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Subhradip Ghosh

Publications and source records attributed to Subhradip Ghosh.

At least 19 recordsLinked to original sources
arXiv2026

Interplay of Valley, Orbital, Spin, and Layer Degrees of Freedom in Ta$_2$CS$_2$ MXene

We show that the MXene Ta$_2$CS$_2$ provides an excellent platform for hosting multiple coupled degrees of freedom, viz., valley, spin, orbital, and layer. The interplay among these degrees of freedom gives rise to a range of intriguing properties in reciprocal space, including valley-orbital and orbital-layer coupling. In the presence of spin-orbit interaction, these couplings lead to valley-dependent and layer-dependent spin splitting of the electronic bands. We further show that the intrinsic electric polarization in Ta$_2$CS$_2$ introduces an additional tuning parameter, enabling control over these coupled degrees of freedom and resulting in switchable valley-dependent orbital moments and Zeeman-like spin splitting. We demonstrate that these nontrivial orbital and spin textures manifest in the orbital and spin Hall effects, respectively. Our results establish noncentrosymmetric MXenes as a promising platform for exploring the interplay among multiple degrees of freedom, their tunability, and the resulting orbital and spin transport phenomena in these two-dimensional materials, thereby paving the way for next-generation spin-orbitronic devices.

cond-mat.str-el↗
arXiv2025

Acoustic phonon-restricted four-phonon interactions: Impact on thermal and thermoelectric transport in monolayer h-NbN

To explore the thermal and thermoelectric potential of 2D materials, we study the h-NbN monolayer, which lacks mirror symmetry and features a large acoustic-optical phonon gap and quadratic flexural mode. First-principles calculations and the Boltzmann transport formalism reveal a complex interplay of multi-phonon scattering processes, where flexural phonons and four-phonon interactions play a significant role in heat transport, primarily dominated by acoustic phonons. Notably, the four-phonon interactions are predominantly confined to acoustic phonons. Tensile strain preserves the underlying scattering mechanisms while reducing anharmonicity, consequently, the scattering rates, enhancing thermal conduction. Simultaneously, competing modifications in thermal and electrical transport shape the strain-dependent thermoelectric response, achieving a figure of merit approaching 1 at elevated temperatures, a testament to its thermoelectric promise. Our findings underscore the critical role of microscopic transport modeling in accurately capturing thermal and thermoelectric properties, paving the way for advanced applications of 2D materials.

cond-mat.mtrl-sci↗
arXiv2024

Consequences of magneto-electrical coupling in multiferroic VSe$_{2}$$/$Sc$_{2}$CO$_{2}$ heterostructures

Two-dimensional van der Waals heterostructures are potential game changers both in understanding the fundamental physics and in the realization of various devices that exploit magnetism at the nanoscale. Multiferroic heterostructures comprising a two-dimensional ferroelectric and a two-dimensional ferromagnet are ideal candidates for electrical control of properties of the ferromagnets that can lead to non-volatile memory devices, for example. Relatively new but immensely promising two-dimensional materials, MXene and transition metal dichalcogenides, can be effectively combined to achieve the goal as both have flexibilities in their structures and compositions that are tunable. In this work, using Density Functional Theory, we have investigated the magneto-electric coupling driven transitions in the electronic ground states of VSe$_{2}$-Sc$_{2}$CO$_{2}$ bi-layer and tri-layer heterostructures. Our results demonstrate that the change in the ferroelectric polarisation in the MXene layer leads to changes in the spin-polarized band structures of the magnetic component VSe$_{2}$ enabling a semiconductor to half-metal transition in these heterostructures. We propose several applications of this magneto-electric coupling in these multiferroic heterostructures that can lead to the efficient operation of Field Effect transistors and achieve non-volatility in memory devices at the nanoscale.

cond-mat.mtrl-sci↗
arXiv2024

Sensing food quality by silicene nanosheets : a Density Functional Theory study

Volatile organic compounds (VOCs) emitted by food products are considered markers for assessing quality of food. In this work, first-principles Density Functional Theory (DFT) and Non-equilibrium Green's function (NEGF) methods have been employed to model chemo-resistive gas sensor based on two-dimensional silicene based nanosheets that can sense the six different VOCs emitted by standard food products. Our calculations with unpassivated and flourine passivated silicene(F-silicene) sheets as sensor materials show that flourine passivated silicene has significantly better sensitivity towards all six VOC molecules (Acetone, Dimethylsulfide, Ethanol, Methanol, Methylacetate and Toluene). Moreover, flourinated silicene sensor is found to be capable of separately recognising four VOCs, a much better performance than r-GO used in a recent experiment. We analyse the microscopic picture influencing sensing capabilities of un-passivated and fluorinated silicene from the perspectives of adsorption energy, charge transfer and changes in the electronic structure. We find that better sensing ability of fluorinated silicene nanosheet can be correlated with the changes in the electronic structures near the Fermi level upon adsorption of different VOCs. The results imply that passivated silicene can work better as a sensor than r-GO in case of generic food VOCs. The results are important since modelling of various two-dimensional nano-sensors can be done in the similar way for detection of more complex VOCs emitted by specific food products.

cond-mat.mes-hall↗
arXiv2024

Tunable magnetism in Nitride MXenes:consequences of atomic layer stacking

We have performed Density Functional Theory (DFT) based calculations to investigate the effects of stacking patterns on the electronic and magnetic properties of several Nitride MXenes. MXenes, a relatively new addition to the family of two-dimensional materials, have exhibited fascinating properties on several occasions, primarily due to their compositional flexibility. However, compared to Carbide MXenes, Nitride MXenes are much less explored. Moreover, the structural aspects of MXenes and the tunability it may offer have not been explored until recently. In this work, we have combined these two less-explored aspects to examine the structure-property relations in the field of magnetism. We find that in the family of M$_{2}$NT$_{2}$ (M=Sc, Ti, V, Cr, Mn; T=O, F) MXenes, the stacking of transition metal planes has a substantial effect on the ground state and finite temperature magnetic properties. We also find that the electronic ground states can be tuned by changing the stacking pattern in these compounds, making the materials appropriate for applications as magnetic devices. Through a detailed analysis, we have connected the unconventional stacking pattern-driven tunability of these compounds with regard to electronic and magnetic properties to the local symmetry, inhomogeneity (or lack of it) of structural parameters, and electronic structures.

cond-mat.mtrl-sci↗
arXiv2024

Performance Parameters of Infra-red and Visible-active MXene Photocatalysts for Water Splitting

Water splitting reactions through photocatalysis is an efficient and sustainable technique for the generation of green energy. The photocatalyst's ability to effect simultaneous generation of hydrogen and oxygen, along with efficiency in utilisation of charged carriers, conversion of solar energy to hydrogen, fast migration, and low recombination rates of carriers, are the parameters to decide its suitability in water splitting. In literature, comprehensive calculation and analysis of all these performance parameters for a potential photocatalyst are rare. In this work, we have performed first-principles-based computations to find new efficient photocatalysts from the family of Janus MXenes and assessed their performance parameters. Strain engineering has been invoked in search of new materials. Out of 14 studied materials, we find 5 materials: Sc$_{2}$COS, Zr$_{2}$COS, Hf$_{2}$COS, and ZrHfCO$_{2}$ under zero or finite tensile strain and Hf$_{2}$COSe at 6\% tensile strain meeting the requirements of simultaneous reactions to split water. The computations of various efficiency-related parameters demonstrate that Zr$_{2}$COS, Hf$_{2}$COS, and Hf$_{2}$COSe have excellent efficiencies, significantly better than the well-known photocatalysts. The origin of such performances lies in their electronic and optical properties, which are analysed systematically.

cond-mat.mtrl-sci↗
arXiv2024

Computational Study Based Prediction of New Photocatalysts for water splitting by systematic manipulation of MXene surfaces

The compositional and structural flexibility of functionalised two-dimensional metal carbonitrides or MXenes has been exploited through a combinatorial search for new materials that can act as catalysts for photo-assisted water splitting by absorbing sunlight with energy in the infra-red region. Detailed calculations on 49 Janus MXenes where two surfaces are of asymmetric nature are carried out by first-principles Density Functional Theory. A screening procedure is adopted to arrive at potential candidates. Our calculations predict four new materials whose surfaces can activate both hydrogen and oxygen evolution reactions upon splitting water, two out of which are infra-red active, and the rest are visible light-active. We have performed a detailed microscopic analysis to find out the interrelations of the structural model of surface functionalisation, the chemistry of the surfaces, the electronic structure, and the alignment of bands with respect to the reaction potentials that explain our results. Apart from these four compounds, we find thirteen other compounds that are suitable for either hydrogen evolution or oxygen reduction reactions. This study lays out a guideline for the systematic discovery of potential new catalysts for water splitting under sunlight irradiation.

cond-mat.mtrl-sci↗
arXiv2024

Strain aided drastic reduction in lattice thermal conductivity and improved thermoelectric properties in Janus MXenes

Surface and strain engineering are among the cheaper ways to modulate structure property relations in materials. Due to their compositional flexibilities, MXenes, the family of two-dimensional materials, provide enough opportunity for surface engineering. In this work, we have explored the possibility of improving thermoelectric efficiency of MXenes through these routes. The Janus MXenes obtained by modifications of the transition metal constituents and the functional groups passivating their surfaces are considered as surface engineered materials on which bi-axial strain is applied in a systematic way. We find that in the three Janus compounds Zr$_{2}$COS, ZrHfO$_{2}$ and ZrHfCOS, tensile strain modifies the electronic and lattice thermoelectric parameters such that the thermoelectric efficiency can be maximised. A remarkable reduction in the lattice thermal conductivity due to increased anharmonicity and elevation in Seebeck coefficient are obtained by application of moderate tensile strain. With the help of first-principles electronic structure method and semi-classical Boltzmann transport theory we analyse the interplay of structural parameters, electronic and dynamical properties to understand the effects of strain and surface modifications on thermoelectric properties of these systems. Our detailed calculations and in depth analysis lead not only to the microscopic understanding of the influences of surface and strain engineering in these three systems, but also provide enough insights for adopting this approach and improve thermoelectric efficiencies in similar systems.

cond-mat.mtrl-sci↗
arXiv2024

In-plane ordering and tunable magnetism in Cr-based MXenes

MXene, the two-dimensional derivatives of MAX compounds, due to their structural and compositional flexibility, is an ideal family of compounds to study a number of structure-property relations. In this work, we have investigated the tunability of magnetic properties in Cr-based MXenes that have an in-plane ordering arising out of alloying Cr with another non-magnetic transition metal atom. Using Density Functional Theory based calculations we have explored the effects of composition and surface functionalisations on the electronic and magnetic properties of these in-plane ordered MXenes known as i-MXenes. We found that the electronic and magnetic ground states are quite sensitive to the structure and composition. This provides enough tunability in these compounds so that they can be used for practical applications. Our calculated results of magnetic transition temperatures and magnetic anisotropy energies are comparable to many a established two-dimensional magnets. These put together widen the prospect of these i-MXenes for multiple usage as magnetic devices making them attractive for further investigation.

cond-mat.mtrl-sci↗
arXiv2024

Symmetry Lowering Through Surface Engineering and Improved Thermoelectric Properties in MXenes

Despite ample evidence of their influences on the transport properties of two-dimensional solids, the interrelations of reduced symmetry, electronic and thermal transport, have rarely being discussed in the context of thermoelectric materials. With the motivation to design new thermoelectric materials with improved properties, we have addressed these by performing first-principles Density Functional Theory based calculations in conjunction with semi-classical Boltzmann transport theory on a number of compounds in the MXene family. The symmetry lowering in parent M$_{2}$CO$_{2}$ MXenes are done by replacing transition metal $M$ on one surface, resulting in Janus compounds MM$^{\prime}$CO$_{2}$. Our calculations show that the thermoelectric figure-of-merit can be improved significantly by such surface engineering. We discuss in detail, both qualitatively and quantitatively, the origin behind high thermoelectric parameters for these compounds. Our in-depth analysis shows that the modifications in the electronic band structures and degree of anharmonicity driven by the dispersions in the bond strengths due to lowering of symmetry, an artefact of surface engineering, are the factors behind the trends in the thermoelectric parameters of the MXenes considered. The results also substantiate that the compositional flexibility offered by the MXene family of compounds can generate complex interplay of symmetry, electronic structure, bond strengths and anharmonicity which can be exploited to engineer thermoelectric materials with improved properties.

cond-mat.mtrl-sci↗
arXiv2023

Improved charge storage capacity of supercapacitor electrodes by engineering surfaces: the case of Janus MXenes

Surface Engineering in two-dimensional(2D) materials has turned out to be an useful technique to improve their functional properties. By designing Janus compounds MM$^{\prime}$C in MXene family of compounds M$_{2}$C where the two surfaces are constituted by two different transition metal M and M$^{\prime}$, we have explored their potentials as electrodes in a supercapacitor with acidic electrolyte. Using Density functional Theory (DFT) \cite{dft} in conjunction with classical solvation model we have made an in depth analysis of the electrochemical parameters of three Janus MXenes, passivated by oxygen - NbVC, MnVC and CrMnC. Comparisons with the corresponding end point MXenes Nb$_{2}$C, V$_{2}$C, Mn$_{2}$C and Cr$_{2}$C are also made. We find that the surface redox activity enhances due to formation of Janus, improving the charge storage capacities of MXene electrodes significantly. Our analysis reveals that the improved functionality has its root in the variations in the charge state of one of the constituents in the Janus compound which, in turn, has its origin in the electronic structure changes due to the surface manipulation. Our work, which is the first on the electrochemical properties of Janus MXenes for supercapacitor applications, suggests the surface engineering by forming appropriate Janus compounds as a possible route to extract high power density in a MXene electrode-acidic electrolyte based energy storage devices.

cond-mat.mtrl-sci↗
arXiv2023

Effects of Chemical and magnetic disorder on the electrochemical properties of V$_{2-x}$Mn$_{x}$CO$_{2}$} MXene electrodes

Investigation of structure-property relations in chemically and magnetically disordered materials can give rise to interesting physical phenomena. The potential of two-dimensional MXenes as electrodes in supercapacitor applications have been studied extensively. However, the role of chemical and magnetic disorder on their electrochemical parameters like the capacitance have not been explored yet. In this work, we have systematically addressed this for V$_{2-x}$Mn$_{x}$CO$_{2}$ MXene solid solutions with an analysis based upon results from first-principles electronic structure calculations. We find that the variations in the total capacitance over a voltage window depends upon the degree of chemical and magnetic disorder. In course of our investigation, we also found out that the magnetic structure on the surface can substantially influence the redox charge transfer, an yet unexplored phenomenon. A significantly large charge transfer and thus a large capacitance can be obtained by manipulating the chemical composition and the magnetic order of the surfaces.These findings can be useful in designing operational supercapacitor electrodes with magnetic constituents.

cond-mat.mtrl-sci↗
arXiv2022

Stacking and Layer dependence of magnetic properties in Ti\textsubscript{2}C and Fe\textsubscript{2}C

Magnetic MXenes are turning out to be an important family of materials for exploring 2D magnetism. However, investigations into the inter-dependence of layer thickness, stacking patterns and magnetism in these materials, from a microscopic point of view, is still lacking. In this work, we have used Density Functional Theory (DFT) based calculations to understand the effects of layer thickness and stacking on the magnetic properties in two magnetic MXenes, Ti$_{2}$C and Fe$_{2}$C in their monolayer and bilayer forms. The ground state magnetic structures, magnetic moments, magnetic exchange interactions, magnetic transition temperatures and magnetic anisotropy energies are calculated and analysed using their electronic structures and standardised models. We find that in both systems increase in layer thickness (monolayer to bilayer) affects the ground state magnetic configuration which is driven by the changes in the magnetic exchange interactions. While the effects of stacking pattern is rather weak in Ti$_{2}$C, they are substantial, both qualitatively and quantitatively in Fe$_{2}$C. The computed results are analysed from their electronic structures. The results suggest that fascinating physical effects can be obtained in Fe$_{2}$C by tuning the layer thickness and stacking patterns, making it more suitable for device applications.

cond-mat.mtrl-sci↗
arXiv2022

Computational studies on electrochemical performances of doped and substituted $Ti_3C_2O_2$ MXene

Using Density functional theory (DFT) in conjunction with a solvation model we have investigated the phenomenon of eletrode-electrolyte interaction at the electrode surface and its consequences on the electrochemical properties like the charge storage and total capacitance of doped and substituted oxygen functionalised Ti$_{3}$C$_{2}$ supercapcitor electrode. We have studied nitrogen doped, nitrogen substituted and molybdenum substituted Mxenes in acidic electrolyte H$_{2}$SO$_{4}$ solution. By considering nitrogen doping at different sites, we found that the greatest capacitance is obtained for doping at functional sites. Our results agree well with the available experiment. We also found that the enhancement in capacitances due to nitrogen doping is due to amplifications in the pseudocapcitances. We propose that the primary mechanism leading to the enhanced value of the capacitances due to nitrogen doping is surface redox activity. The performances for substituted systems, on the other hand, are degraded in comparison to the pristine ones. This suggests that better storage capacities in Ti$_3$C$_{2}$O$_{2}$ electrode can be obtained by doping only. We provide insights into the reasons behind contrasting behaviour in doped and substituted systems and suggest ways to further improve the capacitances in doped system.

cond-mat.mtrl-sci↗
arXiv2021

Systematic investigation of capacitances in functionalized MXene supercapacitors $M_{n+1}C_nO_2$, $M=Ti,V,Nb,Mo$

MXene, the class of two-dimensional materials, has been found to be useful as potential electrode materials for electrochemical capacitors. Although experimental investigation on the electrochemical performances of a few MXenes have been carried out with exciting results, a complete understanding of their atomic scale behaviour is yet to be done. Using first-principles electronic structure methods, we perform a systematic investigation of the capacitances in pristine and functionalised MXenes $M_{n+1}C_{n}O_{2}$ where $M=Ti,V,Nb$ and $Mo$. We provide results on each of the three sources of the capacitance and analyse them in detail for a complete understanding of their behaviour. The interpretation of the experimental results, wherever available, in the light of our computations,provides useful insights.

cond-mat.mtrl-sci↗
arXiv2020

Giant magnetocaloric effect driven by first-order magneto-structural transition in cosubstituted Ni-Mn-Sb Heusler compounds: predictions from \textit{Ab initio} and Monte Carlo calculations

Using Density Functional Theory and a thermodynamic model [Physical Review B 86, 134418 (2012)], in this paper, we provide an approach to systematically screen compounds of a given Heusler family to predict ones that can yield giant magnetocaloric effect driven by a first-order magneto-structural transition. We apply this approach to two Heusler series Ni$_{2-x}$Fe$_{x}$Mn$_{1+z-y}$Cu$_{y}$Sb$_{1-z}$ and Ni$_{2-x}$Co$_{x}$Mn$_{1+z-y}$Cu$_{y}$Sb$_{1-z}$, obtained by cosubstitution at Ni and Mn sites. We predict four new compounds with potentials to achieve the target properties. Our computations of the thermodynamic parameters, relevant for magnetocaloric applications, show that the improvement in the parameters in the predicted cosubstituted compounds can be as large as four times in comparison to the off-stoichiometric Ni-Mn-Sb and a compound derived by single substitution at the Ni site, where magnetocaloric effects have been observed experimentally. This work establishes a protocol to select new compounds that can exhibit large magnetocaloric effects and demonstrate cosubstitution as a route for more flexible tuneability to achieve outcomes, better than the existing ones.

cond-mat.mtrl-sci↗
arXiv2019

Understanding the origin of the magneto-caloric effects in substitutional Ni-Mn-Sb-Z (Z=Fe, Co, Cu) compounds: insights from first-principles calculations

Ni-Mn based ternary Heusler compounds have drawn attentions lately as significant magneto-caloric effects in some of them have been observed. Substitution of Ni and Mn by other $3d$ transition metals in controlled quantity have turned out to be successful in enhancing the effect and bring the operational temperatures closer to the room temperature. Using density functional theory calculations, in this work, we have systematically explored the roles of various factors such as site occupancies, magnetic interactions, and compositions associated with the constituents of Mn-excess Ni$_{2}$MnSb Heusler compounds upon substitution of Ni and/or Mn by $3d$ transition metals Fe, Co and Cu. Our calculations unveiled the physics behind the variations of physical properties associated with the magneto-caloric effects, and thus interpreted the available experimental results successfully. The work also provided important information on the compounds and the composition ranges where significant magneto-caloric effects may be realised and further experimental investigations need to be done.

cond-mat.mtrl-sci↗
arXiv2018

Half-metallicity in quaternary Heusler alloys with 3$d$ and 4$d$ elements: observations and insights from DFT calculations

In this work, we provide important insights into the evolution of half-metallicity in quaternary Heusler alloys. Employing {\it ab initio} electronic structure methods we study 18 quaternary Heusler compounds having the chemical formula CoX$^\prime$Y$^\prime$Al, where Y$^\prime$ = Mn, Fe; and X$^\prime$ a 4$d$ element. Along with the search for new materials for spintronics applications, the trends in structural, electronic, magnetic properties and Curie temperature were investigated. We have made comparative studies with the compounds in the quaternary series CoX$^{\prime}$Y$^{\prime}$Si with X$^{\prime}$ materials from 3$d$ and 4$d$ transition metal series in the periodic table. We observe that the half-metallic behaviour depends primarily on the crystal structure type based on atomic arrangements and the number of valence electrons. As long as these two are identical, the electronic structures and the magnetic exchange interactions bear close resemblances. Consequently, the materials exhibit identical electronic properties, by and large. We analysed the roles of different transition metal atoms in affecting hybridisations and correlated them with the above observations. This work, therefore, provides important perspectives regarding the underlying physics of half-metallic behaviour in quaternary Heusler compounds which goes beyond specifics of a given material. This, thus, paves way for smart prediction of new half-metals. This work also figures out an open problem of understanding how different ternary Heuslers with different electronic behaviour may lead to half-metallic behaviour in quaternary Heuslers with 4$d$ transition metal elements.

cond-mat.mtrl-sci↗