arXiv subjects

Kapil Gupta

Publications and source records attributed to Kapil Gupta.

10 recordsLinked to original sources

arXiv2026

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

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.

cond-mat.mtrl-sci↗

arXiv2026

Intelligent Elastic Feature Fading: Enabling Model Retrain-Free Feature Efficiency Rollouts at Scale

Large-scale ranking systems depend on thousands of features derived from user behavior across multiple time horizons. Typically requires model retraining -- resulting in long iteration cycles (3--6 months), substantial GPU resource consumption, and limited rollout throughput. We introduce Intelligent Elastic Feature Fading (IEFF), a production infrastructure system that enables retrain-free feature efficiency rollouts by elastically controlling feature coverage and distribution at serving time. IEFF supports incremental feature coverage adjustments while models adapt through recurring training, eliminating dependencies on explicit retraining cycles. The system incorporates strict safety guardrails, reversibility mechanisms, and comprehensive monitoring to ensure stability at scale. Across multiple production use cases, IEFF accelerates efficiency-related rollouts by 5$\times$, eliminates retraining-related GPU overhead, and enables faster capacity recycling. Extensive offline and online experiments demonstrate that gradual feature fading prevents 50--55\% of online performance degradation compared to abrupt feature removal, while maintaining stable model behavior. These results establish elastic, system-level feature fading as a practical and scalable approach for managing feature efficiency in modern industrial ranking systems.

cs.IR↗

arXiv2026

Strain-Mediated Lattice Reconstruction Enhances Ferromagnetism in Cr2Ge2Te6/WTe2 van der Waals Heterobilayers

Van der Waals (vdW) heterostructures enable tailored electronic and magnetic phases by stacking atomically thin layers with pristine interfaces. Here, we investigate fully 2D Cr2Ge2Te6/WTe2 heterostructures and identify a strong enhancement of ferromagnetism in Cr2Ge2Te6 (CGT). Magnetotransport measurements across multiple devices with WTe2 thicknesses ranging from monolayer to bulk reveal a robust anomalous Hall effect together with a more than twofold increase of the Curie temperature and substantially enhanced coercive fields. Interface microscopy confirms chemically abrupt vdW interfaces with no detectable interdiffusion, while control experiments rule out processing- or stray-field-induced artifacts. Our experiments and theoretical calculations demonstrate that interfacial charge transfer renders CGT conductive and that proximity-induced lattice distortions in CGT enhance exchange and magnetocrystalline anisotropy. These results establish strain-mediated lattice reconstruction as a strategy for engineering high-temperature magnetic order in 2D heterostructures and clarify that modifications within the magnetic layer itself can govern proximity effects in vdW stacks.

cond-mat.mtrl-sci↗

arXiv2025

Polarization Vortices in a Ferromagnetic Metal via Twistronics

Recent advances in moire engineering provide new pathways for manipulating lattice distortions and electronic properties in low-dimensional materials. Here, we demonstrate that twisted stacking can induce dipolar vortices in metallic SrRuO3 membranes, despite the presence of free charges that would normally screen depolarizing fields and dipole-dipole interactions. These polarization vortices are correlated with moire-periodic flexoelectricity induced by shear strain gradients, and exhibit a pronounced dependence on the twist angle. In addition, multiferroic behavior emerges below the ferromagnetic Curie temperature of the films, whereby polarization and ferromagnetism coexist and compete, showing opposite twist-angle dependencies of their respective magnitudes. Density functional theory calculations provide insights into the microscopic origin of these observations. Our findings extend the scope of polarization topology design beyond dielectric materials and into metals.

cond-mat.mtrl-sci↗

arXiv2024

A divide-and-conquer approach for spatio-temporal analysis of large house price data from Greater London

Statistical research in real estate markets, particularly in understanding the spatio-temporal dynamics of house prices, has garnered significant attention in recent times. Although Bayesian methods are common in spatio-temporal modeling, standard Markov chain Monte Carlo (MCMC) techniques are usually slow for large datasets such as house price data. To tackle this problem, we propose a divide-and-conquer spatio-temporal modeling approach. This method involves partitioning the data into multiple subsets and applying an appropriate Gaussian process model to each subset in parallel. The results from each subset are then combined using the Wasserstein barycenter technique to obtain the global parameters for the original problem. The proposed methodology allows for multiple observations per spatial and time unit, thereby offering added benefits for practitioners. As a real-life application, we analyze house price data of more than 0.6 million transactions from 983 middle layer super output areas in London over a period of eight years. The methodology provides insightful findings about the effects of various amenities, trend patterns, and the relationship between prices and carbon emissions. Furthermore, as demonstrated through a cross-validation study, it shows good predictive accuracy while balancing computational efficiency.

stat.AP↗

arXiv2022

A review and recommendations on variable selection methods in regression models for binary data

The selection of essential variables in logistic regression is vital because of its extensive use in medical studies, finance, economics and related fields. In this paper, we explore four main typologies (test-based, penalty-based, screening-based, and tree-based) of frequentist variable selection methods in logistic regression setup. Primary objective of this work is to give a comprehensive overview of the existing literature for practitioners. Underlying assumptions and theory, along with the specifics of their implementations, are detailed as well. Next, we conduct a thorough simulation study to explore the performances of fifteen different methods in terms of variable selection, estimation of coefficients, prediction accuracy as well as time complexity under various settings. We take low, moderate and high dimensional setups and consider different correlation structures for the covariates. A real-life application, using a high-dimensional gene expression data, is also included in this study to further understand the efficacy and consistency of the methods. Finally, based on our findings in the simulated data and in the real data, we provide recommendations for practitioners on the choice of variable selection methods under various contexts.

stat.ME↗

arXiv2018

Role of zero-point effects in stabilizing the ground state structure of bulk Fe2P

Structural stability of Fe2P is investigated in detail using first-principles calculations based on density functional theory. While the orthorhombic C23 phase is found to be energetically more stable, the experiments suggest it to be hexagonal C22 phase. In the present study, we show that in order to obtain the correct ground state structure of Fe2P from the first-principles based methods it is utmost necessary to consider the zero-point effects such as zero-point vibrations and spin fluctuations. This study demonstrates an exceptional case where a bulk material is stabilized by quantum effects, which are usually important in low-dimensional materials. Our results also indicate the possibility of magnetic field induced structural quantum phase transition in Fe2P, which should form the basis for further theoretical and experimental efforts.

cond-mat.mtrl-sci↗

arXiv2014

Strain induced metal-insulator transition in ultrathin films of SrRuO$_3$

The ultrathin film limit has been shown to be a rich playground for unusual low dimensional physics. Taking the example of SrRuO$_3$ which is ferromagnetic and metallic at the bulk limit, one finds that it becomes antiferromagnetic and insulating at the three monolayers limit when grown on SrTiO$_3$. The origin of the insulating state is traced to strongly orbital dependent exchange splittings. A modest compressive strain of 1% of the SrTiO$_3$ substrate is then found to drive the system into a highly confined two-dimensional 100% spin polarized metallic state. This metal-insulator transition driven by a modest strain could be useful in two state device applications.

cond-mat.mtrl-sci↗

arXiv2013

Orbital ordering induced ferroelectricity in SrCrO3

Using density functional theory calculations, ultrathin films of SrVO3(d1) and SrCrO3(d2) on SrTiO3 substrates have been studied as possible multiferroics. Although both are metallic in the bulk limit, they are found to be insulating as a result of orbital ordering driven by lattice distortions at the ultrathin limit. While the distortions in SrVO3 have a first-order Jahn-Teller origin, those in SrCrO3 are ferroelectric in nature. This route to ferroelectricity (FE) results in polarizations comparable with conventional ferroelectrics.

cond-mat.mtrl-sci↗

arXiv2009

Strain driven magnetism in thin films of LaCoO3

The electronic structure of epitaxial films on LaCoO3(LCO) has been studied within first principle electronic structure calculations. A spin state transition is found to take place as a function of lattice strain which freezes in the intermediate spin state for non zero strain. In contrast to earlier speculations this is found to arise from substrate strain alone and angle variations are small. The intermediate spin state also stabilizes ferromagnetism in the ground state. The anomalous temperature dependence of the X-ray absorption spectra for films of LCO on LCO and its absence in films of LCO on (LaAlO_{3})_{0.3}(SrAlTaO_{6})_{0.7}$(LSAT) is also explained.

cond-mat.str-el↗