Showing 1–50 of 119 results for author: Mishra, A

An Agentic Orchestration of Atomistic Simulations

Authors: Rahul Somasundaram, Adela Habib, Khanh Dang, Sachin Shivakumar, Ryley G. Hill, Golo Wimmer, Avanish Mishra, Aleksandra Pachalieva, Arthur Lui, Hari Viswanathan, Michael Grosskopf, Saryu Fensin, Russell Bent, Nathan DeBardeleben, Earl Lawrence

Abstract: Atomistic simulations are central to materials design, but their execution involves complex, multi-step workflows that require significant human expertise. Here, we present an agent-based system embedded within the URSA (Universal Research and Scientific Agent) framework that automates the design, execution, and validation of atomistic simulations, demonstrated using the Large-scale Atomic/Molecul… ▽ More Atomistic simulations are central to materials design, but their execution involves complex, multi-step workflows that require significant human expertise. Here, we present an agent-based system embedded within the URSA (Universal Research and Scientific Agent) framework that automates the design, execution, and validation of atomistic simulations, demonstrated using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) tool. Our system autonomously selects interatomic potentials, constructs and runs simulations, and performs iterative error recovery within a closed-loop workflow. We evaluate the scientific reliability of the agent by benchmarking its outputs against LAVA, a high-throughput toolkit for LAMMPS and the Vienna Ab initio Simulation Package (VASP) calculations. Our framework reduces manual intervention and trial-and-error, thereby improving the rigor, reproducibility, and scalability of atomistic modeling. △ Less

Submitted 11 June, 2026; originally announced July 2026.

Comments: 19 pages, 9 figures

Report number: LA-UR-26-24722

Interface-resolved structural properties of epitaxial Y$_3$Fe$_5$O$_{12}$/ Gd$_3$Fe$_5$O$_{12}$ bilayers grown on GGG(111) by pulsed laser deposition

Authors: Kshitij Singh Rathore, Abhisek Mishra, Swayang Priya Mahanta, Shubhransu Sahoo, Anupama Swain, Pushpendra Gupta, Kapil Gupta, Jose M. Caicedo-Roque, Jessica Padilla-Pantoja, Francisco J. Belarre, Belen Ballesteros, Jose Santiso, Subhankar Bedanta

Abstract: Epitaxial Y$_3$Fe$_5$O$_{12}$ (YIG) and Gd$_3$Fe$_5$O$_{12}$ (GdIG) thin films, along with their bilayer heterostructures, were grown on Gd$_3$Ga$_5$O$_{12}$(GGG)(111) substrates using pulsed laser deposition. Structural properties were investigated using X-ray diffraction, reciprocal space mapping, and cross-sectional transmission electron microscopy. The results confirm high crystalline quality… ▽ More Epitaxial Y$_3$Fe$_5$O$_{12}$ (YIG) and Gd$_3$Fe$_5$O$_{12}$ (GdIG) thin films, along with their bilayer heterostructures, were grown on Gd$_3$Ga$_5$O$_{12}$(GGG)(111) substrates using pulsed laser deposition. Structural properties were investigated using X-ray diffraction, reciprocal space mapping, and cross-sectional transmission electron microscopy. The results confirm high crystalline quality and coherent epitaxial growth, with RSM revealing a coexistence of strained and partially relaxed regions governed by layer sequence. TEM analysis shows sharp interfaces, columnar microstructures, and antiphase boundaries that facilitate strain relaxation. A comparative study indicates that the GGG/YIG/GdIG stacking sequence exhibits improved structural quality with reduced defect density, attributed to the superior epitaxial growth of YIG on the substrate. These findings highlight the critical role of growth sequence in controlling strain and interfacial structure in garnet heterostructures. △ Less

Submitted 22 July, 2026; originally announced July 2026.

Benchmarking the Dual Fermion approach on the Falicov-Kimball model

Authors: Akshat Mishra, Hugo U. R. Strand, Erik G. C. P. van Loon

Abstract: Strong electronic correlations generally require non-perturbative treatment. Local correlations are captured by dynamical mean-field theory while nonlocal correlations can be treated with diagrammatic extensions such as the Dual Fermion approach. Dual Fermion is built on physically motivated, but in principle uncontrolled approximations, so careful benchmarking is needed to understand the strength… ▽ More Strong electronic correlations generally require non-perturbative treatment. Local correlations are captured by dynamical mean-field theory while nonlocal correlations can be treated with diagrammatic extensions such as the Dual Fermion approach. Dual Fermion is built on physically motivated, but in principle uncontrolled approximations, so careful benchmarking is needed to understand the strengths and limitations of the method. In this work, we benchmark ladder Dual Fermion and dynamical mean-field theory for the Falicov-Kimball model with the exact classical Monte Carlo solution. We focus on the thermodynamics, electronic structure and susceptibility, especially at the combined frequency and momentum structure, and find that Dual Fermion clearly outperforms dynamical mean-field theory. Somewhat surprisingly, Dual Fermion is not as accurate for the relation between orbital density versus chemical potential in the doped system. These results demonstrate the need for rigorous benchmarking of diagrammatic extensions of dynamical mean-field theory for models with inequivalent orbitals, which is essential for modelling materials. △ Less

Submitted 4 May, 2026; originally announced May 2026.

A Top-Loading Point-Contact Spectroscopy Probe with In-Situ Sample Exchange for Dilution Refrigerators

Authors: Ghulam Mohmad, Atanu Mishra, Goutam Sheet

Abstract: We report the design and implementation of a point-contact spectroscopy (PCS) system integrated with a dilution refrigerator, enabling measurements down to 30 mK. The setup employs a needle-anvil geometry with a cryogenic piezo-driven nanopositioner for in-situ formation of mesoscopic point contacts. We discuss the thermal anchoring strategies that enable efficient cooling of the probe to ultra-lo… ▽ More We report the design and implementation of a point-contact spectroscopy (PCS) system integrated with a dilution refrigerator, enabling measurements down to 30 mK. The setup employs a needle-anvil geometry with a cryogenic piezo-driven nanopositioner for in-situ formation of mesoscopic point contacts. We discuss the thermal anchoring strategies that enable efficient cooling of the probe to ultra-low temperatures and reliable measurements. We also address positioner-related challenges and the solutions implemented to ensure stable operation at millikelvin temperatures. The performance of the probe is demonstrated through point contact spectroscopy on Ta-doped TiSe$_2$ (Ta$_x$Ti$_{1-x}$Se$_2$, $x = 0.2$), a superconductor with $T_c \approx 2.3$ K. The spectra exhibit well-defined superconducting features that systematically diminish with increasing temperature and magnetic field. The platform provides a robust and versatile tool for spectroscopic investigations of superconductors and other quantum materials at millikelvin temperatures and high magnetic fields. △ Less

Submitted 4 April, 2026; originally announced April 2026.

Comments: 9pages ,6 figures

Geometric and Topological Deep Learning for Predicting Thermo-mechanical Performance in Cold Spray Deposition Process Modeling

Authors: Akshansh Mishra

Abstract: This study presents a geometric deep learning framework for predicting cold spray particle impact responses using finite element simulation data. A parametric dataset was generated through automated Abaqus simulations spanning a systematic range of particle velocity, particle temperature, and friction coefficient, yielding five output targets including maximum equivalent plastic strain, average co… ▽ More This study presents a geometric deep learning framework for predicting cold spray particle impact responses using finite element simulation data. A parametric dataset was generated through automated Abaqus simulations spanning a systematic range of particle velocity, particle temperature, and friction coefficient, yielding five output targets including maximum equivalent plastic strain, average contact plastic strain, maximum temperature, maximum von Mises stress, and deformation ratio. Four novel algorithms i.e. a GraphSAGE-style inductive graph neural network, a Chebyshev spectral graph convolution network, a topological data analysis augmented multilayer perceptron, and a geometric attention network were implemented and evaluated. Each input sample was treated as a node in a k-nearest-neighbour feature-space graph, enabling the models to exploit spatial similarity between process conditions during training. Three-dimensional feature space visualisations and two-dimensional contour projections confirmed the highly non-linear and velocity-dominated nature of the input-output relationships. Quantitative evaluation demonstrated that GraphSAGE and GAT consistently achieved R-square values exceeding 0.93 across most targets, with GAT attaining peak performance of R-square equal to 0.97 for maximum plastic strain. ChebSpectral and TDA-MLP performed considerably worse, yielding negative R-square values for several targets. These findings establish spatial graph-based neighbourhood aggregation as a robust and physically interpretable surrogate modelling strategy for cold spray process optimisation. △ Less

Submitted 15 March, 2026; originally announced March 2026.

Comments: 27 pages, 19 figures, 6 tables

Nitrogen-Vacancy-Mediated Magnetism in Sputtered GdN Thin Films

Authors: Pankaj Bhardwaj, Jyotirmoy Sarkar, Bubun Biswal, Subhransu Kumar Negi, Arijit Sinha, Anirudh Venugopalrao, Sharath Kumar C, Sreelakshmi M Nair, R. S. Patel, Deepshika Jaiswal Nagar, Abhishek Mishra, Srinivasan Raghavan, Umesh Waghmare, Dhavala Suri

Abstract: Among rare-earth nitrides (RENs), gadolinium nitride (GdN) stands out as a promising material for spintronics owing to its distinctive combination of semiconducting behavior, strong exchange interactions, and intrinsically soft ferromagnetism. Its relatively high Curie temperature and large saturation magnetization make it an attractive candidate for device concepts such as non-volatile memory ele… ▽ More Among rare-earth nitrides (RENs), gadolinium nitride (GdN) stands out as a promising material for spintronics owing to its distinctive combination of semiconducting behavior, strong exchange interactions, and intrinsically soft ferromagnetism. Its relatively high Curie temperature and large saturation magnetization make it an attractive candidate for device concepts such as non-volatile memory elements and spin-based transistors, motivating efforts toward low-cost, uniform, and compositionally controlled thin-film growth. In this work, we deposited GdN thin films on SiO2/AlN substrates using DC sputtering under reactive nitridation conditions, with thicknesses varying from 18 to 180 nm, and systematically investigated their structural and magnetic properties. The films exhibit soft ferromagnetic ordering, characterized by a coercive field of approximately 200 Oe and a Curie temperature (Tc) near 70 K. Structural analysis reveals lattice distortions and local strain associated with nitrogen-vacancy defects, whose concentration varies with film thickness. Our theoretical studies establish a direct correlation between the observed Raman modes of the GdN lattice and the reduced magnetization induced by nitrogen vacancies. These vacancies give rise to defect-mediated ferromagnetism, leading to a measurable enhancement of Tc from 68 K to 82 K across the studied thickness range. The observed magnetic behavior is well described by the bound magnetic polaron (BMP) model, confirming that nitrogen vacancies are key contributors to ferromagnetic ordering while preserving the soft-magnetic character intrinsic to GdN. This study underscores the pivotal role of defect engineering in optimizing GdN thin films for spintronics applications. △ Less

Submitted 14 March, 2026; originally announced March 2026.

Report number: Volume 59, Number 31

Journal ref: Journal of Physics D: Applied Physics,2026

Machine Learning for Electrode Materials: Property Prediction via Composition

Authors: Hao Wu, Cameron Hargreaves, Arpit Mishra, Gian-Marco Rignanese

Abstract: In this work, we benchmark three leading composition based Machine Learning (ML) frameworks, MODNet, CrabNet, and a random forest model based on Magpie features, predicting the properties of battery electrode materials using the Materials Project Battery Explorer dataset. We evaluate these models based on predictive accuracy, visualize numerical features using two-dimensional embeddings, and quant… ▽ More In this work, we benchmark three leading composition based Machine Learning (ML) frameworks, MODNet, CrabNet, and a random forest model based on Magpie features, predicting the properties of battery electrode materials using the Materials Project Battery Explorer dataset. We evaluate these models based on predictive accuracy, visualize numerical features using two-dimensional embeddings, and quantify performance using standard metrics. Our results demonstrate that CrabNet consistently outperforms the other models across all tests. To validate these findings, we employ bootstrap resampling and two cross-validation (CV) strategies (leave-one-cluster-out and stratified 5-fold CV), comparing each model against a control baseline, using unseen experimental data as a hold-out test. We also apply unsupervised clustering using t-SNE and DBSCAN on physically observed features extracted from matminer, revealing coherent material groupings without prior labels. The final selected model consistently improves over controls, and we believe can be used as a early stage oracle for electrode materials composition screening. Our study aims to identify the error distributions and limitations of the approach, discussing the challenges with developing robust ML models. Despite these constraints, our findings suggest the final selected model is effective for early-stage compositional screening. △ Less

Submitted 17 July, 2026; v1 submitted 8 March, 2026; originally announced March 2026.

Comments: 34 pages, 13 figures

Origin of mixed anisotropy in crystalline Permalloy and amorphous Cobalt thin films individually deposited on Si substrate

Authors: Kirti Kirti, Baisali Ghadai, Abinash Mishra, Rahulkrishnan R, Sucheta Mondal

Abstract: Magnetic anisotropy (MA) plays a crucial role in deciding both static and dynamic behaviour of magnetic thin films. It controls various phenomena, such as magnetization reversal, domain formation, domain-wall motion, spin-wave generation, and spin-wave propagation etc. We investigate the mixed anisotropies in face-centred-cubic Permalloy (fcc-Py) and amorphous Cobalt (a-Co) thin films deposited vi… ▽ More Magnetic anisotropy (MA) plays a crucial role in deciding both static and dynamic behaviour of magnetic thin films. It controls various phenomena, such as magnetization reversal, domain formation, domain-wall motion, spin-wave generation, and spin-wave propagation etc. We investigate the mixed anisotropies in face-centred-cubic Permalloy (fcc-Py) and amorphous Cobalt (a-Co) thin films deposited via rf magnetron sputtering on Si (100) substrate with thicknesses, d = 5-125 nm and t = 5-150 nm, respectively. X-ray diffraction technique, atomic force microscopy, and vibrating sample magnetometry are employed to study the structural, morphological, and magnetic properties. We adopt a qualitative approach to understand the nature of different anisotropies present in both materials. Mixed anisotropies evolve with film thicknesses for both fcc-Py and a-Co films. The role of growth conditions in the emergence of specific anisotropies is discussed in detail. An alteration of the magnetization easy axis from the conventional in-plane orientation is evidenced due to the collective influence of these mixed anisotropies. Based on the dominance of anisotropy components, their origin, and the direction of magnetization tilt, we categorize our samples as belonging to specific regimes. Introduction of magnetization tilt has been proven to be an extremely innovative way to improve the performance of spintronic devices so far. The one-to-one comparison between a sputter-deposited crystalline and an amorphous magnetic material could be beneficial for building a stronger foundation for that. △ Less

Submitted 3 February, 2026; originally announced February 2026.

Universality of Type-II Multiferroicity in Monolayer Nickel Dihalides

Authors: Aleš Cahlík, Antti Karjasilta, Anshika Mishra, Robert Drost, Mohammad Amini, Javaria Arshad, Büşra Arslan, Peter Liljeroth

Abstract: The recent discovery of type-II multiferroicity in monolayer NiI${_2}$ indicated a new pathway for intrinsic magnetoelectric coupling in the two-dimensional limit. However, determining whether this phenomenon is a unique anomaly or a general, chemically tunable property of the material class remains unresolved. Here, we demonstrate the universality of type-II multiferroicity in the transition meta… ▽ More The recent discovery of type-II multiferroicity in monolayer NiI${_2}$ indicated a new pathway for intrinsic magnetoelectric coupling in the two-dimensional limit. However, determining whether this phenomenon is a unique anomaly or a general, chemically tunable property of the material class remains unresolved. Here, we demonstrate the universality of type-II multiferroicity in the transition metal dihalides by visualizing the ferroelectric order in monolayer NiBr${_2}$. Using scanning tunneling microscopy (STM), we resolve atomic-scale ferroelectric domains and confirm their magnetoelectric origin through reciprocal manipulation experiments: reorienting magnetic order via electric fields and suppressing the electric polarization with external magnetic fields. Furthermore, we find that the multiferroic state in NiBr${_2}$ is energetically less robust than in its iodide counterpart, consistent with modified superexchange interactions and the reduced spin-orbit coupling. Our results establish the transition metal dihalides as a versatile platform where the stability of magnetoelectric phases can be engineered through chemical substitution. △ Less

Submitted 28 January, 2026; originally announced January 2026.

Magnetic field decouples nodeless surface and nodal bulk orders in PdTe

Authors: Atanu Mishra, Ghulam Mohmad, Kiran Bansal, Mohd Monish, Pankaj Kumar, Chandrasekhar Yadav, Goutam Sheet

Abstract: Selective spectroscopic disentanglement of surface and bulk quantum orders remains an outstanding challenge in condensed matter physics. The candidate topological superconductor PdTe has recently been proposed to host a nodeless surface gap on top of a nodal bulk state, but their direct identification and mutual coupling remained experimentally elusive. Here, we employ magnetic-field-dependent And… ▽ More Selective spectroscopic disentanglement of surface and bulk quantum orders remains an outstanding challenge in condensed matter physics. The candidate topological superconductor PdTe has recently been proposed to host a nodeless surface gap on top of a nodal bulk state, but their direct identification and mutual coupling remained experimentally elusive. Here, we employ magnetic-field-dependent Andreev reflection spectroscopy to spectroscopically disentangle these components. At zero magnetic field, the spectra exhibit a BCS-like gap structure, consistent with dominant transport through a fully gapped surface superconducting state. Strikingly, even a weak magnetic field leads to an abrupt suppression of the Andreev-enhanced conductance (AEC), while a residual AEC, attributable to the nodal bulk state, persists to much higher magnetic fields. The transition is accompanied by pronounced magnetic hysteresis pointing to the existence of vortex dynamics at low fields. Our findings suggest that the nodal bulk gap facilitates early vortex entry, which in turn disrupts the fragile surface superconductivity. These results establish a field-tunable decoupling of surface and bulk superconductivity and illustrate how distinct gap topologies can shape the global superconducting order in multichannel systems. △ Less

Submitted 13 January, 2026; v1 submitted 12 January, 2026; originally announced January 2026.

Selective Amplification of the Topological Hall Signal in Cr$_2$Te$_3$: The Role of Molecular Exchange Coupling

Authors: Suman Mundlia, Ritesh Kumar, Anshika Mishra, Malavika Chandrasekhar, Narayan Mohanta, Karthik V. Raman

Abstract: Layered magnetic transition-metal chalcogenides (TMCs) are a focal point of research, revealing a variety of intriguing magnetic and topological ground states. Within this family of TMCs, chromium telluride has garnered significant attention because of its excellent tunability in magnetic response, owing to the presence of competing magnetic exchange interactions. We here demonstrate the manipulat… ▽ More Layered magnetic transition-metal chalcogenides (TMCs) are a focal point of research, revealing a variety of intriguing magnetic and topological ground states. Within this family of TMCs, chromium telluride has garnered significant attention because of its excellent tunability in magnetic response, owing to the presence of competing magnetic exchange interactions. We here demonstrate the manipulation of magnetic anisotropy in ultra-thin Cr$_2$Te$_3$ films through growth engineering leading to a controlled transition from in-plane to out-of-plane orientation with an intermediate non-coplanar magnetic ground phase characterized by a topological Hall effect. Moreover, interfacing these films with Vanadyl phthalocyanine (VOPc) molecules prominently enhances the non-coplanar magnetic phase, attributing its presence to the competing interfacial magnetic exchange interactions over the spin-orbit-driven interfacial effects. These findings pave the way for the realization of novel topological spintronic devices through interface-modulated exchange coupling. △ Less

Submitted 30 December, 2025; originally announced December 2025.

Atomistic Simulation Guided Convolutional Neural Networks for Thermal Modeling of Friction Stir Welding

Authors: Akshansh Mishra

Abstract: Accurate prediction of temperature evolution is essential for understanding thermomechanical behavior in friction stir welding. In this study, molecular dynamics simulations were performed using LAMMPS to model aluminum friction stir welding at the atomic scale, capturing material flow, plastic deformation, and heat generation during tool plunge, traverse, and retraction. Atomic positions and velo… ▽ More Accurate prediction of temperature evolution is essential for understanding thermomechanical behavior in friction stir welding. In this study, molecular dynamics simulations were performed using LAMMPS to model aluminum friction stir welding at the atomic scale, capturing material flow, plastic deformation, and heat generation during tool plunge, traverse, and retraction. Atomic positions and velocities were extracted from simulation trajectories and transformed into physics based two dimensional spatial grids. These grids represent local height variation, velocity components, velocity magnitude, and atomic density, preserving spatial correlations within the weld zone. A two-dimensional convolutional neural network was developed to predict temperature directly from the spatially resolved atomistic data. Hyperparameter optimization was carried out to determine an appropriate network configuration. The trained model demonstrates strong predictive capability, achieving a coefficient of determination R square of 0.9439, a root mean square error of 14.94 K, and a mean absolute error of 11.58 K on unseen test data. Class Activation Map analysis indicates that the model assigns higher importance to regions near the tool material interface, which are associated with intense deformation and heat generation in the molecular dynamics simulations. The results show that spatial learning from atomistic simulation data can accurately reproduce temperature trends in friction stir welding while remaining consistent with physical deformation and flow mechanisms observed at the atomic scale. △ Less

Submitted 15 December, 2025; originally announced December 2025.

Comments: 25 pages, 11 figures, 2 tables

Anomalous Hysteresis Behavior in Sputter-deposited Ultrathin Films of Amorphous- CoFeB Alloy

Authors: Baisali Ghadai, Kirti Kirti, Abinash Mishra, Sucheta Mondal

Abstract: Thin amorphous-CoFeB (a-CFB) is deposited by rf-magnetron sputtering on a self-oxidized Si (100) substrate with different film thicknesses ranging from 0.7 nm to 20 nm. The 5-nm-thick a-CFB film is capped with a W layer for comparison. The surface morphology is investigated by using the atomic force microscopy technique. The low roughness of all the surface of the film indicates uniformity, modera… ▽ More Thin amorphous-CoFeB (a-CFB) is deposited by rf-magnetron sputtering on a self-oxidized Si (100) substrate with different film thicknesses ranging from 0.7 nm to 20 nm. The 5-nm-thick a-CFB film is capped with a W layer for comparison. The surface morphology is investigated by using the atomic force microscopy technique. The low roughness of all the surface of the film indicates uniformity, moderate corrosion resistance, and good structural quality. The X-ray diffraction spectra reveal the amorphous nature of the CFB layer, while the W capping is of mixed phase in the experimental thickness regime. In-plane and out-of-plane hysteresis loops obtained from the vibrating sample magnetometry technique show a transition from an upright S to nearly rectangular shape via a completely inverted profile. A self-sustained tilted magnetic anisotropy is stabilized in a seed-free environment based on the direct substrate-to-magnet interaction. The interface anisotropy is estimated to be 0.06 erg/cm2. The complex anisotropic behavior originates from the interplay between interface anisotropy, conventional shape anisotropy, growth-induced anisotropies, and inhomogeneity-induced anisotropies. In essence, effective anisotropy is responsible for the anomalous hysteresis behavior observed in these films, and this work might provide valuable insights to improve the functionalities of amorphous soft magnetic alloys. △ Less

Submitted 20 December, 2025; originally announced December 2025.

Deep Learning Enabled Nanoscale X-ray Photoemission Electron Microscopy (nanoXPEEM)

Authors: Aashwin Mishra, Daniel Ratner, Quynh Nguyen

Abstract: Understanding and manipulating two-dimensional materials for real-world applications remains challenging due to a lack of effective and high-throughput characterization techniques. Soft X-ray time-of-flight photoemission electron microscopy (XPEEM) provides element- and depth-sensitive information of materials and buried interfaces. However, chromatic and spherical aberrations cannot be corrected… ▽ More Understanding and manipulating two-dimensional materials for real-world applications remains challenging due to a lack of effective and high-throughput characterization techniques. Soft X-ray time-of-flight photoemission electron microscopy (XPEEM) provides element- and depth-sensitive information of materials and buried interfaces. However, chromatic and spherical aberrations cannot be corrected with electron-lens combinations. These aberrations, combined with astigmatism and space-charge effects, significantly degrade the spatial and energy resolutions. To overcome this limitation, we outline a spatial-attention based deep learning approach to automatically correct for these effects and attain nanometer resolution over the entire field-of-view (FoV). The combination of this corrective algorithm with XPEEM, termed as nanoXPEEM, establishes a new record of 48-nm spatial resolution with a 232-micrometer diameter FoV in the soft x-ray regime (700-1000 eV). nanoXPEEM provides unique spatial mapping of the element-specificity, depth-sensitivity, and local structure on the nanoscale. It can bridge the current gap to achieve angstrom (atomic) scale resolution. △ Less

Submitted 19 December, 2025; originally announced December 2025.

Robust Superconductivity and High Upper Critical Fields in Epitaxial cubic W2N Thin Films

Authors: Aditya Singh, Arnaud le Febvrier, Sanath Kumar Honnali, Abhisek Mishra, Grzegorz Greczynski, Subhankar Bedanta, Per Eklund, Ajay Soni

Abstract: Transition Metal Nitrides are a versatile class of materials, combining chemical robustness, high hardness, and superconducting behaviour with critical temperatures between 2 to 10 K. While several binary TMNs have been explored, superconductivity in stoichiometric W2N has remained largely unexplored. Here, we report on superconducting thin films of stoichiometric W2N, demonstrating a distinctly h… ▽ More Transition Metal Nitrides are a versatile class of materials, combining chemical robustness, high hardness, and superconducting behaviour with critical temperatures between 2 to 10 K. While several binary TMNs have been explored, superconductivity in stoichiometric W2N has remained largely unexplored. Here, we report on superconducting thin films of stoichiometric W2N, demonstrating a distinctly high upper critical field of 8.5 T, uncommon among binary TMNs. This robust superconducting response under high magnetic fields highlights the technological relevance of W2N for integrated quantum and cryogenic electronic platforms. Overall, these results position stoichiometric W2N as a promising addition to the TMN superconducting landscape, opening new avenues for functional materials design based on chemically stable and mechanically resilient nitrides. △ Less

Submitted 6 December, 2025; originally announced December 2025.

Comments: 13 page 4 figure

A Linear-Scaling, Charge-Aware Foundation Potential for Atomistic Simulations

Authors: Tsz Wai Ko, Runze Liu, Adesh Rohan Mishra, Zihan Yu, Ji Qi, Shyue Ping Ong

Abstract: Electrostatics govern charge transfer and reactivity in materials. However, most foundation potentials (FPs) either neglect explicit electrostatic interactions or come at prohibitive computational cost. Here, we introduce charge-equilibrated TensorNet (QET), an equivariant, charge-aware architecture that achieves linear scaling with system size via an analytically solvable charge-equilibration sch… ▽ More Electrostatics govern charge transfer and reactivity in materials. However, most foundation potentials (FPs) either neglect explicit electrostatic interactions or come at prohibitive computational cost. Here, we introduce charge-equilibrated TensorNet (QET), an equivariant, charge-aware architecture that achieves linear scaling with system size via an analytically solvable charge-equilibration scheme. We demonstrate that a trained QET FP matches state-of-the-art FPs on materials property benchmarks but delivers qualitatively different predictions in systems dominated by electrostatic interactions. The QET FP reproduces the correct structure and density of the NaCl-CaCl2 ionic liquid and the crystallization of Ge1Sb2Te4 phase change memory, which charge-agnostic FPs miss. We further show that a fine-tuned QET captures reactive processes at the Li/Li6PS5Cl solid-electrolyte interface and supports simulations under applied electrochemical potentials. These results remove a fundamental constraint in large-scale atomistic simulations of electrostatics and establish a general, data-driven framework for charge-aware FPs with transformative applications in energy storage, catalysis, and beyond. △ Less

Submitted 15 August, 2026; v1 submitted 10 November, 2025; originally announced November 2025.

Comments: 63 pages (43 for Manuscript + 20 for SI), 21 figures (5 for Manuscript + 16 for SI)

Pressure-Driven Phase Evolution and Optoelectronic Properties of Lead-free Halide Perovskite Rb$_2$TeBr$_6$

Authors: Suvashree Mukherjee, Asish Kumar Mishra, K. A. Irshad, Boby Joseph, Goutam Dev Mukherjee

Abstract: The structural, vibrational, and optical properties of Rb$_2$TeBr$_6$ have been investigated under high pressure using synchrotron X-ray diffraction, Raman spectroscopy, photoluminescence (PL), and optical absorption measurements. At ambient conditions, Rb$_2$TeBr$_6$ crystallizes in the cubic Fm-3m structure, which remains stable below 8.0 GPa. Within this pressure range, subtle inter-octahedral… ▽ More The structural, vibrational, and optical properties of Rb$_2$TeBr$_6$ have been investigated under high pressure using synchrotron X-ray diffraction, Raman spectroscopy, photoluminescence (PL), and optical absorption measurements. At ambient conditions, Rb$_2$TeBr$_6$ crystallizes in the cubic Fm-3m structure, which remains stable below 8.0 GPa. Within this pressure range, subtle inter-octahedral rotations develop, producing a gradual localized deviation from the ideal cubic framework. This local reorientation facilitates radiative recombination, leading to a pronounced enhancement of PL intensity with pressure up to 2.4 GPa. Beyond this pressure point, enhancement of nonradiative relaxation channels result in gradual PL quenching. Additionally, the PL intensity increases upon the application of an external weak magnetic field. A structural transition to the orthorhombic Pnnm phase occurs at around 8.0 GPa, followed by a monoclinic P$2_1/m$ phase above 10.7 GPa, and eventual amorphization beyond 25.5 GPa. Optical absorption spectra reveal continuous band-gap narrowing upon compression. These findings demonstrate the strong coupling among lattice dynamics, electronic structure, and optical response in Rb$_2$TeBr$_6$, underscoring its potential as a pressure-tunable optoelectronic material △ Less

Submitted 17 April, 2026; v1 submitted 4 November, 2025; originally announced November 2025.

Morphotropic Phase Boundary (MPB) Induced Enhancement of Ferroelectric and Piezoelectric Properties in Li and Ta modified K0.5Na0.5NbO3

Authors: Satyaranjan Sahoo, Dhiren K. Pradhan, Shalini Kumari, Abhisikta Sahu, Koyal Suman Samantaray, Vikas N. Thakur, Anupam Mishra, M. M. Rahaman, Ashok Kumar, Reji Thomas, Philip D. Rack, Dillip K. Pradhan

Abstract: Lead-free (K0.48Na0.48Li0.04)(Nb1-xTax)O3 (KNLNT-x) ceramics were synthesized to study the effects of Li and Ta substitution on phase transition behavior, microstructure, and ferroelectric, dielectric, and piezoelectric properties. X-ray diffraction and Raman spectroscopy show that compositions with x < 0.10 exhibit a single orthorhombic (Amm2) phase, while 0.10 <= x <= 0.20 show coexistence of or… ▽ More Lead-free (K0.48Na0.48Li0.04)(Nb1-xTax)O3 (KNLNT-x) ceramics were synthesized to study the effects of Li and Ta substitution on phase transition behavior, microstructure, and ferroelectric, dielectric, and piezoelectric properties. X-ray diffraction and Raman spectroscopy show that compositions with x < 0.10 exhibit a single orthorhombic (Amm2) phase, while 0.10 <= x <= 0.20 show coexistence of orthorhombic and tetragonal (Amm2 + P4mm) phases. For x > 0.20, a single tetragonal (P4mm) phase is obtained. Microstructural analysis shows a dense ceramic with decreasing grain size as Ta concentration increases. Temperature-dependent dielectric studies reveal two transitions: orthorhombic-tetragonal (TO-T) and tetragonal-cubic (TC). Both transition temperatures decrease systematically with increasing Ta, and TO-T shifts below room temperature for x > 0.15. The composition KNLNT-0.20 exhibits the highest dielectric constant (Er = 556) and piezoelectric coefficient (d33 = 159 pC/N). The enhanced piezoelectric response is attributed to a morphotropic phase boundary rather than a shift of the polymorphic phase boundary temperature. A composition-temperature phase diagram was constructed based on XRD, Raman, and dielectric data. △ Less

Submitted 16 October, 2025; originally announced October 2025.

Comments: 45 Pages, 7 main Figures

InSpecLearn4SDL: Interpretable Spectral Features Predict Conductivity in Self-Driving Doped Conjugated Polymer Labs

Authors: Ankush Kumar Mishra, Jacob P. Mauthe, Nicholas Luke, Aram Amassian, Baskar Ganapathysubramanian

Abstract: To accelerate materials discovery using self-driving labs (SDLs), we present a machine learning pipeline that predicts the electrical conductivity of doped conjugated polymers using rapid, non-destructive optical spectroscopy. Our approach automates spectral featurization by combining a genetic algorithm with adaptive area-under-the-curve (AUC) computations, creating a quantitative structure-prope… ▽ More To accelerate materials discovery using self-driving labs (SDLs), we present a machine learning pipeline that predicts the electrical conductivity of doped conjugated polymers using rapid, non-destructive optical spectroscopy. Our approach automates spectral featurization by combining a genetic algorithm with adaptive area-under-the-curve (AUC) computations, creating a quantitative structure-property relationship (QSPR) that links optical response and processing parameters to conductivity. By incorporating SHAP-guided selection and domain-knowledge-based feature expansion, the model matches expert-curated performance while theoretically reducing experimental effort by $\sim 33\%$ by minimizing the need for costly direct conductivity measurements. Notably, the model recovers known physical descriptors in pBTTT and identifies informative tail-state regions correlated with polymer bleaching upon successful doping. This generic, interpretable, small-data-friendly methodology can be extended to other spectroscopic modalities, such as Raman or FTIR, providing a framework for autonomous decision-making in SDLs. △ Less

Submitted 24 January, 2026; v1 submitted 6 September, 2025; originally announced September 2025.

Comments: 37 Pages, 20 Figures

High-Quality Tomographic Image Reconstruction Integrating Neural Networks and Mathematical Optimization

Authors: Anuraag Mishra, Andrea Gilch, Benjamin Apeleo Zubiri, Jan Rolfes, Frauke Liers

Abstract: In this work, we develop a novel technique for reconstructing images from projection-based nano- and microtomography. Our contribution focuses on enhancing reconstruction quality, particularly for specimen composed of homogeneous material phases connected by sharp edges. This is accomplished by training a neural network to identify edges within subpictures. The trained network is then integrated i… ▽ More In this work, we develop a novel technique for reconstructing images from projection-based nano- and microtomography. Our contribution focuses on enhancing reconstruction quality, particularly for specimen composed of homogeneous material phases connected by sharp edges. This is accomplished by training a neural network to identify edges within subpictures. The trained network is then integrated into a mathematical optimization model, to reduce artifacts from previous reconstructions. To this end, the optimization approach favors solutions according to the learned predictions, however may also determine alternative solutions if these are strongly supported by the raw data. Hence, our technique successfully incorporates knowledge about the homogeneity and presence of sharp edges in the sample and thereby eliminates blurriness. Our results on experimental datasets show significant enhancements in interface sharpness and material homogeneity compared to benchmark algorithms. Thus, our technique produces high-quality reconstructions, showcasing its potential for advancing tomographic imaging techniques. △ Less

Submitted 7 September, 2025; originally announced September 2025.

Comments: 36 pages, 17 figures

MSC Class: 90C20; 94A08; 68U10

Pressure induced ferromagnetic to antiferromagnetic phase transition in transition metal chalcogenide Cr$_{3}$Te$_4$

Authors: Asish Kumar Mishra, Souvick Chakraborty, Bidisha Mukherjee, Mrinmay Sahu, Suvashree Mukherjee, Shubham Purwar, Harekrishna Bhunia, S. Thirupathaiah, Peter Liermann, Satyabrata Raj, Goutam Dev Mukherjee

Abstract: We have carried out a detailed high-pressure investigation on the strongly correlated transition metal chalcogenide $Cr_{3}Te_4$ using Raman spectroscopy and XRD, which is ferromagnetic and metallic at ambient conditions. We find that the monoclinic structure remains stable up to 30 GPa, the highest pressure studied. The Cr-Te bond length and octahedral volume decrease drastically up to 7.6 GPa pr… ▽ More We have carried out a detailed high-pressure investigation on the strongly correlated transition metal chalcogenide $Cr_{3}Te_4$ using Raman spectroscopy and XRD, which is ferromagnetic and metallic at ambient conditions. We find that the monoclinic structure remains stable up to 30 GPa, the highest pressure studied. The Cr-Te bond length and octahedral volume decrease drastically up to 7.6 GPa pressure. The $A_{1g}$ Raman mode shows a red shift up to 7.6 GPa, and the $E_g$ Raman mode shows a sudden drop around the same pressure. Further low-temperature Raman spectroscopic investigation shows that the Raman modes soften at the ferromagnetic to antiferromagnetic phase transition. This suggests a change in the magnetic ordering at high pressure. Our Density Functional Theory (DFT) calculations reveal the change in magnetic ground state from ferromagnetic state to antiferromagnetic state above 7.6 GPa pressure, corroborating our experimental result. △ Less

Submitted 10 July, 2025; originally announced July 2025.

Static treatment of dynamic interactions in the single-orbital Anderson impurity model

Authors: Anton Pauli, Akshat Mishra, Malte Rösner, Erik G. C. P. van Loon

Abstract: Correlated electron physics is intrinsically a multiscale problem, since high-energy electronic states screen the interactions between the correlated electrons close to the Fermi level, thereby reducing the magnitude of the interaction strength and dramatically shortening its range. Thus, the handling of screening is an essential ingredient in the first-principles modelling of correlated electron… ▽ More Correlated electron physics is intrinsically a multiscale problem, since high-energy electronic states screen the interactions between the correlated electrons close to the Fermi level, thereby reducing the magnitude of the interaction strength and dramatically shortening its range. Thus, the handling of screening is an essential ingredient in the first-principles modelling of correlated electron systems. Screening is an intrinsically dynamic process and the corresponding downfolding methods such as the constrained Random Phase Approximation indeed produce a dynamic interaction. However, many low-energy methods require an instantaneous interaction as input, which makes it necessary to map the fully dynamic interaction to an effective instantaneous interaction strength. It is a priori not clear if and when such an effective model can capture the physics of the one with dynamic interaction and how to best perform the mapping. Here, we provide a systematic benchmark relevant to correlated materials, in the form of the Anderson impurity model. Overall, we find that a static approximation can be valid and that the moment-based approach recently proposed by Scott and Booth can be a good tool to find the value of the static interaction. We also identify physical regimes, especially under doping, where an instantaneous interaction cannot capture all of the relevant physics. △ Less

Submitted 4 November, 2025; v1 submitted 8 July, 2025; originally announced July 2025.

Journal ref: Phys. Rev. B 112, 195101 (2025)

Phase field dislocation dynamics formulation coupled with Fourier based micromechanics solver and its application to grain boundary-dislocation interactions

Authors: Brayan Murgas, Avanish Mishra, Nithin Mathew, Abigail Hunter

Abstract: A new phase field dislocation dynamics formulation is presented, which couples micromechanical solvers and the time-dependent Ginzburg-Landau equation. Grain boundary (GB)-dislocation interactions are studied by describing GBs as inclusions. Grain boundary properties are computed from Molecular Statics simulations and an additional contribution to the total energy that takes into account the GB en… ▽ More A new phase field dislocation dynamics formulation is presented, which couples micromechanical solvers and the time-dependent Ginzburg-Landau equation. Grain boundary (GB)-dislocation interactions are studied by describing GBs as inclusions. Grain boundary properties are computed from Molecular Statics simulations and an additional contribution to the total energy that takes into account the GB energy is considered in the calculations. Interaction of a screw dislocation with minimum energy and metastable states of low and high angle $\langle$110$\rangle$ symmetric tilt grain boundaries are studied. We show good agreement between predictions from our phase field dislocation dynamics formulation and molecular dynamics simulations of grain boundary-dislocation interactions. △ Less

Submitted 18 February, 2026; v1 submitted 30 June, 2025; originally announced July 2025.

Comments: Main text 37 pages, entire text 58 pages

Report number: LA-UR-25-26159 Version 3

Lattice Mismatch Driven In Plane Strain Engineering for Enhanced Upper Critical Fields in Mo2N Superconducting Thin Films

Authors: Aditya Singh, Divya Rawat, Victor Hjort, Abhisek Mishra, Arnaud le Febvrier, Subhankar Bedanta, Per Eklund, Ajay Soni

Abstract: Transition metal nitrides are a fascinating class of hard coating material that provide an excellent platform for investigating superconductivity and fundamental electron phonon interactions. In this work the structural morphological and superconducting properties have been studied for Mo2N thin films deposited via direct current magnetron sputtering on cplane Al2O3 and MgO substrates to elucidate… ▽ More Transition metal nitrides are a fascinating class of hard coating material that provide an excellent platform for investigating superconductivity and fundamental electron phonon interactions. In this work the structural morphological and superconducting properties have been studied for Mo2N thin films deposited via direct current magnetron sputtering on cplane Al2O3 and MgO substrates to elucidate the effect of internal strain on superconducting properties. High resolution X Ray diffraction and time of flight elastic recoil detection analysis confirms the growth of single phase Mo2N thin films exhibiting epitaxial growth with twin domain structure. Low temperature electrical transport measurements reveal superconducting transitions at 5.2 K and 5.6 K with corresponding upper critical fields of 5 T and 7 T for the films deposited on Al2O3 and MgO, respectively. These results indicate strong type II superconductivity and the observed differences in superconducting properties are attributed to substrate induced strain which leads to higher e ph coupling for the film on MgO substrate. These findings highlight the tunability of superconducting properties in Mo2N films through strategic substrate selection. △ Less

Submitted 5 June, 2025; originally announced June 2025.

Engineering second order topological superconductor hosting tunable Majorana corner modes in magnet/$d$-wave superconductor hybrid platform

Authors: Minakshi Subhadarshini, Archana Mishra, Arijit Saha

Abstract: We theoretically study the noncollinear magnetic texture effect on second-order topological superconductor (SOTSC) phase generated in unconventional $d$-wave superconductors and two-dimensional (2D) quantum spin Hall insulators (QSHI). While the interplay of the $d$-wave superconductor and QSHI has been studied as a platform to realize Majorana corner modes (MCMs), we show that the addition of the… ▽ More We theoretically study the noncollinear magnetic texture effect on second-order topological superconductor (SOTSC) phase generated in unconventional $d$-wave superconductors and two-dimensional (2D) quantum spin Hall insulators (QSHI). While the interplay of the $d$-wave superconductor and QSHI has been studied as a platform to realize Majorana corner modes (MCMs), we show that the addition of the spin texture enables the tunability of these MCMs. Each corner of this hybrid system can host one or two Majorana modes depending on the system parameters, in particular, exchange strength and pitch vector of the spin texture. To characterize the higher order bulk topology, we compute the quadrupolar winding number, which directly corresponds to the number of MCMs acquiring a value of one for four corner modes and two for eight corner modes. We investigate and show the close resemblance in the topological phase diagrams obtained from the low energy effective Hamiltonian that reveals an emergent in-plane Zeeman field and spin-orbit coupling induced by the spin texture, and the real space tight binding lattice model. The microscopic pairing mechanism responsible for the appearance of SOTSC phase is investigated via an effective bulk pairing analysis, while a low-energy edge theory captures the mechanism behind tunability of MCMs. Our result paves the way for realizing SOTC with multiple MCMs which can be tuned via system parameters. △ Less

Submitted 6 October, 2025; v1 submitted 8 May, 2025; originally announced May 2025.

Comments: This is the published version

Journal ref: Phys. Rev. B 112, 125426 (2025)

Pressure-Induced Volume Collapse and Metallization in Inverse Spinel Co$_2$TiO$_4$

Authors: Mrinmay Sahu, Souvick Chakraborty, Bidisha Mukherjee, Bishnupada Ghosh, Asish Kumar Mishra, Satyabrata Raj, Goutam Dev Mukherjee

Abstract: The structural, vibrational, electronic, and magnetic properties of inverse spinel $Co_2TiO_4$ (CTO-Sp) under high-pressure (HP) conditions are systematically investigated using X-ray diffraction, Raman spectroscopy, in situ optical microscopy, and first-principles density functional theory (DFT) calculations. At ambient conditions, CTO-Sp exhibits a cubic phase with a space group $Fd\bar{3}m$, an… ▽ More The structural, vibrational, electronic, and magnetic properties of inverse spinel $Co_2TiO_4$ (CTO-Sp) under high-pressure (HP) conditions are systematically investigated using X-ray diffraction, Raman spectroscopy, in situ optical microscopy, and first-principles density functional theory (DFT) calculations. At ambient conditions, CTO-Sp exhibits a cubic phase with a space group $Fd\bar{3}m$, and it undergoes two notable structural phase transitions at HP. The first transition, occurring at approximately 7.3 GPa, leads to the tetragonal-$I4_1/amd$ phase with minimal alteration in unit cell volume. {The second transition takes place near 17.3 GPa, where two orthorhombic phases emerge and coexist above this pressure.} This second structural transition corresponds to a first-order phase transition involving a significant reduction in unit cell volume of approximately 17.5$\%$. The bulk compressibility of CTO-Sp and its HP post-spinel phases is almost equal to the average polyhedral compressibility within each phase. DFT calculations reveal a high-spin to low-spin transition, accompanied by the collapse of local magnetic moments in the $Cmcm$ orthorhombic phase, leading to the sample's pressure-induced metallization. △ Less

Submitted 28 June, 2025; v1 submitted 1 April, 2025; originally announced April 2025.

Soft mode induced structural phase transition in Ba$_2$ZnTeO$_6$ at high pressure

Authors: Bidisha Mukherjee, Surajit Adhikari, Mrinmay Sahu, Asish Kumar Mishra, Bhagyashri Giri, Priya Johari, Konstantin Glazyrin, Goutam Dev Mukherjee

Abstract: In this paper, we present a thorough investigation of vibrational, structural, and electronic properties of perovskite-type rhombohedral Ba$_2$ZnTeO$_6$ (BZTO) under systematic application of pressure. To carry out the analysis, we have performed pressure-dependent Raman spectroscopic measurements, synchrotron XRD, and density functional theory-based calculations. At ambient conditions, BZTO stabi… ▽ More In this paper, we present a thorough investigation of vibrational, structural, and electronic properties of perovskite-type rhombohedral Ba$_2$ZnTeO$_6$ (BZTO) under systematic application of pressure. To carry out the analysis, we have performed pressure-dependent Raman spectroscopic measurements, synchrotron XRD, and density functional theory-based calculations. At ambient conditions, BZTO stabilizes in $R\bar{3}m$ space group, which under pressure undergoes a structural transition to a monoclinic phase with space group $C2/m$ at around 18~GPa. In-depth Raman analysis reveals softening of a phonon mode E$_g$ ($\sim $ 28cm$^{-1}$) leads to the structural phase transition. First principle DFT calculations also indicate that the doubly degenerate soft mode associated with the in-phase TeO$_6$ octahedral rotation drives the structure to a lower symmetry phase $C2/m$. △ Less

Submitted 14 March, 2025; originally announced March 2025.

Fracture in concrete: X-ray tomography with in-situ testing, digital volume correlation and phase-field modeling

Authors: Akanksha Mishra, Pietro Carrara, Michele Griffa, Laura De Lorenzis

Abstract: We test and simulate the mesoscopic cracking behavior of specimens made of a standard concrete mixture. To this end, we combine stable wedge-splitting fracture experiments performed during X-ray tomography, their analysis with digital volume correlation providing the full three-dimensional displacement field, and phase-field cohesive fracture modeling. In our computations, we apply the measured bo… ▽ More We test and simulate the mesoscopic cracking behavior of specimens made of a standard concrete mixture. To this end, we combine stable wedge-splitting fracture experiments performed during X-ray tomography, their analysis with digital volume correlation providing the full three-dimensional displacement field, and phase-field cohesive fracture modeling. In our computations, we apply the measured boundary conditions and model the actual heterogeneous material structure at the mesoscopic scale. Within the phase-field model, we explicitly distinguish among (thus individually represent) the mesostructural features of distinct material phases with size above a threshold of 1 mm, while we homogenize pores and finer aggregates below this threshold within the cementitious mortar matrix, with material parameters characterized accordingly. We compare experimental and numerical results in terms of both local and global quantities. △ Less

Submitted 3 February, 2025; originally announced February 2025.

Shot-noise-driven macroscopic vibrations and displacement transduction in quantum tunnel junctions

Authors: Prasanta Kumbhakar, Anusha Shanmugam, Akhileshwar Mishra, Ravi Pant, J L Reno, S Addamane, Madhu Thalakulam

Abstract: Inherent randomness and the resulting stochastic behavior of fundamental particles manifested as quantum noise put a lower bound on measurement imprecision in the quantum measurement process. In addition, the quantum noise imparts decoherence and dephasing to the system being measured, referred to as the measurement back-action. While the microscopic effects of back-action have been observed, macr… ▽ More Inherent randomness and the resulting stochastic behavior of fundamental particles manifested as quantum noise put a lower bound on measurement imprecision in the quantum measurement process. In addition, the quantum noise imparts decoherence and dephasing to the system being measured, referred to as the measurement back-action. While the microscopic effects of back-action have been observed, macroscopic evidence is a rarity. Here we report a macroscopic display of the back-action of an ultra-sensitive quantum point contact (QPC) electrical amplifier whose transport is defined by the quantum tunneling of electrons. The QPC amplifier, realized on GaAs-AlGaAs heterostructures, coupled to a planar superconducting resonator, operates at a frequency of 2.155 GHz in the shot-noise-limited regime. The shot-noise excitation of the mechanical modes and the resulting piezoelectric polarization enhancing the shot-noise at the mode frequencies form a positive feedback loop between the electrical and mechanical degrees of freedom. While the excitation of the vibrational modes is a display of the macroscopic effects of measurement back-action, the amplitudes of the noise peaks allow us to calibrate the displacement sensitivity of the QPC-resonator systems, which is in the order of 35 fm/SQRT(Hz) range, making it an excellent sensor for ultra-sensitive and fast strain or displacement detection. △ Less

Submitted 19 January, 2025; originally announced January 2025.

Comments: 20 pages, includes supplementary informations

Advanced Displacement Magnitude Prediction in Multi-Material Architected Lattice Structure Beams Using Physics Informed Neural Network Architecture

Authors: Akshansh Mishra

Abstract: This paper proposes an innovative method for predicting deformation in architected lattice structures that combines Physics-Informed Neural Networks (PINNs) with finite element analysis. A thorough study was carried out on FCC-based lattice beams utilizing five different materials (Structural Steel, AA6061, AA7075, Ti6Al4V, and Inconel 718) under varied edge loads (1000-10000 N). The PINN model bl… ▽ More This paper proposes an innovative method for predicting deformation in architected lattice structures that combines Physics-Informed Neural Networks (PINNs) with finite element analysis. A thorough study was carried out on FCC-based lattice beams utilizing five different materials (Structural Steel, AA6061, AA7075, Ti6Al4V, and Inconel 718) under varied edge loads (1000-10000 N). The PINN model blends data-driven learning with physics-based limitations via a proprietary loss function, resulting in much higher prediction accuracy than linear regression. PINN outperforms linear regression, achieving greater R-square (0.7923 vs 0.5686) and lower error metrics (MSE: 0.00017417 vs 0.00036187). Among the materials examined, AA6061 had the highest displacement sensitivity (0.1014 mm at maximum load), while Inconel718 had better structural stability. △ Less

Submitted 30 December, 2024; originally announced January 2025.

Comments: 34 pages, 19 figures

Enhancement of spin Hall angle by an order of magnitude via Cu intercalation in MoS$_2$/CoFeB heterostructures

Authors: Abhisek Mishra, Pritam Das, Rupalipriyadarsini Chhatoi, Soubhagya Dash, Shubhransu Sahoo, Kshitij Singh Rathore, Pil-Ryung Cha, Seung-Cheol Lee, Satadeep Bhattacharjee, Subhankar Bedanta

Abstract: Transition metal dichalcogenides (TMDs) are a novel class of quantum materials with significant potential in spintronics, optoelectronics, valleytronics, and opto-valleytronics. TMDs exhibit strong spin-orbit coupling, enabling efficient spin-charge interconversion, which makes them ideal candidates for spin-orbit torque-driven spintronic devices. In this study, we investigated the spin-to-charge… ▽ More Transition metal dichalcogenides (TMDs) are a novel class of quantum materials with significant potential in spintronics, optoelectronics, valleytronics, and opto-valleytronics. TMDs exhibit strong spin-orbit coupling, enabling efficient spin-charge interconversion, which makes them ideal candidates for spin-orbit torque-driven spintronic devices. In this study, we investigated the spin-to-charge conversion through ferromagnetic resonance in MoS$_2$/Cu/CoFeB heterostructures with varying Cu spacer thicknesses. The conversion efficiency, quantified by the spin Hall angle, was enhanced by an order of magnitude due to Cu intercalation. Magneto-optic Kerr effect microscopy confirmed that Cu did not significantly modify the magnetic domains, indicating its effectiveness in decoupling MoS$_2$ from CoFeB. This decoupling preserves the spin-orbit coupling (SOC) of MoS$_2$ by mitigating the exchange interaction with CoFeB, as proximity to localized magnetization can alter the electronic structure and SOC. First-principles calculations revealed that Cu intercalation notably enhances the spin Berry curvature and spin Hall conductivity, contributing to the increased spin Hall angle. This study demonstrates that interface engineering of ferromagnet/TMD-based heterostructures can achieve higher spin-to-charge conversion efficiencies, paving the way for advancements in spintronic applications. △ Less

Submitted 1 December, 2025; v1 submitted 27 November, 2024; originally announced November 2024.

Emission enhancement and bandgap narrowing in $Cs_2TeBr_6$ under pressure

Authors: Debabrata Samanta, Suvashree Mukherjee, Asish Kumar Mishra, Bhagyashri Giri, Sonu Pratap Chaudhary, Konstantin Glazyrin, Sayan Bhattacharyya, Goutam Dev Mukherjee

Abstract: Pressure-induced emission enhancement and bandgap narrowing in vacancy-ordered halide double perovskite $Cs_2TeBr_6$ are extensively investigated through photoluminescence and absorption experiments. The below bandgap broad emission is attributed to self-trapped excitons recombination. The $Cs_2TeBr_6$ crystal, consisting of undistorted octahedra, exhibits substantial emission enhancement due to t… ▽ More Pressure-induced emission enhancement and bandgap narrowing in vacancy-ordered halide double perovskite $Cs_2TeBr_6$ are extensively investigated through photoluminescence and absorption experiments. The below bandgap broad emission is attributed to self-trapped excitons recombination. The $Cs_2TeBr_6$ crystal, consisting of undistorted octahedra, exhibits substantial emission enhancement due to the lowering of the energy barrier between $^3P_1$ and self-trapped exciton states, as well as the suppression of nonradiative energy loss with increasing pressure. In the Raman measurements, the observed behavior of full width at half maximum of all Raman modes implies dominant electron-phonon interactions rather than anharmonic interactions between phonons. The pressure-dependent X-ray diffraction measurements reveal an anomalous behaviour in the normalized pressure as a function of the Eulerian strain. △ Less

Submitted 15 October, 2024; originally announced October 2024.

Liquid Metal Oxide-assisted Integration of High-k Dielectrics and Metal Contacts for Two-Dimensional Electronics

Authors: Dasari Venkatakrishnarao, Abhishek Mishra, Yaoju Tarn, Michel Bosman, Rainer Lee, Sarthak Das, Subhrajit Mukherjee, Teymour Talha-Dean, Yiyu Zhang, Siew Lang Teo, Jian Wei Chai, Fabio Bussolotti, Kuan Eng Johnson Goh, Chit Siong Lau

Abstract: Two-dimensional van der Waals semiconductors are promising for future nanoelectronics. However, integrating high-k gate dielectrics for device applications is challenging as the inert van der Waals material surfaces hinder uniform dielectric growth. Here, we report a liquid metal oxide-assisted approach to integrate ultrathin, high-k HfO2 dielectric on 2D semiconductors with atomically smooth inte… ▽ More Two-dimensional van der Waals semiconductors are promising for future nanoelectronics. However, integrating high-k gate dielectrics for device applications is challenging as the inert van der Waals material surfaces hinder uniform dielectric growth. Here, we report a liquid metal oxide-assisted approach to integrate ultrathin, high-k HfO2 dielectric on 2D semiconductors with atomically smooth interfaces. Using this approach, we fabricated 2D WS2 top-gated transistors with subthreshold swings down to 74.5 mV/dec, gate leakage current density below 10-6 A/cm2, and negligible hysteresis. We further demonstrate a one-step van der Waals integration of contacts and dielectrics on graphene. This can offer a scalable approach toward integrating entire prefabricated device stack arrays with 2D materials. Our work provides a scalable solution to address the crucial dielectric engineering challenge for 2D semiconductors, paving the way for high-performance 2D electronics. △ Less

Submitted 19 September, 2024; originally announced September 2024.

Journal ref: ACS Nano, 2024

Toward Phonon-Limited Transport in Two-Dimensional Electronics by Oxygen-Free Fabrication

Authors: Subhrajit Mukherjee, Shuhua Wang, Dasari Venkatakrishnarao, Yaoju Tarn, Teymour Talha-Dean, Rainer Lee, Ivan A. Verzhbitskiy, Ding Huang, Abhishek Mishra, John Wellington John, Sarthak Das, Fabio Bussoloti, Thathsara D. Maddumapatabandi, Yee Wen Teh, Yee Sin Ang, Kuan Eng Johnson Goh, Chit Siong Lau

Abstract: Future electronics require aggressive scaling of channel material thickness while maintaining device performance. Two-dimensional (2D) semiconductors are promising candidates, but despite over two decades of research, experimental performance still lags theoretical expectations. Here, we develop an oxygen-free approach to push the electrical transport of 2D field-effect transistors toward the theo… ▽ More Future electronics require aggressive scaling of channel material thickness while maintaining device performance. Two-dimensional (2D) semiconductors are promising candidates, but despite over two decades of research, experimental performance still lags theoretical expectations. Here, we develop an oxygen-free approach to push the electrical transport of 2D field-effect transistors toward the theoretical phonon-limited intrinsic mobility. We achieve record carrier mobilities of 91 (132) cm2V-1s-1 for mono- (bi-) layer MoS2 transistors on SiO2 substrate. Statistics from over 60 devices confirm that oxygen-free fabrication enhances key figures of merit by more than an order of magnitude. While previous studies suggest that 2D transition metal dichalcogenides such as MoS2 and WS2 are stable in air, we show that short-term ambient exposure can degrade their device performance through irreversible oxygen chemisorption. This study emphasizes the criticality of avoiding oxygen exposure, offering guidance for device manufacturing for fundamental research and practical applications of 2D materials. △ Less

Submitted 12 September, 2024; originally announced September 2024.

Efficient spin to charge conversion and spin memory loss mitigation in oriented $\text{RuO}_2$ films

Authors: Abhisek Mishra, Kshitij Singh Rathore, Swayang Priya Mahanta, Subhankar Bedanta

Abstract: $\text{RuO}_2$, a transition metal oxide, is attracting attention in spintronics for its unique altermagnetic properties, which influence spin currents. Its ability to produce large spin-orbit torques and spin Hall effects is key for energy-efficient magnetic memory and logic devices. Additionally, the tunable thickness and crystallinity of $\text{RuO}_2… ▽ More $\text{RuO}_2$, a transition metal oxide, is attracting attention in spintronics for its unique altermagnetic properties, which influence spin currents. Its ability to produce large spin-orbit torques and spin Hall effects is key for energy-efficient magnetic memory and logic devices. Additionally, the tunable thickness and crystallinity of $\text{RuO}_2$ thin films optimize torque efficiency for low-power switching. Spin pumping, a versatile method for investigating spin dynamics in $\text{RuO}_2$ thin films, has garnered considerable interest because of its straightforward, non-invasive and uncomplicated approach to addressing impedance mismatch and direct measurement of spintronic parameters. Here we present a systematic and detailed analysis on the efficient spin to charge conversion in (110)-oriented $\text{RuO}_2$ films with amorphous CoFeB as spin source. The spin Hall angle, and spin diffusion length were estimated to be 0.14 $\pm$ 0.01 and 4.58 $\pm$ 0.40 nm, respectively. The spin Hall conductivity of 998.89 $\pm$ 58.23 $\hbar \cdot \frac{Ω^{-1} \, \text{cm}^{-1}}{e}$ has been estimated which is theoretically predicted to be of the similar order. The interfacial spin transparency has been achieved to be 90%. We have shown that the spin memory loss at the $\text{RuO}_2$/CoFeB interface is 15%, which is very small. △ Less

Submitted 18 August, 2024; originally announced August 2024.

Electronic, optical, and transport properties of alkali metal oxides (Cs2O): A DFT study

Authors: Anjali Kumari, Kamal Kumar, Abhishek Kumar Mishra, Ramesh Sharma

Abstract: The electronic, structural, optical, and thermoelectric properties of the Cs2O cubic structure have been investigated using density functional theory (DFT). The calculations utilize a full relativistic version of the full-potential augmented plane-wave plus local orbitals method, which is based on density functional theory, employing both the GGA and LDA approximations. Additionally, we employed t… ▽ More The electronic, structural, optical, and thermoelectric properties of the Cs2O cubic structure have been investigated using density functional theory (DFT). The calculations utilize a full relativistic version of the full-potential augmented plane-wave plus local orbitals method, which is based on density functional theory, employing both the GGA and LDA approximations. Additionally, we employed the GGA proposed by Trans-Blaha (GGA-mBJ) for band structure computations, revealing the indirect band gap nature of Cs2O. The optical properties are also addressed by computing the refractive index, extinction coefficient, and complex dielectric tensor. The electrical conductivity, Seebeck coefficient, and thermal conductivity exhibit temperature-dependent variations, indicating the formation of a thermoelectric material. Our findings indicate that the compound under investigation is categorized as a p-type semiconductor, with the majority of charge carriers responsible for conduction being holes rather than electrons. △ Less

Submitted 9 June, 2024; originally announced June 2024.

Comments: 21 pages

Machine Learning-Driven Optimization of TPMS Architected Materials Using Simulated Annealing

Authors: Akshansh Mishra

Abstract: The research paper presents a novel approach to optimizing the tensile stress of Triply Periodic Minimal Surface (TPMS) structures through machine learning and Simulated Annealing (SA). The study evaluates the performance of Random Forest, Decision Tree, and XGBoost models in predicting tensile stress, using a dataset generated from finite element analysis of TPMS models. The objective function mi… ▽ More The research paper presents a novel approach to optimizing the tensile stress of Triply Periodic Minimal Surface (TPMS) structures through machine learning and Simulated Annealing (SA). The study evaluates the performance of Random Forest, Decision Tree, and XGBoost models in predicting tensile stress, using a dataset generated from finite element analysis of TPMS models. The objective function minimized the negative R-squared value on the validation set to enhance model accuracy. The SA-XGBoost model outperformed the others, achieving an R-squared value of 0.96. In contrast, the SA-Random Forest model achieved an R squared value of 0.89 while the SA-Decision Tree model exhibited greater fluctuations in validation scores. This demonstrates that the SA-XGBoost model is most effective in capturing the complex relationships within the data. The integration of SA helps in optimizing the hyperparameters of these machine learning models, thereby enhancing their predictive capabilities. △ Less

Submitted 28 May, 2024; originally announced June 2024.

Comments: 25 Pages, 7 figures and 8 Tables

Learning from metastable grain boundaries

Authors: Avanish Mishra, Sumit A. Suresh, Saryu J. Fensin, Nithin Mathew, Edward M. Kober

Abstract: Grain boundaries (GBs) govern critical properties of polycrystals. Although significant advancements have been made in characterizing minimum energy GBs, real GBs are seldom found in such states, making it challenging to establish structure-property relationships. This diversity of atomic arrangements in metastable states motivates using data-driven methods to establish these relationships. In thi… ▽ More Grain boundaries (GBs) govern critical properties of polycrystals. Although significant advancements have been made in characterizing minimum energy GBs, real GBs are seldom found in such states, making it challenging to establish structure-property relationships. This diversity of atomic arrangements in metastable states motivates using data-driven methods to establish these relationships. In this study, we utilize a vast atomistic database (~5000) of minimum energy and metastable states of symmetric tilt copper GBs, combined with physically-motivated local atomic environment (LAE) descriptors (Strain Functional Descriptors, SFDs) to predict GB properties. Our regression models exhibit robust predictive capabilities using only 19 descriptors, generalizing to atomic environments in nanocrystals. A significant highlight of our work is integration of an unsupervised method with SFDs to elucidate LAEs at GBs and their role in determining properties. Our research underscores the role of a physics-based representation of LAEs and efficacy of data-driven methods in establishing GB structure-property relationships. △ Less

Submitted 31 May, 2024; originally announced June 2024.

DFT study of structural, electronic and optical properties of 2D MgO monolayer under bi-axial mechanical strain

Authors: Kamal Kumar, Anjali Kumari, Soni Mishra, Ramesh Sharma, Abhishek Kumar Mishra

Abstract: The structural, electronic, and dielectric (optical) properties of graphene-like 2D MgO monolayer have been explored through first-principles calculations under bi-axial tensile and compressive mechanical strain within a range of -10% to +10%. Our findings revealed that the pristine MgO monolayer is an indirect band gap semiconducting material and the semiconducting mature of MgO monolayer remains… ▽ More The structural, electronic, and dielectric (optical) properties of graphene-like 2D MgO monolayer have been explored through first-principles calculations under bi-axial tensile and compressive mechanical strain within a range of -10% to +10%. Our findings revealed that the pristine MgO monolayer is an indirect band gap semiconducting material and the semiconducting mature of MgO monolayer remains consistent under both compressive and tensile mechanical strain. This nature of MgO is confirmed through partial density of states (PDOS) as well as electronic band structure. PDOS exhibits the contribution of different atomic orbitals in bond formation and nature of bond, while band structure provides insight into electron transitions between energy levels of valance and conduction bands. All optical parameters (dielectric function, reflectivity, energy loss, refractive index, extinction coefficient and absorption) are plotted in an energy range 0-15 eV. Within this energy interval, MgO possesses the highest value of the refractive index (2.13) at 3.12 eV energy. Also, a detailed analysis of changes in the geometrical structure of MgO monolayer is provided. △ Less

Submitted 30 May, 2024; originally announced May 2024.

Comments: 6 figures

NH3 gas sensing over 2D Phosphorene sheet: A First-Principles Study

Authors: Naresh Kumar, Yogendra K. Gautam, Soni Mishra, Anuj Kumar, Abhishek Kumar Mishra

Abstract: First-principles based calculations were executed to investigate the sensing properties of ammonia gas molecules on two-dimensional pristine black phosphorene towards its application as a gas sensor and related applications. We discuss in detail, the interaction of ammonia gas molecules on the phosphorene single sheet through the structural change analysis, electronic band gap, Bader charge transf… ▽ More First-principles based calculations were executed to investigate the sensing properties of ammonia gas molecules on two-dimensional pristine black phosphorene towards its application as a gas sensor and related applications. We discuss in detail, the interaction of ammonia gas molecules on the phosphorene single sheet through the structural change analysis, electronic band gap, Bader charge transfer, and density-of-states calculations. Our calculations indicate that the phosphorene could be used as a detector of ammonia, where good sensitivity and very short recovery time at room temperature have confirmed the potential use of phosphorene in the detection of ammonia. △ Less

Submitted 16 May, 2024; originally announced May 2024.

Comments: 21 pages, Figures 8

The structure and migration of heavily irradiated grain boundaries and dislocations in Ni in the athermal limit

Authors: Ian Chesser, Peter M. Derlet, Avanish Mishra, Sarah Paguaga, Nithin Mathew, Khanh Dang, Blas Pedro Uberuaga, Abigail Hunter, Saryu Fensin

Abstract: The microstructural evolution at and near pre-existing grain boundaries (GBs) and dislocations in materials under high radiation doses is still poorly understood. In this work, we use the creation relaxation algorithm (CRA) developed for atomistic modeling of high-dose irradiation in bulk materials to probe the athermal limit of saturation of GB and dislocation core regions under irradiation in FC… ▽ More The microstructural evolution at and near pre-existing grain boundaries (GBs) and dislocations in materials under high radiation doses is still poorly understood. In this work, we use the creation relaxation algorithm (CRA) developed for atomistic modeling of high-dose irradiation in bulk materials to probe the athermal limit of saturation of GB and dislocation core regions under irradiation in FCC Ni. We find that, upon continuously subjecting a single dislocation or GB to Frenkel pair creation in the athermal limit, a local steady state disordered defect structure is reached with excess properties that fluctuate around constant values. Case studies are given for a straight screw dislocation which elongates into a helix under irradiation and several types of low and high angle GBs, which exhibit coupled responses such as absorption of extrinsic dislocations, roughening and migration. A positive correlation is found between initial GB energy and the local steady state GB energy under irradiation across a wide variety of GB types. Metastable GB structures with similar density in the defect core region but different initial configurations are found to converge to the same limiting structure under CRA. The mechanical responses of pristine and irradiated dislocations and GB structures are compared under an applied shear stress. Irradiated screw and edge dislocations are found to exhibit a hardening response, migrating at larger flow stresses than their pristine counterparts. Mobile GBs are found to exhibit softening or hardening responses depending on GB character. Although some GBs recover their initial pristine structures upon migration outside of the radiation zone, many GBs sustain different flow stresses corresponding to altered mobile core structures. △ Less

Submitted 7 May, 2024; originally announced May 2024.

Active Learning for Rapid Targeted Synthesis of Compositionally Complex Alloys

Authors: Nathan Johnson, Aashwin Ananda Mishra, Apurva Mehta

Abstract: The next generation of advanced materials is tending toward increasingly complex compositions. Synthesizing precise composition is time-consuming and becomes exponentially demanding with increasing compositional complexity. An experienced human operator does significantly better than a beginner but still struggles to consistently achieve precision when synthesis parameters are coupled. The time to… ▽ More The next generation of advanced materials is tending toward increasingly complex compositions. Synthesizing precise composition is time-consuming and becomes exponentially demanding with increasing compositional complexity. An experienced human operator does significantly better than a beginner but still struggles to consistently achieve precision when synthesis parameters are coupled. The time to optimize synthesis becomes a barrier to exploring scientifically and technologically exciting compositionally complex materials. This investigation demonstrates an Active Learning (AL) approach for optimizing physical vapor deposition synthesis of thin-film alloys with up to five principal elements. We compared AL based on Gaussian Process (GP) and Random Forest (RF) models. The best performing models were able to discover synthesis parameters for a target quinary alloy in 14 iterations. We also demonstrate the capability of these models to be used in transfer learning tasks. RF and GP models trained on lower dimensional systems (i.e. ternary, quarternary) show an immediate improvement in prediction accuracy compared to models trained only on quinary samples. Furthermore, samples that only share a few elements in common with the target composition can be used for model pre-training. We believe that such AL approaches can be widely adapted to significantly accelerate the exploration of compositionally complex materials. △ Less

Submitted 10 March, 2024; originally announced March 2024.

Magnon mediated spin pumping by coupled ferrimagnetic garnets heterostructure

Authors: Anupama Swain, Kshitij Singh Rathore, Pushpendra Gupta, Abhisek Mishra, Gary Lee, Jinho Lim, Axel Hoffmann, Ramanathan Mahendiran, Subhankar Bedanta

Abstract: Spin pumping has significant implications for spintronics, providing a mechanism to manipulate and transport spins for information processing. Understanding and harnessing spin currents through spin pumping is critical for the development of efficient spintronic devices. The use of a magnetic insulator with low damping, enhances the signal-to-noise ratio in crucial experiments such as spin-torque… ▽ More Spin pumping has significant implications for spintronics, providing a mechanism to manipulate and transport spins for information processing. Understanding and harnessing spin currents through spin pumping is critical for the development of efficient spintronic devices. The use of a magnetic insulator with low damping, enhances the signal-to-noise ratio in crucial experiments such as spin-torque ferromagnetic resonance (FMR) and spin pumping. A magnetic insulator coupled with a heavy metal or quantum material offers a more straight forward model system, especially when investigating spin-charge interconversion processes to greater accuracy. This simplicity arises from the absence of unwanted effects caused by conduction electrons unlike in ferromagnetic metals. Here, we investigate the spin pumping in coupled ferrimagnetic (FiM) Y3Fe5O12 (YIG)/Tm3Fe5O12 (TmIG) bilayers combined with heavy-metal (Pt) using the inverse spin Hall effect (ISHE). It is observed that magnon transmission occurs at both of the FiMs FMR positions. The enhancement of spin pumping voltage (Vsp) in the FiM garnet heterostructures is attributed to the strong interfacial exchange coupling between FiMs. The modulation of Vsp is achieved by tuning the bilayer structure. Further, the spin mixing conductance for these coupled systems is found to be 10^18 m^-2. Our findings describe a novel coupled FiM system for the investigation of magnon coupling providing new prospects for magnonic devices. △ Less

Submitted 6 February, 2024; originally announced February 2024.

Nano-ironing van der Waals Heterostructures Towards Electrically Controlled Quantum Dots

Authors: Teymour Talha-Dean, Yaoju Tarn, Subhrajit Mukherjee, John Wellington John, Ding Huang, Ivan A. Verzhbitskiy, Dasari Venkatakrishnarao, Sarthak Das, Rainer Lee, Abhishek Mishra, Shuhua Wang, Yee Sin Ang, Kuan Eng Johnson Goh, Chit Siong Lau

Abstract: Assembling two-dimensional van der Waals layered materials into heterostructures is an exciting development that sparked the discovery of rich correlated electronic phenomena and offers possibilities for designer device applications. However, resist residue from fabrication processes is a major limitation. Resulting disordered interfaces degrade device performance and mask underlying transport phy… ▽ More Assembling two-dimensional van der Waals layered materials into heterostructures is an exciting development that sparked the discovery of rich correlated electronic phenomena and offers possibilities for designer device applications. However, resist residue from fabrication processes is a major limitation. Resulting disordered interfaces degrade device performance and mask underlying transport physics. Conventional cleaning processes are inefficient and can cause material and device damage. Here, we show that thermal scanning probe based cleaning can effectively eliminate resist residue to recover pristine material surfaces. Our technique is compatible at both the material- and device-level, and we demonstrate the significant improvement in the electrical performance of 2D WS2 transistors. We also demonstrate the cleaning of van der Waals heterostructures to achieve interfaces with low disorder. This enables the electrical formation and control of quantum dots that can be tuned from macroscopic current flow to the single-electron tunnelling regime. Such material processing advances are crucial for constructing high-quality vdW heterostructures that are important platforms for fundamental studies and building blocks for quantum and nano-electronics applications. △ Less

Submitted 2 February, 2024; originally announced February 2024.

Comments: 4 Figures

Structural deformation and irreversible magnetic properties of flexible Co/Pt and Co/Pd thin films

Authors: Esita Pandey, Shaktiranjan Mohanty, Abhisek Mishra, Bhuvneshwari Sharma, Subhankar Bedanta

Abstract: The successful commercialization of flexible spintronic devices requires a complete understanding of the impact of external strain on the structural, electronic, and magnetic properties of a system. The impact of bending-induced strain on flexible films is studied quite well. However, little is known about the effect of other modes of flexibility, e.g., wrinkling, twisting, peeling, and stretching… ▽ More The successful commercialization of flexible spintronic devices requires a complete understanding of the impact of external strain on the structural, electronic, and magnetic properties of a system. The impact of bending-induced strain on flexible films is studied quite well. However, little is known about the effect of other modes of flexibility, e.g., wrinkling, twisting, peeling, and stretching on the functional properties of flexible films. In this context, perpendicular magnetic anisotropic Co/Pt and Co/Pd thin films are prepared on flexible Kapton substrates, and the impact of the peeling mode is studied in detail. The peeling method generates numerous cracks, and buckling in the thin film, along with localized blister formation imaged by scanning electron microscopy. Further, the resistivity measurement confirms a significant enhancement in sample resistance owing to the severe damage of the films. The structural discontinuities strongly affect the magnetization reversal phenomena as measured by the magneto-optic Kerr effect (MOKE)-based microscopy. The bubble domains got converted to elongated-shaped domains due to several hindrances to the wall motion after strain application. Further, the relaxation measurements reveal that the thermal energy is insufficient to switch the magnetization at a few areas due to their high pinning potential associated with the damages. In contrast to bending-induced strain, here, all the modifications in the functional properties are found to be irreversible in nature. △ Less

Submitted 31 December, 2023; originally announced January 2024.

Molecular Autonomous Pathfinder using Deep Reinforcement Learning

Authors: Ken-ichi Nomura, Ankit Mishra, Tian Sang, Rajiv K. Kalia, Aiichiro Nakano, Priya Vashishta

Abstract: Diffusion in solids is a slow process that dictates rate-limiting processes in key chemical reactions. Unlike crystalline solids that offer well-defined diffusion pathways, the lack of similar structural motifs in amorphous or glassy materials poses a great scientific challenge in estimating slow diffusion time. To tackle this problem, we have developed an AI-guided long-time atomistic simulation… ▽ More Diffusion in solids is a slow process that dictates rate-limiting processes in key chemical reactions. Unlike crystalline solids that offer well-defined diffusion pathways, the lack of similar structural motifs in amorphous or glassy materials poses a great scientific challenge in estimating slow diffusion time. To tackle this problem, we have developed an AI-guided long-time atomistic simulation approach: Molecular Autonomous Pathfinder (MAP) framework based on Deep Reinforcement Learning (RL), where RL agent is trained to uncover energy efficient diffusion pathways. We employ Deep Q-Network architecture with distributed prioritized replay buffer enabling fully online agent training with accelerated experience sampling by an ensemble of asynchronous agents. After training, the agents provide atomistic configurations of diffusion pathways with their energy profile. We use a piecewise Nudged Elastic Band to refine the energy profile of the obtained pathway and corresponding diffusion time on the basis of transition state theory. With MAP, we have successfully identified atomistic mechanisms along molecular diffusion pathways in amorphous silica, with time scales comparable to experiments. △ Less

Submitted 8 December, 2023; originally announced December 2023.

A Comparative Study of Coherent and Incoherent Drives in Four-Level Quantum Dot-Based Spaser

Authors: Ankit Purohit, Akhilesh Kumar Mishra

Abstract: In this article, we theoretically investigate a spaser (surface plasmon amplification by stimulated emission of radiation), which consists of a spherical silver nanoparticle surrounded by four-level gain medium of quantum dots (QDs). The spaser system is pumped coherently and incoherently with the same excitation rate, and the characteristics of coherent localized surface plasmon (LSP) mode, thus… ▽ More In this article, we theoretically investigate a spaser (surface plasmon amplification by stimulated emission of radiation), which consists of a spherical silver nanoparticle surrounded by four-level gain medium of quantum dots (QDs). The spaser system is pumped coherently and incoherently with the same excitation rate, and the characteristics of coherent localized surface plasmon (LSP) mode, thus produced, are compared for the two pumping scenarios. We provide a detailed analytical expression for the steady state and show that the incoherent pump is more suitable for the continuous spaser mode. The reason is better understood by studying the temporal evolution of number of LSP (N_n ), where the oscillation of LSP starts early for incoherent drive and relaxes to steady state with a large value of N_n. At a large pump rate, spaser curve shows saturation. In addition, we have found that the resonance peak of spaser field is independent of coherent as well as incoherent pumping, while the peak amplitude of field depends on the pump rate. △ Less

Submitted 5 February, 2024; v1 submitted 8 September, 2023; originally announced September 2023.

Comments: 12 pages, 6 figures

Journal ref: Journal of Optics (IOP) 26, 035001 (2024)

Controlling Majorana hybridization in magnetic chain-superconductor systems

Authors: Oladunjoye A. Awoga, Ioannis Ioannidis, Archana Mishra, Martin Leijnse, Mircea Trif, Thore Posske

Abstract: We propose controlling the hybridization between Majorana zero modes at the ends of magnetic adatom chains on superconductors by an additional magnetic adatom deposited close by. By tuning the additional adatom's magnetization, position, and coupling to the superconductor, we can couple and decouple the Majorana modes as well as control the ground state parity. The scheme is independent of microsc… ▽ More We propose controlling the hybridization between Majorana zero modes at the ends of magnetic adatom chains on superconductors by an additional magnetic adatom deposited close by. By tuning the additional adatom's magnetization, position, and coupling to the superconductor, we can couple and decouple the Majorana modes as well as control the ground state parity. The scheme is independent of microscopic details in ferromagnetic and helical magnetic chains on superconductors with and without spin-orbit coupling, which we show by studying their full microscopic models and their common low-energy description. Our results show that scanning tunneling microscopy and electron spin resonance techniques are promising tools for controlling the Majorana hybridization in magnetic adatoms-superconductor setups, providing a basis for Majorana parity measurements, fusion, and braiding techniques. △ Less

Submitted 17 August, 2024; v1 submitted 15 August, 2023; originally announced August 2023.

Comments: Published version

Journal ref: Phys. Rev. Res. 6, 033154 (2024)

JARVIS-Leaderboard: A Large Scale Benchmark of Materials Design Methods

Authors: Kamal Choudhary, Daniel Wines, Kangming Li, Kevin F. Garrity, Vishu Gupta, Aldo H. Romero, Jaron T. Krogel, Kayahan Saritas, Addis Fuhr, Panchapakesan Ganesh, Paul R. C. Kent, Keqiang Yan, Yuchao Lin, Shuiwang Ji, Ben Blaiszik, Patrick Reiser, Pascal Friederich, Ankit Agrawal, Pratyush Tiwary, Eric Beyerle, Peter Minch, Trevor David Rhone, Ichiro Takeuchi, Robert B. Wexler, Arun Mannodi-Kanakkithodi , et al. (13 additional authors not shown)

Abstract: Lack of rigorous reproducibility and validation are major hurdles for scientific development across many fields. Materials science in particular encompasses a variety of experimental and theoretical approaches that require careful benchmarking. Leaderboard efforts have been developed previously to mitigate these issues. However, a comprehensive comparison and benchmarking on an integrated platform… ▽ More Lack of rigorous reproducibility and validation are major hurdles for scientific development across many fields. Materials science in particular encompasses a variety of experimental and theoretical approaches that require careful benchmarking. Leaderboard efforts have been developed previously to mitigate these issues. However, a comprehensive comparison and benchmarking on an integrated platform with multiple data modalities with both perfect and defect materials data is still lacking. This work introduces JARVIS-Leaderboard, an open-source and community-driven platform that facilitates benchmarking and enhances reproducibility. The platform allows users to set up benchmarks with custom tasks and enables contributions in the form of dataset, code, and meta-data submissions. We cover the following materials design categories: Artificial Intelligence (AI), Electronic Structure (ES), Force-fields (FF), Quantum Computation (QC) and Experiments (EXP). For AI, we cover several types of input data, including atomic structures, atomistic images, spectra, and text. For ES, we consider multiple ES approaches, software packages, pseudopotentials, materials, and properties, comparing results to experiment. For FF, we compare multiple approaches for material property predictions. For QC, we benchmark Hamiltonian simulations using various quantum algorithms and circuits. Finally, for experiments, we use the inter-laboratory approach to establish benchmarks. There are 1281 contributions to 274 benchmarks using 152 methods with more than 8 million data-points, and the leaderboard is continuously expanding. The JARVIS-Leaderboard is available at the website: https://pages.nist.gov/jarvis_leaderboard △ Less

Submitted 26 March, 2024; v1 submitted 20 June, 2023; originally announced June 2023.

Generalized model of incipient plasticity with parametric variations

Authors: Sweta Kumari, Aditya Vardhan Mishra, Amlan Dutta

Abstract: Incipient plasticity is typically associated with thermally activated events like the nucleation of dislocations in crystalline solids and the activation of shear transformation zones in metallic glasses. A widely employed method of estimating the activation parameters of such mechanisms involves analyzing the statistical distribution of critical loads obtained through a series of repeated measure… ▽ More Incipient plasticity is typically associated with thermally activated events like the nucleation of dislocations in crystalline solids and the activation of shear transformation zones in metallic glasses. A widely employed method of estimating the activation parameters of such mechanisms involves analyzing the statistical distribution of critical loads obtained through a series of repeated measurements. However, the conventional mathematical approach assumes the activation parameters to remain fixed during the sequence of measurements. The present study critically examines this premise and presents a generalized statistical model that allows the statistical variations of activation parameters. Using a simple Monte Carlo scheme, it is demonstrated that even small fluctuations of activation parameters can significantly affect the statistical distribution of measured critical loads. The Monte Carlo calculations, along with atomistic simulations, further show that imposing the assumption of rigidly fixed parameters on an activated process with parametric fluctuations can lead to severe underestimation of the activation parameters. As many experimental studies have consistently reported perplexingly small activation volumes estimated using the conventional statistical approach, we propose that our findings can offer a fresh perspective on this longstanding issue. △ Less

Submitted 23 October, 2024; v1 submitted 13 June, 2023; originally announced June 2023.

Comments: 7 figures, 2 tables