrodynamic prediction in a holographic binary superfluid modeled with gauge/gravity duality, which naturally incorporates strong coupling, finite temperature, and dissipation. We also compare to results obtained using the Gross-Pitaevskii equation for weakly interacting Bose-Einstein condensates and find that the same criterion continues to apply at zero temperature, where it reduces to evaluating derivatives of the supercurrents with respect to the superfluid velocities. We observe that the critical velocities of these instabilities follow a general scaling law related to the interaction strength between superfluid components. Finally, the nonlinear stages of the instabilities are studied by full time evolution using gauge/gravity duality, where vortex annihilation leads to a decrease of superfluid velocity back to a value where the binary superfluid phase is stable. △ Less

Submitted 7 January, 2026; v1 submitted 4 November, 2024; originally announced November 2024.

Comments: Updated to published version. 42 pages, 10 figures

Quantum anomaly triggers the violation of scaling laws in gravitational system

Authors: Ya-Peng Hu, Yu-Sen An, Gao-Yong Sun, Wen-Long You, Da-Ning Shi, Hongsheng Zhang, Xiaosong Chen, Rong-Gen Cai

Abstract: Scaling laws for critical phenomena take pivotal status in almost all branches of physics. However, as scaling laws are commonly guaranteed by the renormalization group theory, systems that violate them have rarely been found. In this letter, we demonstrate that gravitational system can break scaling laws. We derive this result through investigating phase transition and critical phenomenon in a gr… ▽ More Scaling laws for critical phenomena take pivotal status in almost all branches of physics. However, as scaling laws are commonly guaranteed by the renormalization group theory, systems that violate them have rarely been found. In this letter, we demonstrate that gravitational system can break scaling laws. We derive this result through investigating phase transition and critical phenomenon in a gravitational system with quantum anomaly. For the first time, we outline the key conditions to violate the scaling laws in generic gravitational system viewed from the equation of state $P=P(T,V)$. Our results indicate that quantum effects can magnify the distinctiveness of gravity, which may be significant to understand the microscopic structure of spacetime. △ Less

Submitted 28 April, 2025; v1 submitted 31 October, 2024; originally announced October 2024.

Comments: 9 pages, 5 figures, one supplemental material added to give a physical interpretation of condition a11=0 viewed from Gibbs free energy landscape

Spin dynamics of triple-Q magnetic orderings in a triangular lattice: Implications for multi-Q orderings in general two-dimensional lattices

Authors: Pyeongjae Park, Woonghee Cho, Chaebin Kim, Yeochan An, Kazuki Iida, Ryoichi Kajimoto, Sakib Matin, Shang-Shun Zhang, Cristian D. Batista, Je-Geun Park

Abstract: Multi-Q magnetic structures on two-dimensional (2D) lattices provide a key route to realizing topological physics in 2D magnetism. A major experimental challenge is to unambiguously confirm their formation by excluding the possibility of topologically trivial multi-domain single- or double-Q magnetic orders, which cannot be distinguished using conventional diffraction techniques. Here, we propose… ▽ More Multi-Q magnetic structures on two-dimensional (2D) lattices provide a key route to realizing topological physics in 2D magnetism. A major experimental challenge is to unambiguously confirm their formation by excluding the possibility of topologically trivial multi-domain single- or double-Q magnetic orders, which cannot be distinguished using conventional diffraction techniques. Here, we propose that long-wavelength spin dynamics offers a universal diagnostic for triangular lattices: triple-Q orders that preserve rotational symmetry and single- or double-Q orders that break it exhibit qualitatively distinct anisotropies in their Goldstone mode velocities, stemming from fundamental differences in their underlying spin configurations. We validate this concept using the metallic triangular lattice antiferromagnet Co$_{0.325}$TaS$_{2}$, which hosts both a stripe-type single-Q state and a triple-Q tetrahedral ordering at different temperatures. Using inelastic neutron scattering (INS) and spin dynamics simulations, we first refine the spin Hamiltonian by fitting the paramagnetic excitation spectra, allowing us to develop an unbiased model independent of magnetic ordering. We then show that the observed velocity profiles of the Goldstone modes agree with the high-temperature model's predictions: markedly anisotropic for the single-Q phase and near isotropic for the triple-Q phase. Importantly, this contrast persists across various exchange parameters, highlighting its model-independent nature and suggesting potential applicability to other 2D lattice systems. This work provides universal insight into the dynamical properties of topological multi-Q magnetic orderings in 2D lattice structures, offering a broadly applicable diagnostic to distinguishing them from topologically trivial single- or double-Q counterparts. (For the full abstract, please refer to the manuscript) △ Less

Submitted 14 July, 2025; v1 submitted 2 October, 2024; originally announced October 2024.

Comments: 16 pages with 8 figures (plus Appendices), accepted for publication in Phys. Rev. X

Research evolution of metal organic frameworks: A scientometric approach with human-in-the-loop

Authors: Xintong Zhao, Kyle Langlois, Jacob Furst, Yuan An, Xiaohua Hu, Diego Gomez Gualdron, Fernando Uribe-Romo, Jane Greenberg

Abstract: This paper reports on a scientometric analysis bolstered by human in the loop, domain experts, to examine the field of metal organic frameworks (MOFs) research. Scientometric analyses reveal the intellectual landscape of a field. The study engaged MOF scientists in the design and review of our research workflow. MOF materials are an essential component in next generation renewable energy storage a… ▽ More This paper reports on a scientometric analysis bolstered by human in the loop, domain experts, to examine the field of metal organic frameworks (MOFs) research. Scientometric analyses reveal the intellectual landscape of a field. The study engaged MOF scientists in the design and review of our research workflow. MOF materials are an essential component in next generation renewable energy storage and biomedical technologies. The research approach demonstrates how engaging experts, via human in the loop processes, can help develop a comprehensive view of a field research trends, influential works, and specialized topics. △ Less

Submitted 16 September, 2024; originally announced September 2024.

(In)stability of symbiotic vortex-bright soliton in holographic immiscible binary superfluids

Authors: Yuping An, Li Li

Abstract: Symbiotic vortex-bright soliton structures with non-trivial topological charge in one component are found to be robust in immiscibel two-component superfluids, due to the effective potential created by a stable vortex in the other component. We explore the properties of symbiotic vortex-bright soliton in strongly coupled binary superfluids by holography, which naturally incorporates finite tempera… ▽ More Symbiotic vortex-bright soliton structures with non-trivial topological charge in one component are found to be robust in immiscibel two-component superfluids, due to the effective potential created by a stable vortex in the other component. We explore the properties of symbiotic vortex-bright soliton in strongly coupled binary superfluids by holography, which naturally incorporates finite temperature effect and dissipation. We show the dependence of the configuration on various parameters, including the winding number, temperature and inter-component coupling. We then study the (in)stability of symbiotic vortex-bright soliton by both the linear approach via quasi-normal modes and the full non-linear numerical simulation. Rich dynamics are found for the splitting patterns and dynamical transitions. Moreover, for giant symbiotic vortex-bright soliton structures with large winding numbers, the vortex splitting instability might be rooted in the Kelvin-Helmholtz instability. We also show that the second component in the vortex core could act as a stabilizer so as to suppress or even prevent vortex splitting instability. Such stabilization mechanism opens possibility for vortices with smaller winding number to merge into vortices with larger winding number, which is confirmed for the first time in our simulation. △ Less

Submitted 12 September, 2024; originally announced September 2024.

Comments: 23 pages, 10 figures

Quantum analog to flapping of flags: interface instability for co-flow binary superfluids

Authors: Yuping An, Li Li, Huabi Zeng

Abstract: We study the interface dynamics in immiscible binary superfluids using its holographic description, which naturally consists of an inviscid superfluid component and a viscous normal fluid component. We give the first theoretical realization of interface instability for two superfluid components moving with identical velocity, providing a quantum analog to the flapping of flags that is common in da… ▽ More We study the interface dynamics in immiscible binary superfluids using its holographic description, which naturally consists of an inviscid superfluid component and a viscous normal fluid component. We give the first theoretical realization of interface instability for two superfluid components moving with identical velocity, providing a quantum analog to the flapping of flags that is common in daily life. This behavior is in sharp contrast to the one from Gross-Pitaevskii equation for which no such co-flow instability develops in an isolated uniform system because of Galilean invariance. The real time evolution triggered by the dynamical instability exhibits intricate nonlinear patterns leading to quantum turbulence reminiscent of the quantum Kelvin-Helmholtz instability. Moreover, we show that such interface dynamics is essentially different from the Landau instability for which the frictionless flow becomes thermodynamically unstable above a critical superfluid velocity. Our study uncovers the rich interface dynamics of quantum fluids and the emergence of complex flow phenomena. △ Less

Submitted 19 June, 2024; originally announced June 2024.

Comments: 19 pages, 7 figures

Composition dependence of bulk properties in the Co-intercalated transition-metal dichalcogenide Co$_{1/3}$TaS$_2$

Authors: Pyeongjae Park, Woonghee Cho, Chaebin Kim, Yeochan An, Maxim Avdeev, Kazuki Iida, Ryoichi Kajimoto, Je-Geun Park

Abstract: Spontaneous Hall conductivity has recently been reported in the triangular lattice antiferromagnet Co$_{1/3}$TaS$_2$ under a zero magnetic field. This phenomenon originates from the distinctive noncoplanar triple-Q magnetic ground state, possessing uniform real-space Berry curvature characterized by scalar spin chirality. We investigated the physical properties of Co$_{1/3}$TaS$_2$ by judiciously… ▽ More Spontaneous Hall conductivity has recently been reported in the triangular lattice antiferromagnet Co$_{1/3}$TaS$_2$ under a zero magnetic field. This phenomenon originates from the distinctive noncoplanar triple-Q magnetic ground state, possessing uniform real-space Berry curvature characterized by scalar spin chirality. We investigated the physical properties of Co$_{1/3}$TaS$_2$ by judiciously controlling the composition, revealing a drastic change in its bulk properties, even by slight variations in cobalt composition, despite the same crystal structure. For $0.299 < x < 0.325$, Co$_x$TaS$_2$ keeps all the characteristics of the ground state consistent with the previous studies -- two antiferromagnetic phase transitions at $T_{N1}$ and $T_{N2} (< T_{N1})$, a large spontaneous Hall conductivity ($σ_{xy} (H=0)$), and a weak ferromagnetic moment along the c-axis. However, samples with $x > 0.330$ exhibit distinct bulk properties, including the absence of both $σ_{xy} (H=0)$ and the weak ferromagnetic moment. Our neutron diffraction data reveal that Co$_x$TaS$_2$ with $x > 0.330$ develops coplanar helical magnetic order with $q_{m1} = (1/3, 0, 0)$. This is entirely different from what has been seen in $x < 0.325$, explaining the observed composition dependence. △ Less

Submitted 18 January, 2024; originally announced January 2024.

Comments: 15 pages, 4 figures, accepted for publication in Phys. Rev. B

Journal ref: Phys. Rev. B 109, L060403 (2024)

Interface Dynamics of Strongly interacting Binary Superfluids

Authors: Yu-Ping An, Li Li, Chuan-Yin Xia, Hua-Bi Zeng

Abstract: Understanding the interface dynamics in non-equilibrium quantum systems remains a challenge. We study the interface dynamics of strongly coupled immiscible binary superfluids by using holographic duality. The full nonlinear evolution of the binary superfluids with a relative velocity shows rich nonlinear patterns toward quantum turbulence, which is reminiscent of the quantum Kelvin-Helmholtz insta… ▽ More Understanding the interface dynamics in non-equilibrium quantum systems remains a challenge. We study the interface dynamics of strongly coupled immiscible binary superfluids by using holographic duality. The full nonlinear evolution of the binary superfluids with a relative velocity shows rich nonlinear patterns toward quantum turbulence, which is reminiscent of the quantum Kelvin-Helmholtz instability. The wave number of the fast growing modes $k_0$ extracted from the interface pattern yields a non-monotonic dependence of the relative velocity, independent of the temperature and interaction. The value of $k_0$ first increases with the velocity difference and then decreases, which stands in sharp contrast to the results of mean-field theory described by the Gross-Pitaevskii equation and is confirmed by using the linear analyses on top of the stationary configuration. We uncover that the critical velocity associated with the maximum correspond to the case when the mean separation of vortices generated by interface instabilities becomes comparable to the vortex size, which could be a universal physical mechanism at strongly interacting superfluids and is directly testable in laboratory experiments. △ Less

Submitted 29 May, 2024; v1 submitted 17 January, 2024; originally announced January 2024.

Comments: Accepted version, 10 pages, 5 figures

Orientation disparity in GaN/graphene/$m$-sapphire: control-based re-examination of thru-hole epitaxy

Authors: Su Young An, Hyunkyu Lee, Gunhoon Beak, Hyeonoh Jo, Jae Hun Kim, Jongwoo Ha, Jieun Yang, Changwook Dong, Jaewu Choi, Joonwon Lim, Chinkyo Kim

Abstract: The crystallographic orientation of films grown on 2D-masked substrates is often used to infer the pathway among remote, van der Waals, and thru-hole (pinhole-seeded) epitaxy. However, attribution of a specific growth mechanism based on orientation can be ambiguous unless mask continuity and substrate pre-treatment are evaluated within a single process window. We compare GaN grown under identical… ▽ More The crystallographic orientation of films grown on 2D-masked substrates is often used to infer the pathway among remote, van der Waals, and thru-hole (pinhole-seeded) epitaxy. However, attribution of a specific growth mechanism based on orientation can be ambiguous unless mask continuity and substrate pre-treatment are evaluated within a single process window. We compare GaN grown under identical conditions on four m-plane sapphire templates: (i) bare, (ii) "graphene-grown" (high-temperature Ar/H2 with CH4 on), (iii) "anneal-only" (high-temperature Ar/H2 with CH4 off), and (iv) graphene oxide spin-coated and reduced on pristine sapphire. GaN selects (103) on graphene-grown and anneal-only m-plane sapphire, selects (100) on bare m-plane sapphire, and is predominantly (100) with a minority (103) on graphene oxide spin-coated and reduced/pristine m-plane sapphire. High-resolution TEM shows that, on partly graphene-covered samples, nucleation occurs on exposed sapphire (thru-hole), not on graphene, providing mechanism evidence independent of orientation. Within this window, the substrate surface state set by high-temperature Ar/H2 pre-treatment (rather than mask continuity) primarily governs orientation, while open-area effects can play a secondary role. Thus, preferred orientation alone may not determine the growth mechanism; mask continuity and substrate pre-treatment must be explicitly controlled when using orientation as evidence for mechanism assignment. △ Less

Submitted 20 December, 2025; v1 submitted 30 August, 2023; originally announced August 2023.

Comments: 15 pages, 5 figures

Hydrogen Transport Between Layers of Transition Metal-Dichalcogenides

Authors: Ismail Eren, Yun An, Agnieszka B. Kuc

Abstract: Hydrogen is a crucial source of green energy and has been extensively studied for its potential usage in fuel cells. The advent of two-dimensional crystals (2DCs) has taken hydrogen research to new heights, enabling it to tunnel through layers of 2DCs or be transported within voids between the layers, as demonstrated in recent experiments by Geim's group. In this study, we investigate how the comp… ▽ More Hydrogen is a crucial source of green energy and has been extensively studied for its potential usage in fuel cells. The advent of two-dimensional crystals (2DCs) has taken hydrogen research to new heights, enabling it to tunnel through layers of 2DCs or be transported within voids between the layers, as demonstrated in recent experiments by Geim's group. In this study, we investigate how the composition and stacking of transition-metal dichalcogenide (TMDC) layers influence the transport and self-diffusion coefficients (D) of hydrogen atoms using well-tempered metadynamics simulations. Our findings show that modifying either the transition metal or the chalcogen atoms significantly affects the free energy barriers (Delta F) and, consequently, the self-diffusion of hydrogen atoms between the 2DC layers. In the Hh polytype (2H stacking), MoSe2 exhibits the lowest Delta F, while WS2 has the highest, resulting in the largest D for the former system. Additionally, hydrogen atoms inside the RhM (or 3R) polytype encounter more than twice lower energy barriers and, thus, much higher diffusivity compared to those within the most stable Hh stacking. These findings are particularly significant when investigating twisted layers or homo- or heterostructures, as different stacking areas may dominate over others, potentially leading to directional transport and interesting materials for ion or atom sieving. △ Less

Submitted 7 August, 2023; originally announced August 2023.

Active learning of the thermodynamics-dynamics tradeoff in protein condensates

Authors: Yaxin An, Michael A. Webb, William M. Jacobs

Abstract: Phase-separated biomolecular condensates exhibit a wide range of dynamical properties, which depend on the sequences of the constituent proteins and RNAs. However, it is unclear to what extent condensate dynamics can be tuned without also changing the thermodynamic properties that govern phase separation. Using coarse-grained simulations of intrinsically disordered proteins, we show that the dynam… ▽ More Phase-separated biomolecular condensates exhibit a wide range of dynamical properties, which depend on the sequences of the constituent proteins and RNAs. However, it is unclear to what extent condensate dynamics can be tuned without also changing the thermodynamic properties that govern phase separation. Using coarse-grained simulations of intrinsically disordered proteins, we show that the dynamics and thermodynamics of homopolymer condensates are strongly correlated, with increased condensate stability being coincident with low mobilities and high viscosities. We then apply an "active learning" strategy to identify heteropolymer sequences that break this correlation. This data-driven approach and accompanying analysis reveal how heterogeneous amino-acid compositions and non-uniform sequence patterning map to a range of independently tunable dynamical and thermodynamic properties of biomolecular condensates. Our results highlight key molecular determinants governing the physical properties of biomolecular condensates and establish design rules for the development of stimuli-responsive biomaterials. △ Less

Submitted 9 December, 2023; v1 submitted 6 June, 2023; originally announced June 2023.

Journal ref: Science Advances 10, adj2448 2024

Higher-order topological and nodal superconducting transition-metal sulfides MS (M = Nb and Ta)

Authors: Yipeng An, Juncai Chen, Yong Yan, Jinfeng Wang, Yinong Zhou, Zhengxuan Wang, Chunlan Ma, Tianxing Wang, Ruqian Wu, Wuming Liu

Abstract: Intrinsic topological superconducting materials are exotic and vital to develop the next-generation topological superconducting devices, topological quantum calculations, and quantum information technologies. Here, we predict the topological and nodal superconductivity of MS (M = Nb and Ta) transition-metal sulfides by using the density functional theory for superconductors combining with the symm… ▽ More Intrinsic topological superconducting materials are exotic and vital to develop the next-generation topological superconducting devices, topological quantum calculations, and quantum information technologies. Here, we predict the topological and nodal superconductivity of MS (M = Nb and Ta) transition-metal sulfides by using the density functional theory for superconductors combining with the symmetry indicators. We reveal their higher-order topology nature with an index of Z4 = 2. These materials have a higher Tc than the Nb or Ta metal superconductors due to their flat-band and strong electron-phonon coupling nature. Electron doping and lighter isotopes can effectively enhance the Tc. Our findings show that the MS (M = Nb and Ta) systems can be new platforms to study exotic physics in the higher-order topological superconductors, and provide a theoretical support to utilize them as the topological superconducting devices in the field of advanced topological quantum calculations and information technologies. △ Less

Submitted 25 August, 2023; v1 submitted 6 April, 2023; originally announced April 2023.

Comments: 7 pages, 4 figures

Journal ref: Phys. Rev. B 108, 054519 (2023)

Tetrahedral triple-Q magnetic ordering and large spontaneous Hall conductivity in the metallic triangular antiferromagnet Co1/3TaS2

Authors: Pyeongjae Park, Woonghee Cho, Chaebin Kim, Yeochan An, Yoon-Gu Kang, Maxim Avdeev, Romain Sibille, Kazuki Iida, Ryoichi Kajimoto, Ki Hoon Lee, Woori Ju, En-Jin Cho, Han-Jin Noh, Myung Joon Han, Shang-Shun Zhang, Cristian D. Batista, Je-Geun Park

Abstract: The triangular lattice antiferromagnet (TLAF) has been the standard paradigm of frustrated magnetism for several decades. The most common magnetic ordering in insulating TLAFs is the 120 structure. However, a new triple-Q chiral ordering can emerge in metallic TLAFs, representing the short wavelength limit of magnetic skyrmion crystals. We report the metallic TLAF Co1/3TaS2 as the first example of… ▽ More The triangular lattice antiferromagnet (TLAF) has been the standard paradigm of frustrated magnetism for several decades. The most common magnetic ordering in insulating TLAFs is the 120 structure. However, a new triple-Q chiral ordering can emerge in metallic TLAFs, representing the short wavelength limit of magnetic skyrmion crystals. We report the metallic TLAF Co1/3TaS2 as the first example of tetrahedral triple-Q magnetic ordering with the associated topological Hall effect (non-zero σ_{xy}(H=0)). We also present a theoretical framework that describes the emergence of this magnetic ground state, which is further supported by the electronic structure measured by angle-resolved photoemission spectroscopy. Additionally, our measurements of the inelastic neutron scattering cross section are consistent with the calculated dynamical structure factor of the tetrahedral triple-Q state. △ Less

Submitted 12 November, 2023; v1 submitted 7 March, 2023; originally announced March 2023.

Comments: 23 pages, 4 figures, SI not included. Accepted for publication in Nature Communications

Journal ref: Nature Communications 14, 8346 (2023)

Quantum spin Hall insulator on the honeycomb lattice induced by ferromagnetic exchange interaction

Authors: Ye-Un An, Song-Jin O, Kwang-Il Ryom, Il-Gwang Son

Abstract: We study the many-body instabilities of correlated electrons on the half-filled honeycomb lattice with enhanced exchange coupling. The system is described by an extended Hubbard model including the next-nearest-neighbor Coulomb repulsion ($V_2$) and the nearest-neighbor exchange interaction ($J$). We use the truncated unity functional renormalization group approach to determine a schematic ground-… ▽ More We study the many-body instabilities of correlated electrons on the half-filled honeycomb lattice with enhanced exchange coupling. The system is described by an extended Hubbard model including the next-nearest-neighbor Coulomb repulsion ($V_2$) and the nearest-neighbor exchange interaction ($J$). We use the truncated unity functional renormalization group approach to determine a schematic ground-state phase diagram with higher resolution in the parameter space of $V_2$ and $J$. In the absence of the on-site repulsion and presence of sizable next-nearest-neighbor repulsion and enhanced nearest-neighbor exchange interaction, we encounter the quantum spin Hall phase, the spin-Kekulé phase, and the three-sublattice and the incommensurate charge-density-wave phases. We propose a scheme for combining consistently the truncated unity functional renormalization group and the mean-field approximation, which is distinct from the conventional one that directly uses the renormalization-group results as an input for the mean-field calculation. This scheme is used to study in detail the quantum spin Hall phase, presenting some characteristics like the bulk gap, the Chern number and the helical edge states. △ Less

Submitted 24 January, 2023; originally announced January 2023.

Comments: 17 pages, 6 figures, 1 table

Journal ref: Physica B: Condensed Matter, 655, 414748 (2023)

Two-dimensional rare-earth Janus 2$\textit{H}$-Gd$\textit{XY}$ ($\textit{X}$,$\textit{Y}$=Cl, Br, I, $\textit{X}$$\neq$$\textit{Y}$) monolayers: Bipolar ferro-magnetic semiconductors with high Curie temperature and large valley polarization

Authors: Cunquan Li, Yukai An

Abstract: Two-dimensional (2D) ferromagnetic semiconductors show great interest due to their potential applications for the nanoscale electronic devices. In this work, the Janus 2$H$-Gd$XY$ ($X$, $Y$=Cl, Br, I, $X$$\neq$$Y$) monolayers with rare-earth element Gd (4$f^{7}$+5$d^{1}$) are predicted by the first-principles calculations. Small exfoliation energy of less than 0.25 J/m$^{2}$ and excellent dynamica… ▽ More Two-dimensional (2D) ferromagnetic semiconductors show great interest due to their potential applications for the nanoscale electronic devices. In this work, the Janus 2$H$-Gd$XY$ ($X$, $Y$=Cl, Br, I, $X$$\neq$$Y$) monolayers with rare-earth element Gd (4$f^{7}$+5$d^{1}$) are predicted by the first-principles calculations. Small exfoliation energy of less than 0.25 J/m$^{2}$ and excellent dynamical/thermal stabilities can be confirmed for the Janus 2$H$-Gd$XY$ monolayers, which exhibit the bipolar magnetic semiconductor character with high Curie temperatures above 260 K and large spin-orbit coupling effect, and can be further transformed into the half-semiconductor phase under proper tensile strains (5-6\%). In addition, the in-plane magnetic anisotropy can be observed in the 2$H$-GdICl and 2$H$-GdIBr monolayers. On the contrary, the 2$H$-GdBrCl monolayer exhibits perpendicular magnetic anisotropy character, which originates from the competition between Gd-$p$/$d$ and halogen atom-$p$ orbitals. Calculated valley optical actions of the Janus 2$H$-Gd$XY$ monolayers exhibit distinguished valley-selective circular dichroisms, which is expected to realize the special valley excitation by polarized light. Spontaneously valley-Zeeman effect in the valance band for the Janus 2$H$-Gd$XY$ monolayers induces a giant valley splitting of 60-120 meV, which is also robust against various external biaxial strains. Tunable valley degree of freedom in the Janus 2$H$-Gd$XY$ systems is very necessary for encoding and processing information. △ Less

Submitted 23 March, 2023; v1 submitted 11 October, 2022; originally announced October 2022.

Comments: 8 pages, 8 figures

Two-dimensional ferromagnetic semiconductors of rare-earth Janus 2H-GdIBr monolayer with large valley polarization

Authors: Cunquan Li, Yukai An

Abstract: Based on a rare-earth Gd atom with 4$f$ electrons, through first-principles calculations, we demonstrate that the Janus 2H-GdIBr monolayer exhibits an intrinsic ferromagnetic (FM) semiconductor character with an indirect band gap of 0.75 eV, high Curie temperature T$_{c}$ of 260 K, significant magnetic moment of 8 $μ_{B}$/f.u. (f.u.=formula unit), in-plane magnetic anisotropy (IMA) and large spont… ▽ More Based on a rare-earth Gd atom with 4$f$ electrons, through first-principles calculations, we demonstrate that the Janus 2H-GdIBr monolayer exhibits an intrinsic ferromagnetic (FM) semiconductor character with an indirect band gap of 0.75 eV, high Curie temperature T$_{c}$ of 260 K, significant magnetic moment of 8 $μ_{B}$/f.u. (f.u.=formula unit), in-plane magnetic anisotropy (IMA) and large spontaneous valley polarization of 118 meV. The MAE, inter-atomic distance or angle, and T$_{c}$ can be efficiently modulated by in-plane strains and charge carrier doping. Under the strain range from $-$5% to 5% and charge carrier doping from $-$0.3e to 0.3e/f.u., the system still remains FM ordering and the corresponding T$_{c}$ can be modulated by strains from 233 K to 281 K and by charge carrier doping from 140 K to 245 K. Interestingly, under various strains, the matrix elements differences ($d_{z^{2}}$, $d_{yz}$), ($d_{x^{2}-y^{2}}$, $d_{xy}$) and ($p_{x}$, $p_{y}$) of Gd atoms dominate the MAE behaviors, which originates from the competition between the contributions of Gd-$d$, Gd-$p$ orbitals, and $p$ orbitals of halogen atoms based on the second-order perturbation theory. Inequivalent Dirac valleys are not energetic degenerate due to the time-reversal symmetry breaking in the Janus 2H-GdIBr monolayer. A considerable valley gap between the Berry curvature at the K and K$^{\prime}$ points provides an opportunity to selectively control the valley freedom and to manipulate the anomalous Hall effect. External tensile (compressive) strain further increases (decreases) the valley gap up to a maximum (minimum) value of 158 (37) meV, indicating that the valley polarization in the Janus 2H-GdIBr monolayer is robust to the external strains. △ Less

Submitted 29 August, 2022; originally announced August 2022.

Comments: 19 pages, 16 figures

Topological and nodal superconductor kagome magnesium triboride

Authors: Yipeng An, Juncai Chen, Zhengxuan Wang, Jie Li, Shijing Gong, Chunlan Ma, Tianxing Wang, Zhaoyong Jiao, Ruqian Wu, Jiangping Hu, Wuming Liu

Abstract: Recently the kagome compounds have inspired enormous interest and made some great progress such as in the field of superconductivity and topology. Here we predict a different kagome magnesium triboride (MgB3) superconductor with a calculated Tc ~12.2 K and Tc ~15.4 K by external stress, the potentially highest among the reported diverse kagome-type superconductors. We reveal its various exotic phy… ▽ More Recently the kagome compounds have inspired enormous interest and made some great progress such as in the field of superconductivity and topology. Here we predict a different kagome magnesium triboride (MgB3) superconductor with a calculated Tc ~12.2 K and Tc ~15.4 K by external stress, the potentially highest among the reported diverse kagome-type superconductors. We reveal its various exotic physical properties including the van Hove singularity, flat-band, multiple Dirac points, and nontrivial topology. The system can be described by a two-band model with highly anisotropic superconducting gaps on Fermi surfaces. Its topological and nodal superconducting nature is unveiled by a recently developed symmetry indicators method. Our results suggest that MgB3 can be a new platform to study exotic physics in the kagome structure, and pave a way to seek for more superconductors and topological materials with XY3-type kagome lattice. △ Less

Submitted 27 January, 2023; v1 submitted 25 July, 2022; originally announced July 2022.

Comments: 6 pages, 4 figures

Journal ref: Phys. Rev. Materials 7, 014205 (2023)

Controlled Curie temperature, magnetocrystalline anisotropy, and valley polarization in 2D ferromagnetic Janus 2H-VSeS monolayer

Authors: Cunquan Li, Yukai An

Abstract: Inspired by the successful synthesis of two-dimensional (2D) V-based Janus dichloride monolayers with intrinsic ferromagnetism and high Curie temperature (T$_{c}$), the electronic structure, spin-valley splitting and magnetic anisotropy of Janus 2H-VSeS monolayers are investigated in detailed using first-principles calculations. The results show that the Janus 2H-VSeS monolayer exhibits a large va… ▽ More Inspired by the successful synthesis of two-dimensional (2D) V-based Janus dichloride monolayers with intrinsic ferromagnetism and high Curie temperature (T$_{c}$), the electronic structure, spin-valley splitting and magnetic anisotropy of Janus 2H-VSeS monolayers are investigated in detailed using first-principles calculations. The results show that the Janus 2H-VSeS monolayer exhibits a large valley splitting of 105meV, high T$_{c}$ of 278K and good magnetocrystalline anisotropy (0.31meV) contributed by the in-plane d$_{x^{2}-y^{2}}$/d$_{xy}$ orbitals of V atoms. The biaxial strain ($-$8%<$\varepsilon$<8%) can effectively tune the magnetic moments of V atom, valley splitting $Δ$E, T$_{c}$ and MAE of Janus 2H-VSeS monolayer. The corresponding $Δ$E and T$_{c}$ are adjusted from 72meV to 106.8meV and from 180K to 340K, respectively. The electronic phase transition from bipolar magnetic semiconductor (BMS) to half-semiconductor (HSC), spin gapless semiconductor (SGS), and half-metal (HM) is also observed due to the change of V 3d-orbital occupation. Due to the broken space- and time-reversal symmetry, the opposite valley charge carriers carry opposite Berry curvature, which leads to prominent anomalous Hall conductivity at the K and K$^{\prime}$ valleys. The maximum modulation of Berry curvature can reach to 45% and 9.5% by applying the biaxial strain and charge carrier doping, respectively. The stable in-plane magnetocrystalline anisotropy and large spontaneous valley polarization make the ferromagnetic Janus 2H-VSeS monolayer a promising material for achieving the spintronics and valleytronics devices. △ Less

Submitted 7 July, 2022; v1 submitted 29 April, 2022; originally announced May 2022.

Comments: 13 pages, 13 figures

Nanodevices engineering and spin transport properties of MnBi2Te4 monolayer

Authors: Yipeng An, Kun Wang, Shijing Gong, Yusheng Hou, Chunlan Ma, Mingfu Zhu, Chuanxi Zhao, Tianxing Wang, Shuhong Ma, Heyan Wang, Ruqian Wu, Wuming Liu

Abstract: Two-dimensional (2D) magnetic materials are essential for the development of the next-generation spintronic technologies. Recently, layered van der Waals (vdW) compound MnBi2Te4 (MBT) has attracted great interest, and its 2D structure has been reported to host coexisting magnetism and topology. Here, we design several conceptual nanodevices based on MBT monolayer (MBT-ML) and reveal their spin-dep… ▽ More Two-dimensional (2D) magnetic materials are essential for the development of the next-generation spintronic technologies. Recently, layered van der Waals (vdW) compound MnBi2Te4 (MBT) has attracted great interest, and its 2D structure has been reported to host coexisting magnetism and topology. Here, we design several conceptual nanodevices based on MBT monolayer (MBT-ML) and reveal their spin-dependent transport properties by means of the first-principles calculations. The pn-junction diodes and sub-3-nm pin-junction field-effect transistors (FETs) show a strong rectifying effect and a spin filtering effect, with an ideality factor n close to 1 even at a reasonably high temperature. In addition, the pip- and nin-junction FETs give an interesting negative differential resistive (NDR) effect. The gate voltages can tune currents through these FETs in a large range. Furthermore, the MBT-ML has a strong response to light. Our results uncover the multifunctional nature of MBT-ML, pave the road for its applications in diverse next-generation semiconductor spin electric devices. △ Less

Submitted 11 March, 2021; originally announced March 2021.

Comments: 6 pages, 6 figures

Journal ref: npj Computational Materials, 2021

Precise phase control of large-scale inorganic perovskites via vapor-phase anion-exchange strategy

Authors: Guobiao Cen, Yufan Xia, Chuanxi Zhao, Yong Fu, Yipeng An, Ye Yuan, Tingting Shi, Wenjie Mai

Abstract: Anion exchange offers great flexibility and high precision in phase control, compositional engineering and optoelectronic property tuning. Different from previous successful anion exchange process in liquid solution, herein, we develop a vapor-phase anion-exchange strategy to realize the precise phase and bandgap control of large-scale inorganic perovskites by using gas injection cycle, produing s… ▽ More Anion exchange offers great flexibility and high precision in phase control, compositional engineering and optoelectronic property tuning. Different from previous successful anion exchange process in liquid solution, herein, we develop a vapor-phase anion-exchange strategy to realize the precise phase and bandgap control of large-scale inorganic perovskites by using gas injection cycle, produing some perovskites such as CsPbCl3 which has never been reported in thin film morphology. Ab-initio calculations also provide the insightful mechanism to understand the impact of anion exchange on tuning the electronic properties and optimizing the structural stability. Furthermore, because of precise control of specific atomic concentrations, intriguing tunable photoluminsecence is observed and photodetectors with tunable photoresponse edge from green to ultraviolet light can be realized accurately with an ultrahigh spectral resolution of 1 nm. Therefore, we offer a new, universal vapor-phase anion exchange method for inorganic perovskite with fine-tunable optoelectronic properties. △ Less

Submitted 29 September, 2020; originally announced September 2020.

Comments: 18pages,6 figures,14 FiureS,Table 1

A weak topological insulator state in quasi-one-dimensional superconductor TaSe$_3$

Authors: Jounghoon Hyun, Min Yong Jeong, Sunghun Kim, Myung-Chul Jung, Yeonghoon Lee, Chan-young Lim, Jaehun Cha, Gyubin Lee, Yeojin An, Makoto Hashimoto, Donghui Lu, Jonathan D. Denlinger, Myung Joon Han, Yeongkwan Kim

Abstract: A well-established way to find novel Majorana particles in a solid-state system is to have superconductivity arising from the topological electronic structure. To this end, the heterostructure systems that consist of normal superconductor and topological material have been actively explored in the past decade. However, a search for the single material system that simultaneously exhibits intrinsic… ▽ More A well-established way to find novel Majorana particles in a solid-state system is to have superconductivity arising from the topological electronic structure. To this end, the heterostructure systems that consist of normal superconductor and topological material have been actively explored in the past decade. However, a search for the single material system that simultaneously exhibits intrinsic superconductivity and topological phase has been largely limited, although such a system is far more favorable especially for the quantum device applications. Here, we report the electronic structure study of a quasi-one-dimensional (q1D) superconductor TaSe$_3$. Our results of angle-resolved photoemission spectroscopy (ARPES) and first-principles calculation clearly show that TaSe$_3$ is a topological superconductor. The characteristic bulk inversion gap, in-gap state and its shape of non-Dirac dispersion concurrently point to the topologically nontrivial nature of this material. The further investigations of the Z$_2$ indices and the topologically distinctive surface band crossings disclose that it belongs to the weak topological insulator (WTI) class. Hereby, TaSe$_3$ becomes the first verified example of an intrinsic 1D topological superconductor. It hopefully provides a promising platform for future applications utilizing Majorana bound states localized at the end of 1D intrinsic topological superconductors. △ Less

Submitted 13 September, 2020; originally announced September 2020.

Magnetotransport and Complexity of Holographic Metal-Insulator Transitions

Authors: Yu-Sen An, Teng Ji, Li Li

Abstract: We study the magnetotransport in a minimal holographic setup of a metal-insulator transition in two spatial dimensions. Some generic features are obtained without referring to the non-linear details of the holographic theory. The temperature dependence of resistivity is found to be well scaled with a single parameter $T_0$, which approaches zero at some critical charge density $ρ_c$, and increases… ▽ More We study the magnetotransport in a minimal holographic setup of a metal-insulator transition in two spatial dimensions. Some generic features are obtained without referring to the non-linear details of the holographic theory. The temperature dependence of resistivity is found to be well scaled with a single parameter $T_0$, which approaches zero at some critical charge density $ρ_c$, and increases as a power law $T_0\sim|ρ-ρ_c|^{1/2}$ both in metallic $(ρ>ρ_c)$ and insulating $(ρ<ρ_c)$ regions in the vicinity of the transition. Similar features also happen by changing the disorder strength as well as magnetic field. By requiring a positive definite longitudinal conductivity in the presence of an applied magnetic field restricts the allowed parameter space of theory parameters. We explicitly check the consistency of parameter range for two representative models, and compute the optical conductivities for both metallic and insulating phases, from which a disorder-induced transfer of spectral weight from low to high energies is manifest. We construct the phase diagram in terms of temperature and disorder strength. The complexity during the transition is studied and is found to be not a good probe to the metal-insulator transition. △ Less

Submitted 3 September, 2020; v1 submitted 27 July, 2020; originally announced July 2020.

Comments: 31 pages, 17 figures. v3: comments and references added, to appear in JHEP

Multifunctional Lateral Transition-Metal Disulfides Heterojunctions

Authors: Yipeng An, Yusheng Hou, Kun Wang, Shijing Gong, Chunlan Ma, Chuanxi Zhao, Tianxing Wang, Zhaoyong Jiao, Heyan Wang, Ruqian Wu

Abstract: The intrinsic spin-dependent transport properties of two types of lateral VS2|MoS2 heterojunctions are systematically investigated using first-principles calculations, and their various nanodevices with novel properties are designed. The lateral VS2|MoS2 heterojunction diodes show a perfect rectifying effect and are promising for the applications of Schottky diodes. A large spin-polarization ratio… ▽ More The intrinsic spin-dependent transport properties of two types of lateral VS2|MoS2 heterojunctions are systematically investigated using first-principles calculations, and their various nanodevices with novel properties are designed. The lateral VS2|MoS2 heterojunction diodes show a perfect rectifying effect and are promising for the applications of Schottky diodes. A large spin-polarization ratio is observed for the A-type device and pure spin-mediated current is then realized. The gate voltage significantly tunes the current and rectification ratio of their field-effect transistors (FETs). In addition, they all have sensitive photoresponse to blue light, and could be used as photodetector and photovoltaic device. Moreover, they generate the effective thermally-driven current when a temperature gratitude appears between the two terminals, suggesting them as potential thermoelectric materials. Hence, the lateral VS2|MoS2 heterojunctions show a multifunctional nature and have various potential applications in spintronics, optoelectronics, and spin caloritronics. △ Less

Submitted 1 May, 2020; originally announced May 2020.

Journal ref: Advanced Functional Materials 2020

Evaluating the exfoliation of two-dimensional materials with a Green's function surface model

Authors: Yipeng An, Yusheng Hou, Shijing Gong, Ruqian Wu, Chuanxi Zhao, Tianxing Wang, Zhaoyong Jiao, Heyan Wang, Wuming Liu

Abstract: Previous methods for the evaluation of the exfoliation of two-dimensional (2D) layered materials have drawbacks in computational efficiency and are unable to describe cases with semi-infinite substrates. Based on a Green's function surface (GFS) model, here we develop a new approach to efficiently determine the tendency of exfoliation of 2D materials from their bulk crystals or semi-infinite subst… ▽ More Previous methods for the evaluation of the exfoliation of two-dimensional (2D) layered materials have drawbacks in computational efficiency and are unable to describe cases with semi-infinite substrates. Based on a Green's function surface (GFS) model, here we develop a new approach to efficiently determine the tendency of exfoliation of 2D materials from their bulk crystals or semi-infinite substrates. By constructing appropriate surface configurations, we may calculate the exfoliation energy more precisely and quickly than the traditional way with the slab model. Furthermore, the GFS approach can provide angle-resolved photoemission spectroscopy (ARPES) of surface systems for direct comparison with experimental data. Our findings indicate that the GFS approach is powerful for studies of 2D materials and various surface problems. △ Less

Submitted 13 February, 2020; v1 submitted 9 February, 2020; originally announced February 2020.

Comments: 6 pages, 5 figures

Journal ref: Phys. Rev. B 2020

MoB2:a new multifunctional transition metal diboride monolayer

Authors: Yipeng An, Shijing Gong, Yusheng Hou, Jie Li, Ruqian Wu, Zhaoyong Jiao, Tianxing Wang, Jutao Jiao

Abstract: Several layered transition metal borides can now be realized by a simple and general fabrication method [Fokwa et al.,Adv. Mater. 2018, 30, 1704181],inspiring our interest to transition metal borides monolayer. Here, we predict a new two-dimensional (2D) transition metal diboride MoB2 monolayer (ML) and study its intrinsic mechanical, thermal, electronic, and transport properties. The MoB2 ML has… ▽ More Several layered transition metal borides can now be realized by a simple and general fabrication method [Fokwa et al.,Adv. Mater. 2018, 30, 1704181],inspiring our interest to transition metal borides monolayer. Here, we predict a new two-dimensional (2D) transition metal diboride MoB2 monolayer (ML) and study its intrinsic mechanical, thermal, electronic, and transport properties. The MoB2 ML has isotropic mechanic properties along the zigzag and armchair directions with a large Young's stiffness, and has an ultralow room-temperature thermal conductivity. The Mo atoms dominate the metallic nature of MoB2 ML. It shows an obvious electrical anisotropy and a current-limiting behavior. Our findings suggest that MoB2 ML is a promising multifunctional material used in ultrathin high-strength mechanical materials, heat insulating materials, electrical-anisotropy-based materials, and current limiters. It is helpful for the experimentalists to further prepare and utilize the transition metal diboride 2D materials. △ Less

Submitted 1 November, 2019; v1 submitted 16 October, 2019; originally announced October 2019.

Comments: 7 figures

Journal ref: J. Phys.: Condens. Matter 2020

Unveiling the Electric-current-limiting and Photodetection Effect in Two-dimensional Hydrogenated Borophene

Authors: Yipeng An, Yusheng Hou, Hui Wang, Jie Li, Ruqian Wu, Tianxing Wang, Haixia Da, Jutao Jiao

Abstract: The electronic transport and photoelectric properties of hydrogenated borophene B4H4, which was realized in a recent experiment by Nishino [J. Am. Chem. Soc. 139, 13761 (2017)], are systematically investigated using the density functional theory and non-equilibrium Green's function methods. We find that B4H4 exhibits a perfect current-limiting effect and has high (along the zigzag direction) and l… ▽ More The electronic transport and photoelectric properties of hydrogenated borophene B4H4, which was realized in a recent experiment by Nishino [J. Am. Chem. Soc. 139, 13761 (2017)], are systematically investigated using the density functional theory and non-equilibrium Green's function methods. We find that B4H4 exhibits a perfect current-limiting effect and has high (along the zigzag direction) and low (along the armchair one) optional levels due to its strong electrical anisotropy. Moreover, B4H4 can generate sizable photocurrents under illumination, with strong photoelectronic response to blue/green light along the zigzag/armchair direction. Our work demonstrates that B4H4 is promising for the applications of current limiter and photodetectors. △ Less

Submitted 14 June, 2019; v1 submitted 30 May, 2019; originally announced May 2019.

Journal ref: Phys. Rev. Appl. (2019)

Multifunctional 2D CuSe monolayer nanodevice

Authors: Yipeng An, Yusheng Hou, Hui Wang, Jie Li, Ruqian Wu, Chengyan Liu, Tianxing Wang, Jutao Jiao

Abstract: In a very recent experimental work [Gao et al., 2018 Adv. Mater. 30, 1707055], a graphene-like CuSe monolayer was realized. Motivated by this success, we performed first-principles calculations to investigate its electronic transport and photoelectronic properties. We find that the CuSe ML shows a strong electrical anisotropy, and its current-voltage (I-V) curves along the zigzag and armchair dire… ▽ More In a very recent experimental work [Gao et al., 2018 Adv. Mater. 30, 1707055], a graphene-like CuSe monolayer was realized. Motivated by this success, we performed first-principles calculations to investigate its electronic transport and photoelectronic properties. We find that the CuSe ML shows a strong electrical anisotropy, and its current-voltage (I-V) curves along the zigzag and armchair directions are noticeably different. The CuSe ML also displays a useful negative differential resistance (NDR) effect along the both directions when the bias is beyond 1.0 V. Moreover, it has a large photon absorption to orange light. Our study suggests that CuSe ML is a multifunctional material and has various potential applications in electrical-anisotropy-based, NDR-based, and even optical nanodevices. △ Less

Submitted 16 April, 2019; originally announced April 2019.

Comments: Journal of Physics: Condensed Matter 2019

Negative differential conductance effect and electrical anisotropy of 2D ZrB2 monolayers

Authors: Yipeng An, Jutao Jiao, Yusheng Hou, Hui Wang, Ruqian Wu, Chengyan Liu, Xuenian Chen, Tianxing Wang, Kun Wang

Abstract: Two-dimensional (2D) metal-diboride ZrB2 monolayers was predicted theoretically as a stable new electronic material [A. Lopez-Bezanilla, Phys. Rev. Mater., 2018, 2, 011002 (R)]. Here, we investigate its electronic transport properties along the zigzag (z-ZrB2) and armchair (a-ZrB2) directions, using the density functional theory and non-equilibrium Green's function methods. Under low biases, the 2… ▽ More Two-dimensional (2D) metal-diboride ZrB2 monolayers was predicted theoretically as a stable new electronic material [A. Lopez-Bezanilla, Phys. Rev. Mater., 2018, 2, 011002 (R)]. Here, we investigate its electronic transport properties along the zigzag (z-ZrB2) and armchair (a-ZrB2) directions, using the density functional theory and non-equilibrium Green's function methods. Under low biases, the 2D ZrB2 shows a similar electrical transport along zigzag and armchair directions as electric current propagates mostly via the metallic Zr-Zr bonds. However, it shows an electrical anistropy under high biases, and its I-V curves along zigzag and armchair directions diverge as the bias voltage is higher than 1.4 V, as more directional B-B transmission channels are opened. Importantly, both z-ZrB2 and a-ZrB2 show a pronounced negative differential conductance (NDC) effect and hence they can be promising for the use in NDC-based nanodevices. △ Less

Submitted 3 December, 2018; originally announced December 2018.

Tuning the electronic structures and transport properties of zigzag blue phosphorene nanoribbons

Authors: Yipeng An, Songqiang Sun, Mengjun Zhang, Jutao Jiao, Dapeng Wu, Tianxing Wang, Kun Wang

Abstract: In recent years, single element two-dimensional atom crystal materials have aroused extensive interest in many applications. Blue phosphorus, successfully synthesized on Au substrate by molecular beam epitaxy not long ago, shows unusual geometrical and electronic structures. We investigate the electronic structures and transport properties of zigzag blue phosphorene nanoribbons by using a first-pr… ▽ More In recent years, single element two-dimensional atom crystal materials have aroused extensive interest in many applications. Blue phosphorus, successfully synthesized on Au substrate by molecular beam epitaxy not long ago, shows unusual geometrical and electronic structures. We investigate the electronic structures and transport properties of zigzag blue phosphorene nanoribbons by using a first-principles method, which can be obviously tuned via different groups passivation on the both edges. The ZBPNRs-H and ZBPNRs-OH present a wide gap semiconductor property. While the ZBPNRs-O are metallic. Interestingly, the current-voltage curves of ZBPNRs-O show a negative differential resistive effect, which is independent on the ribbon width. The electric current through the ZBPNRs-O is mainly flowing along the both outside zigzag phosphorus chains via the way of P-P bond current. Through modifying the both edges with various functional groups, the ZBPNRs can display some important functional characteristics and become a candidate of NDR devices. △ Less

Submitted 12 October, 2018; originally announced October 2018.

Comments: IEEE Transactions On Electron Devices, 2018