arXiv subjects

Debashis Mondal

Publications and source records attributed to Debashis Mondal.

13 recordsLinked to original sources

arXiv2024

Imprinting electrically switchable scalar spin chirality by anisotropic strain in a Kagome antiferromagnet

Topological chiral antiferromagnets, such as Mn$_{3}$Sn, are emerging as promising materials for next-generation spintronic devices due to their intrinsic transport properties linked to exotic magnetic configurations. Here, we demonstrate that anisotropic strain in Mn$_{3}$Sn thin films offers a novel approach to manipulate the magnetic ground state, unlocking new functionalities in this material. Anisotropic strain reduces the point group symmetry of the manganese (Mn) Kagome triangles from $C_{3v}$ to $C_{1}$, significantly altering the energy landscape of the magnetic states in Mn$_{3}$Sn. This symmetry reduction enables even a tiny in-plane Dzyaloshinskii-Moriya (DM) interaction to induce canting of the Mn spins out of the Kagome plane. The modified magnetic ground state introduces a finite scalar spin chirality and results in a significant Berry phase in momentum space. Consequently, a large anomalous Hall effect emerges in the Kagome plane at room temperature - an effect that is absent in the bulk material. Moreover, this two-fold degenerate magnetic state enables the creation of multiple-stable, non-volatile anomalous Hall resistance (AHR) memory states. These states are field-stable and can be controlled by thermal assisted current-induced magnetization switching requiring modest current densities and small bias fields, thereby offering a compelling new functionality in Mn$_{3}$Sn for spintronic applications.

cond-mat.mtrl-sci↗

arXiv2023

Discovery of a magnetic Dirac system with large intrinsic non-linear Hall effect

Magnetic materials exhibiting topological Dirac fermions are attracting significant attention for their promising technological potential in spintronics. In these systems, the combined effect of the spin-orbit coupling and magnetic order enables the realization of novel topological phases with exotic transport properties, including the anomalous Hall effect and magneto-chiral phenomena. Herein, we report experimental signature of topological Dirac antiferromagnetism in TaCoTe2 via angle-resolved photoelectron spectroscopy (ARPES) and first-principles density functional theory (DFT) calculations. In particular, we find the existence of spin-orbit coupling-induced gaps at the Fermi level, consistent with the manifestation of a large intrinsic non-linear Hall conductivity. Remarkably, we find that the latter is extremely sensitive to the orientation of the Néel vector, suggesting TaCoTe2 a suitable candidate for the realization of non-volatile spintronic devices with an unprecedented level of intrinsic tunability.

cond-mat.str-el↗

arXiv2022

Disentangling structural and electronic properties in V$_{2}$O$_{3}$ thin films: a genuine non-symmetry breaking Mott transition

Phase transitions are key in determining and controlling the quantum properties of correlated materials. Here, by using the powerful combination of precise material synthesis and angle resolved photoelectron spectroscopy, we show evidence for a genuine Mott transition undressed of any symmetry breaking side effects in the thin-films of V$_{2}$O$_{3}$. In particular, and in sharp contrast with the bulk V$_{2}$O$_{3}$ crystals, we unveil the purely electronic dynamics approaching the metal-insulator transition, disentangled from the structural transformation that is prevented by the residual substrate-induced strain. On approaching the transition, the spectral signal evolves surprisingly slowly over a wide temperature range, the Fermi wave-vector does not change, and the critical temperature appears to be much lower than the one reported for the bulk. Our findings are on one side fundamental in demonstrating the universal benchmarks of a genuine non-symmetry breaking Mott transition, extendable to a large array of correlated quantum systems and, on the other, given that the fatal structural breakdown is avoided, they hold promise of exploiting the metal-insulator transition by implementing V$_{2}$O$_{3}$ thin films in devices.

cond-mat.str-el↗

arXiv2022

VizInspect Pro -- Automated Optical Inspection (AOI) solution

Traditional vision based Automated Optical Inspection (referred to as AOI in paper) systems present multiple challenges in factory settings including inability to scale across multiple product lines, requirement of vendor programming expertise, little tolerance to variations and lack of cloud connectivity for aggregated insights. The lack of flexibility in these systems presents a unique opportunity for a deep learning based AOI system specifically for factory automation. The proposed solution, VizInspect pro is a generic computer vision based AOI solution built on top of Leo - An edge AI platform. Innovative features that overcome challenges of traditional vision systems include deep learning based image analysis which combines the power of self-learning with high speed and accuracy, an intuitive user interface to configure inspection profiles in minutes without ML or vision expertise and the ability to solve complex inspection challenges while being tolerant to deviations and unpredictable defects. This solution has been validated by multiple external enterprise customers with confirmed value propositions. In this paper we show you how this solution and platform solved problems around model development, deployment, scaling multiple inferences and visualizations.

cs.AI↗

arXiv2022

On the usefulness of lattice approximations for fractional Gaussian fields

Fractional Gaussian fields provide a rich class of spatial models and have a long history of applications in multiple branches of science. However, estimation and inference for fractional Gaussian fields present significant challenges. This book chapter investigates the use of the fractional Laplacian differencing on regular lattices to approximate to continuum fractional Gaussian fields. Emphasis is given on model based geostatistics and likelihood based computations. For a certain range of the fractional parameter, we demonstrate that there is considerable agreement between the continuum models and their lattice approximations. For that range, the parameter estimates and inferences about the continuum fractional Gaussian fields can be derived from the lattice approximations. Interestingly, regular lattice approximations facilitate fast matrix-free computations and enable anisotropic representations. We illustrate the usefulness of lattice approximations via simulation studies and by analyzing sea surface temperature on the Indian Ocean.

stat.ME↗

arXiv2021

Magnetic Topological Semimetal Phase with Electronic Correlation Enhancement in SmSbTe

The ZrSiS family of compounds hosts various exotic quantum phenomena due to the presence of both topological nonsymmorphic Dirac fermions and nodal-line fermions. In this material family, the LnSbTe (Ln= lanthanide) compounds are particularly interesting owing to the intrinsic magnetism from magnetic Ln which leads to new properties and quantum states. In this work, the authors focus on the previously unexplored compound SmSbTe. The studies reveal a rare combination of a few functional properties in this material, including antiferromagnetism with possible magnetic frustration, electron correlation enhancement, and Dirac nodal-line fermions. These properties enable SmSbTe as a unique platform to explore exotic quantum phenomena and advanced functionalities arising from the interplay between magnetism, topology, and electronic correlations.

cond-mat.mtrl-sci↗

arXiv2021

The C-SHIFT algorithm for normalizing covariances

Omics technologies are powerful tools for analyzing patterns in gene expression data for thousands of genes. Due to a number of systematic variations in experiments, the raw gene expression data is often obfuscated by undesirable technical noises. Various normalization techniques were designed in an attempt to remove these non-biological errors prior to any statistical analysis. One of the reasons for normalizing data is the need for recovering the covariance matrix used in gene network analysis. In this paper, we introduce a novel normalization technique, called the covariance shift (C-SHIFT) method. This normalization algorithm uses optimization techniques together with the blessing of dimensionality philosophy and energy minimization hypothesis for covariance matrix recovery under additive noise (in biology, known as the bias). Thus, it is perfectly suited for the analysis of logarithmic gene expression data. Numerical experiments on synthetic data demonstrate the method's advantage over the classical normalization techniques. Namely, the comparison is made with Rank, Quantile, cyclic LOESS (locally estimated scatterplot smoothing), and MAD (median absolute deviation) normalization methods. We also evaluate the performance of C-SHIFT algorithm on real biological data.

q-bio.GN↗

arXiv2019

Low-energy type-II Dirac fermions and spin-polarized topological surface states in transition-metal dichalcogenide NiTe$_2$

Using spin- and angle- resolved photoemission spectroscopy (spin-ARPES) together with ${\it ab~initio}$ calculations, we demonstrate the existence of a type-II Dirac semimetal state in NiTe$_2$. We show that, unlike PtTe$_2$, PtSe$_2$, and PdTe$_2$, the Dirac node in NiTe$_2$ is located in close vicinity of the Fermi energy. Additionally, NiTe$_2$ also hosts a pair of band inversions below the Fermi level along the $Γ-A$ high-symmetry direction, with one of them leading to a Dirac cone in the surface states. The bulk Dirac nodes and the ladder of band inversions in NiTe$_2$ support unique topological surface states with chiral spin texture over a wide range of energies. Our work paves the way for the exploitation of the low-energy type-II Dirac fermions in NiTe$_2$ in the fields of spintronics, THz plasmonics and ultrafast optoelectronics.

cond-mat.mes-hall↗

arXiv2018

An experimental and Ab-initio study of Electronic and Magnetic properties of FeGa3

Electronic structure of FeGa3 has been studied using experiments and ab-initio calculations. Magnetization measurements show that FeGa3 is inherently diamagnetic in nature. Our studies indicate that the previously reported magnetic moment on the Fe atoms in FeGa3 is not an intrinsic property of FeGa3, but is primarily due to the presence of disorder, defects, grain boundaries etc that break the symmetry about the Fe dimers. Analysis of the results obtained from magnetic measurements, photoelectron spectroscopy, Fe K-edge X-ray absorption near edge spectroscopy and ab-initio calculations clearly indicates that, the effects of on-site Coulomb repulsion between the Fe 3d electrons do not play any role in determining the electronic and magnetic properties of FeGa3. Detailed analysis of results of single crystal and poycrystalline FeGa3, helps to resolve the discrepancy in the electronic and magnetic properties in FeGa3 existing in the literature, consistently.

cond-mat.mtrl-sci↗

arXiv2017

High pressure studies on properties of FeGa3: role of on-site coulomb correlation

High pressure X-ray diffraction measurements have been carried out on the intermetallic semiconductor FeGa$_3$ and the equation of state for FeGa$_3$ has been determined. First principles based DFT calculations within the GGA approximation indicate that although the unit cell volume matches well with the experimentally obtained value at ambient pressure, it is significantly underestimated at high pressures and the difference between them increases as pressure increases. GGA + U calculations with increasing values of U$_{Fe(3d)}$ (on-site Coulomb repulsion between the Fe 3d electrons) at high pressures, correct this discrepancy. Further, the GGA+U calculations also show that along with U$_{Fe(3d)}$, the Fe 3d band width also increases with pressure and around a pressure of 4 GPa, a small density of states appear at the Fermi level. High pressure resistance measurements carried out on FeGa$_3$ also clearly show a signature of an electronic transition. Beyond the pressure of 19.7 GPa, the diffraction peaks reduce in intensity and are not observable beyond $\sim$ 26 GPa, leading to an amorphous state.

cond-mat.mtrl-sci↗

arXiv2016

Structural and electronic properties of Fe(AlxGa1-x)3 system

FeGa3 is a well known d-p hybridization induced intermetallic bandgap semiconductor. In this work, we present the experimental and theoretical results on the effect of Al substitution in FeGa3, obtained by x-ray diffraction (XRD), temperature dependent resistance measurement, room temperature Mossbauer measurements and density functional theory based electronic structure calculations. It is observed that upto x = 0.178 in Fe(AlxGa1-x)3, which is the maximum range studied in this work, Al substitution reduces the lattice parameters 'a' and 'c' preserving the parent tetragonal P42/mnm crystal structure of FeGa3. The bandgap of Fe(AlxGa1-x)3 for x = 0.178 is reduced by ~ 24% as compared to FeGa3. Rietveld refinement of the XRD data shows that the Al atoms replace Ga atoms located at the 8j sites in FeGa3. A comparison of the trends of the lattice parameters and energy bandgap observed in the calculations and the experiments also confirms that Al primarily replaces the Ga atoms in the 8j site.

cond-mat.mtrl-sci↗

arXiv2016

Electronic Structure of FeAl Alloy Studied by Resonant Photoemission Spectroscopy and Ab Initio Calculations

Resonant photoemission spectroscopy has been used to investigate the character of Fe 3d states in FeAl alloy. Fe 3d states have two different character, first is of itinerant nature located very close to the Fermi level, and second, is of less itinerant (relatively localized character), located beyond 2 eV below the Fermi level. These distinct states are clearly distinguishable in the resonant photoemission data. Comparison between the results obtained from experiments and first principle based electronic structure calculation show that the origin of the itinerant character of the Fe 3d states is due to the ordered B2 structure, whereas the relatively less itinerant (localized) Fe 3d states are from the disorders present in the sample. The exchange splitting of the Fe 3s core level peak confirms the presence of local moment in this system. It is found that the itinerant electrons arise due to the hybridization between Fe 3d and Al 3s-3p states. Presence of hybridization is observed as a shift in the Al 2p core-level spectra as well as in the X-ray near edge absorption spectra towards lower binding energy. Our photoemission results are thus explained by the co-existence of ordered and disordered phases in the system.

cond-mat.mtrl-sci↗

arXiv2015

Applying Dynkin's isomorphism: An alternative approach to understand the Markov property of the de Wijs process

Dynkin's (Bull. Amer. Math. Soc. 3 (1980) 975-999) seminal work associates a multidimensional transient symmetric Markov process with a multidimensional Gaussian random field. This association, known as Dynkin's isomorphism, has profoundly influenced the studies of Markov properties of generalized Gaussian random fields. Extending Dykin's isomorphism, we study here a particular generalized Gaussian Markov random field, namely, the de Wijs process that originated in Georges Matheron's pioneering work on mining geostatistics and, following McCullagh (Ann. Statist. 30 (2002) 1225-1310), is now receiving renewed attention in spatial statistics. This extension of Dynkin's theory associates the de Wijs process with the (recurrent) Brownian motion on the two dimensional plane, grants us further insight into Matheron's kriging formula for the de Wijs process and highlights previously unexplored relationships of the central Markov models in spatial statistics with Markov processes on the plane.

math.ST↗