arXiv subjects

Nirmal Ganguli

Publications and source records attributed to Nirmal Ganguli.

At least 19 recordsLinked to original sources

arXiv2026

Valley polarization, Rashba interaction, and weak altermagnetism in inversion-asymmetric MnPS$_\text{3}|$WS$_\text{2}$ van der Waals heterostructures

The deliberate breaking of inversion ($\mathcal{P}$) symmetry in antiferromagnets has recently emerged as an effective means to induce various features, such as the emergence of Berry curvature, spin-valley locking, magnetoelectric coupling, and the transition from conventional antiferromagnetism to altermagnetism. Conversely, in non-magnetic systems, inversion symmetry breaking in the presence of strong spin-orbit interaction (SOI) gives rise to momentum-dependent spin splitting via the Rashba effect, enabling tunable spin polarization through external electric fields. Motivated by recent advances in two-dimensional materials, we perform first-principles calculations based on density functional theory to investigate the van der Waals (vdW) heterostructure formed by a $\mathcal{P}$-symmetric MnPS$_3$ monolayer and a WS$_2$ monolayer. We demonstrate that the interface hosts a rich interplay of emergent phenomena, including an altermagnetic phase, Rashba spin splitting, spin-valley locking, and valley polarization. Our results demonstrate that the heterostructure exhibits semiconducting behavior with a direct band gap of approximately 1.65~eV and a type-I band alignment. Remarkably, the electronic structure and band alignment can be effectively tuned between type-I and type-II regimes via an external electric field and in-plane biaxial strain. Furthermore, field-induced modulation enables strong control over the altermagnetic phase and the valley splitting. These findings establish the proposed vdW heterostructure as a highly tunable platform with significant potential for spintronic and valleytronic applications.

cond-mat.mtrl-sci↗

arXiv2026

Strain as a topological selector in altermagnetic CrSb

Altermagnetism combines fully compensated magnetic order with a magnetic symmetry that relates inequivalent spin sublattices, offering a promising, still underexplored platform for unconventional topological phases. Here we show that both isotropic tensile strain and electron localization, controlled by an effective Hubbard interaction $U_{\text{eff}}$, can act as efficient and systematic topological control parameters in the altermagnetic Weyl semimetal CrSb. While CrSb hosts Weyl fermions at equilibrium, modest tensile strain of 4-5% stabilizes additional symmetry allowed Dirac crossings and triple-point fermions, with further strain selectively favoring the triple-point phase. We propose a 3D low-energy Hamiltonian that captures the interplay between the Hubbard interaction $U$ and the sublattice symmetry of the altermagnet, giving rise to an interaction-driven Dirac crossing. Our results establish CrSb as a model altermagnet in which either strain or electron localization can selectively access and control the distinct topologies inherent to the altermagnets.

cond-mat.mtrl-sci↗

arXiv2025

Nonsymmorphic symmetry-enforced hourglass fermions and Rashba-Dresselhaus interaction in BiInO$_3$

In this study, we investigate the spin texture of the hourglass fermions band network in BiInO$_3$ using density functional theory (DFT) and symmetry analysis. Hourglass fermions are of interest in spintronics due to their unique and robust band structure, as well as their potential applications in novel electronic devices. BiInO$_3$ exhibits non-symmorphic crystal symmetries, such as glide reflection and glide rotational symmetry, influencing its electronic properties. Through symmetry analysis, we explore the band crossings and spin textures along specific high-symmetry paths in the Brillouin zone. Our results reveal a fascinating hourglass-shaped band dispersion and spin polarisation governed by symmetry operations and spin-orbit interaction. We analyse the spin-splitting mechanisms, including Dresselhaus and Rashba spin-orbit interactions, and suggest potential applications for spin-based devices. This study sheds light on the role of symmetry in crystals for fascinating spin properties of hourglass fermions in non-symmorphic materials, offering insights for future developments in spintronics.

cond-mat.mtrl-sci↗

arXiv2025

Spin-orbit interaction, band topology, and spin texture in BiInO3(001) surface

This research investigates the implication of spin-orbit interaction (SOI) and symmetry on the band topology and spin texture at the (001) surface of BiInO$_3$. Using density functional theory (DFT) and symmetry analysis, the study explores the impact of surface termination on the electronic structure, particularly focusing on how the loss of translational symmetry at the surface influences the band topology of the surface states. Key findings include discovering two dangling surface states (named SS1 and SS2) with distinct spin textures. SS1 exhibits Rashba spin splitting due to surface inversion asymmetry, characterised by isotropic effective mass and tangential spin alignment on constant energy contours. In contrast, SS2 features a persistent spin Texture (PST) spin texture, a momentum-independent spin polarisation. The orbital contributions to these bands, dominated by specific s and p orbitals, dictate the direction and nature of the spin texture. This study highlights BIO's potential as a platform for spintronic applications, where control over spin textures and electronic properties at the surface can enable the design of advanced spin-based devices. The findings bridge the gap between symmetry-driven theoretical frameworks and practical material functionalities, offering insights into the interplay of surface symmetry, SOI, and band topology.

cond-mat.mtrl-sci↗

arXiv2025

Proximity-induced Rashba spin-orbit interaction in BaMnO$_\text{3}|$KTaO$_\text{3}$ heterostructure for antiferromagnetic spintronics

Antiferromagnetic spintronics, a promising technology for ultra-fast electronic devices, faces several challenges, including the lack of materials simultaneously hosting robust antiferromagnetism and adequate Rashba-like interaction. We design a heterostructure of BaMnO$_3|$KTaO$_3$ with the idea of proximity-inducing strong Rashba spin-orbit interaction from KTaO$_3$ part to BaMnO$_3$ part, where the latter is already a robust antiferromagnet. Within our DFT calculations, the heterostructure reveals BaMnO$_3$ bands near the Fermi level with a significant magnetic moment per Mn atom and a decent ordering temperature. Further, the BaMnO$_3$ bands in the heterostructure exhibit linear Rashba interaction with a sizable Rashba coefficient, owing to its proximity to KTaO$_3$. Our work can motivate future research by demonstrating the road map to proximity-induced Rashba interaction for antiferromagnetic spintronics.

cond-mat.mtrl-sci↗

arXiv2025

Mapping Rashba and Dresselhaus spin-orbit interactions to inversion asymmetry in perovskite oxide heterostructures

Inversion asymmetry, combined with spin-orbit interaction, leads to Rashba or Dresselhaus effects, or combinations of them that are promising for technologies based on antiferromagnetic spintronics. Since understanding the exact nature of spin-orbit interaction is crucial for developing a technology based on it, mapping the nature of inversion asymmetry with the type of spin-orbit interaction becomes the key. We simulate a perovskite oxide heterostructure LaAlO$_3|$SrIrO$_3|$SrTiO$_3$ preserving the inversion symmetry within density functional theory to demonstrate the relation between the nature of inversion asymmetry and the corresponding Rashba or Dresselhaus-type interaction. With progressive distortion in the heterostructure, we find how the structure inversion asymmetry sets in with distorted bond lengths and bond angles, leading to Rashba effect in the system. Further, introduction of tilted IrO$_6$ octahedra leads to bulk inversion asymmetry, helping a combined Rashba-Dresselhaus interaction to set in. A comparison of the spin textures obtained from our DFT calculations and theoretical modeling helps us identify the exact nature of the interactions. Besides demonstrating the connection between the nature of asymmetry with Rashba and Dresselhaus interactions, our work may serve as a guide to identifying different types of Rashba-like spin-orbit interactions.

cond-mat.mtrl-sci↗

arXiv2025

Altermagnetic spin splitting and symmetry-enforced partial spin degeneracy in hexagonal MnTe

Besides hosting several intriguing physical properties, the recently discovered time-reversal-asymmetric antiferromagnets, known as altermagnets, hold immense promise for technologies based on spintronics. Understanding the symmetry conditions leading to the spin-splitting becomes the key to further progress in the field. Hexagonal MnTe emerges as an even-parity magnet within the altermagnet family. In this work, using ab initio density functional theory (DFT) within a combination of an appropriate exchange-correlation functional and the relevant corrections, we uncover the spin-splitting features of MnTe. Our calculations reveal the spin degeneracy to be preserved in the $k_z = 0$ and $k_y = 0$ planes, while spin-splitting is observed everywhere else in the Brillouin zone, except the nodal lines identified here. To explain these findings, we provide a comprehensive symmetry analysis based on magnetic space group theory and introduce an insightful symmetry-adapted model Hamiltonian that qualitatively describes the spin-splitting behavior in different parts of the Brillouin zone. Our calculations considering spin-orbit interaction reveal no weak ferromagnetism in MnTe. Nevertheless, we discuss plausible explanations for weak ferromagnetism and anomalous Hall effect reported from experiments. Our comprehensive analysis of the magnetic space group symmetry and the DFT results leads to a thorough understanding of altermagnetism in MnTe, paving the way for possible future technology.

cond-mat.mtrl-sci↗

arXiv2025

Anomalous Hall effect in highly c-plane oriented Mn$_{3}$Ge/Si(100) thin films grown by pulsed laser deposition

Antiferromagnetic Mn$_{3}$Ge with a non-collinear Kagome structures present exciting prospects for exploring Berry curvature driven anomalous Hall effects (AHE). Despite substantial progress in bulk systems, the synthesis of crystalline thin films directly on silicon with a hexagonal phase presents a particular challenge unless a buffer layer is employed. In this study, we report the synthesis of single phase c-plane oriented hexagonal Mn$_{3}$Ge(0001) films on Si(100) using pulsed laser deposition. Under suitable growth conditions, we obtain layer-by-layer films with atomically flat surfaces and interfaces. High-resolution scanning tunneling microscopy study reveals the detail surface atomic structures, where the surface Mn atoms spontaneously arrange into a Kagome lattice. Tunneling spectroscopy (dI/dV) measurement on the atomically resolved Kagome surface show a minima in local density of states near the Fermi level, likely originated from the Weyl crossings near K points. Despite the nearly vanishing magnetization, magnetotransport measurements in 30 nm $Mn_{3}$Ge(0001) films show anomalous Hall resistivity up to 0.41 ($μΩ\cdot\text{cm}$) at 2 K. Our \textit{ab initio} calculations shed further light on the existence of topological features and the band structures in Mn$_{3+x}$Ge$_{1-x}$ with increasing Mn concentration $x$. The anomalous Hall response at room temperature in crystalline Mn$_{3}$Ge films on Si(100) offer promising potential for the development of antiferromagnetic spintronics.

cond-mat.mes-hall↗

arXiv2025

Altermagnetism in orthorhombic $Pnma$ structure through group theory and DFT calculations

Antiferromagnetism, initially considered interesting but useless, recently emerged as one of the most promising magnetic phases for technology. Recently, a low symmetry antiferromagnetic phase, known as altermagnetic phase, have been discovered, where no time reversal ($\mathcal{T}$) symmetry is observed in spite of a vanishing net magnetization, leading to non-degenerate bands from the opposite magnetic sublattices. In this work, we consider two representatives of orthorhombic $Pnma$ space group, namely, BiFeO$_3$ and CaMnO$_3$ and find altermagnetic lowest energy phase in both from our density functional theory calculations. We find a substantial spin-splitting in both systems along a high-symmetry path in the Brillouin zone without considering the spin-orbit interaction (SOI). Detailed features of the band dispersion obtained from our calculation confirm the lifting of sublattice spin degeneracy only in the $k_y$-$k_z$ plane while preserving the spin degeneracy in the other planes of the Brillouin zone. We provide a comprehensive symmetry analysis based on the magnetic space group (MSG) to explain our DFT findings and an insightful symmetry-allowed model Hamiltonian, which qualitatively agrees with our results. Additionally, we extend our symmetry analysis to encompass two other potential MSGs within the $Pnma$ space group that may host the spin-splitting phenomenon without considering SOI and the likely form of their Hamiltonian. These detailed studies pave the way for a deeper understanding of the spin-splitting phenomena within the $Pnma$ space group, offering insights into the intricate interplay between symmetry and electronic as well as magnetic properties.

cond-mat.mtrl-sci↗

arXiv2024

Unsupervised Deep Neural Network Approach To Solve Bosonic Systems

The simulation of quantum many-body systems poses a significant challenge in physics due to the exponential scaling of Hilbert space with the number of particles. Traditional methods often struggle with large system sizes and frustrated lattices. In this research article, we present a novel algorithm that leverages the power of deep neural networks combined with Markov Chain Monte Carlo simulation to address these limitations. Our method introduces a neural network architecture specifically designed to represent bosonic quantum states on a 1D lattice chain. We successfully achieve the ground state of the Bose-Hubbard model, demonstrating the superiority of the adaptive momentum optimizer for convergence speed and stability. Notably, our approach offers flexibility in simulating various lattice geometries and potentially larger system sizes, making it a valuable tool for exploring complex quantum phenomena. This work represents a substantial advancement in the field of quantum simulation, opening new possibilities for investigating previously challenging systems.

cond-mat.mtrl-sci↗

arXiv2024

Unsupervised Deep Neural Network Approach To Solve Fermionic Systems

Solving the Schrödinger equation for interacting many-body quantum systems faces computational challenges due to exponential scaling with system size. This complexity limits the study of important phenomena in materials science and physics. We develop an Artificial Neural Network (ANN)-driven algorithm to simulate fermionic systems on lattices. Our method uses Pauli matrices to represent quantum states, incorporates Markov Chain Monte Carlo sampling, and leverages an adaptive momentum optimizer. We demonstrate the algorithm's accuracy by simulating the Heisenberg Hamiltonian on a one-dimensional lattice, achieving results with an error in the order of $10^{-4}$ compared to exact diagonalization. Furthermore, we successfully model a magnetic phase transition in a two-dimensional lattice under an applied magnetic field. Importantly, our approach avoids the sign problem common to traditional Fermionic Monte Carlo methods, enabling the investigation of frustrated systems. This work demonstrates the potential of ANN-based algorithms for efficient simulation of complex quantum systems, opening avenues for discoveries in condensed matter physics and materials science.

cond-mat.mtrl-sci↗

arXiv2023

Antiferromagnetism, spin splitting, and spin-orbit interaction in MnTe

Hexagonal MnTe emerges as a critical component in designing magnetic quantum heterostructures, calling for a detailed study. After finding a suitable combination of exchange-correlation functional and corrections, our study within {\em ab initio} density functional theory uncovers an insulating state with a preferred antiferromagnetic order. We compute the exchange interaction strengths to estimate the antiferromagnetic ordering temperature via Monte Carlo calculations. Our calculations and symmetry analysis reveal a large spin splitting in the system due to the antiferromagnetic order without considering spin-orbit interaction, except in the $k_x$-$k_y$ plane. Critically examining the band dispersion and spin textures obtained from our calculations and comparing them with an insightful symmetry analysis and analytical model, we confirm a combined Rashba-Dresselhaus interaction in the $k_x$-$k_y$ plane, around the K point of the system. Finally, we find ferroelectricity in the system for a higher energy magnetic configuration. Our results and insights would help design heterostructures of MnTe for technological applications.

cond-mat.mtrl-sci↗

arXiv2022

Rashba-like spin-orbit interaction and spin texture at the KTaO$_\text{3}$ (001) surface from DFT calculations

Rashba-like spin-orbit interaction at oxide heterostructures emerges as a much sought-after feature in the context of oxide spintronics and spin-orbitronics. KTaO$_3$ (KTO) is one of the best substrates available for the purpose, owing to its strong spin-orbit interaction and alternating $+1|-1$ charged layers along the (001) direction. Employing first-principles calculations within density functional theory (DFT) and proposing a possible electrostatic model for charge transfer to the surfaces of KTO slabs, we comprehensively analyze Rashba-like spin-orbit interaction with the help of three-dimensional band dispersion, isoenergetic contours, and projected spin textures $-$ all directly obtained from our DFT results $-$ in a thin insulating slab and a conducting thick slab of KTO. Our results reveal reasonably strong linear Rashba interaction with no signature of Dresselhaus or higher order Rashba interactions in the systems considered here. The rigorous analysis presented here may be crucial for future developments in oxide spintronics.

cond-mat.mtrl-sci↗

arXiv2022

Implications of electron and hole doping on the magnetic properties of spin-orbit entangled Ca$_\text{4}$IrO$_\text{6}$ from DFT calculations

We investigate the electronic structure and magnetic properties of a $J_\text{eff} = 1/2$ iridate Ca$_4$IrO$_6$ and the implications of doping electrons and holes using ab initio density functional theory. Our calculations considering spin-orbit interaction reveal that although the Mott-insulating parent compound transforms into a conductor upon doping, antiferromagnetism sustains in the doped system, albeit with a grossly noncollinear arrangement of the spins. We find a strong spin-orbit interaction and magneto-crystalline anisotropy, causing frustration in the system, possibly leading to the highly noncollinear arrangement of spins upon non-magnetic doping. Our results may be important from the viewpoint of spintronics using iridates or other $5d$ materials.

cond-mat.str-el↗

arXiv2020

Perovskite oxide heterojunction for Rashba-Dresselhaus assisted antiferromagnetic spintronics

A major impediment towards realizing technologies based on the emerging principles of antiferromagnetic spintronics is the shortage of suitable materials. In this paper, we propose a design of polar|nonpolar heterostructures of perovskite oxides, where a single unit cell of SrIrO3 is sandwiched between a thin film of LaAlO3 and a substrate of SrTiO3. Our calculations within the framework of density-functional theory + Hubbard U + spin-orbit coupling reveal a two-dimensional conducting layer with electron and hole pockets at the interface, exhibiting a strong anisotropic Rashba-Dresselhaus effect along with noncollinear antiferromagnetism, indicating the possibility of realizing a spin-orbit torque. An insightful physical model for the anisotropic Rashba-Dresselhaus effect nicely interprets our results, providing an estimate for the Rashba-Dresselhaus coefficients and illustrating pseudospin orientation.We also observe a proximity-induced prominent Rashba-like effect for Ti 3d empty bands. Our results suggest that the heterostructure may possess the essential ingredients for antiferromagnetic spintronics, deserving experimental verification.

cond-mat.mtrl-sci↗

arXiv2019

DFT study of itinerant ferromagnetism in $p$-doped monolayers of MoS$_2$

We use density functional theory to explore the possibility of making the semiconducting transition-metal dichalcogenide MoS$_2$ ferromagnetic by introducing holes into the narrow Mo $d$ band that forms the top of the valence band. In the single impurity limit, the repulsive Coulomb potential of an acceptor atom and intervalley scattering lead to a twofold orbitally degenerate effective-mass like $e'$ state being formed from Mo $d_{x^2-y^2}$ and $d_{xy}$ states, bound to the K and K$'$ valence band maxima. It also leads to a singly degenerate $a'_1$ state with Mo $d_{3z^2-r^2}$ character bound to the slightly lower lying valence band maximum at $Γ$. Within the accuracy of our calculations, these $e'$ and $a'_1$ states are degenerate for MoS$_2$ and accommodate the hole that polarizes fully in the local spin density approximation in the impurity limit. With spin-orbit coupling included, we find a single ion magnetic anisotropy of $\sim 5\,$meV favouring out-of-plane orientation of the magnetic moment. Pairs of such hole states introduced by V, Nb or Ta doping are found to couple ferromagnetically unless the dopant atoms are too close in which case the magnetic moments are quenched by the formation of spin singlets. Combining these exchange interactions with Monte Carlo calculations allows us to estimate ordering temperatures as a function of the dopant concentration $x$. For $x \sim 9\%$, Curie temperatures as high as 100K for Nb and Ta and in excess of 160K for V doping are predicted. Factors limiting the ordering temperature are identified and suggestions made to circumvent these limitations.

cond-mat.mtrl-sci↗

arXiv2019

Itinerant Ferromagnetism in p-doped Monolayers of MoS2

Density functional theory is used to explore the possibility of inducing impurity band ferromagnetism in monolayers of semiconducting MoS2 by introducing holes into the narrow Mo 4d band that forms the top of the valence band. A large out of plane anisotropy is found for unpaired spins bound to the substitutional acceptor impurities V, Nb and Ta that couple ferromagnetically for all but the shortest separations. Using the separation dependent exchange interactions as input to Monte Carlo calculations, we estimate ordering temperatures as a function of the impurity concentration. For about 9% of V impurities, Curie temperatures in excess of 160 K are predicted. The singlet formation at short separations that limits the ordering temperature is explained and we suggest how it can be circumvented.

cond-mat.mtrl-sci↗

arXiv2018

Enhancement of the superconducting transition temperature by Re doping in Weyl semimetal MoTe$_{2}$

This work presents the emergence of superconductivity in Re substituted topological Weyl semimetal MoTe$_{2}$. Re substitution for Mo sites lead to a sizable enhancement in the superconducting transition temperature (T$_{c}$). A record high T$_{c}$ at ambient pressure in a 1T$'$-MoTe$_{2}$ (room temperature structure) related sample is observed for the Mo$_{0.7}$Re$_{0.3}$Te$_{2}$ composition (T$_{c}$ = 4.1 K, in comparison MoTe$_{2}$, shows a T$_{c}$ of 0.1 K). The experimental and theoretical studies indicate that Re substitution is doping electrons and facilitates the emergence of superconductivity by enhancing the electron-phonon coupling and density of states at the Fermi level. Our findings, therefore, open a new way to further manipulate and enhance the superconducting state together with the topological states in 2D van der Waals materials.

cond-mat.supr-con↗