arXiv subjects

Antik Sihi

Publications and source records attributed to Antik Sihi.

15 recordsLinked to original sources

arXiv2026

Self-Consistent Coulomb Interactions from Constrained Dynamical Mean-Field Theory

We develop a self-consistent first-principles framework for determining the screened Coulomb interaction strength (U) based on constrained dynamical mean-field theory (cDMFT). Unlike conventional approaches, this method incorporates essential vertex corrections within the same embedded-DMFT formalism used for the electronic structure calculation. Using the cDMFT-derived interaction strengths as input to embedded DMFT yields spectral functions in excellent agreement with photoemission experiments across a wide range of materials, spanning 3d to 5d transition-metal compounds, including correlated metals, Mott insulators, altermagnets, and unconventional superconductors. This unified many-body framework establishes a systematic first-principles route for determining interaction strengths in correlated materials and substantially enhances the predictive power of DFT+DMFT and its extensions.

cond-mat.str-el↗

arXiv2026

Systematic dynamical mean-field theory study of 3d perovskite oxides with uniform Coulomb interactions

Strongly correlated transition-metal perovskite oxides pose a fundamental challenge for electronic-structure theory and for large-scale, data-driven materials discovery. While DFT+DMFT provides a quantitatively accurate description of such systems, its high-throughput application is hindered by the need to determine material-specific Coulomb interaction parameters ($U$). First-principles approaches such as the cRPA predict a highly nonlinear and non-transferable evolution of the interaction strength across chemically similar ABO$_3$ perovskites. Here we show that this paradigm does not extend to the large-energy-window eDMFT, which employs highly localized orbitals and treats electronic correlations and screening self-consistently within the same many-body framework. As a result, spectral properties are governed primarily by the dynamical self-energy rather than by static interaction-induced energy shifts. Recent constrained-eDMFT calculations demonstrated that, for broad classes of $3d$ transition-metal oxides, the self-consistently screened Coulomb interactions naturally fall within relatively narrow ranges for correlated metals and insulators. Motivated by these findings, we implement a high-throughput eDMFT framework employing physically derived interaction values of $U=6$ eV for metals and $U=10$ eV for insulators together with $exact$ double counting. We test this framework using systematic high-throughput eDMFT calculations for ABO$_3$ compounds (A = Ca, Sr, La; B = V--Ni) and benchmark the resulting spectral functions against photoemission experiments, where we find overall excellent agreement. Our results establish that charge self-consistent eDMFT enables robust, parameter-tuning-free high-throughput many-body calculations for correlated oxides, opening a practical pathway toward predictive electronic-structure databases for strongly correlated materials.

cond-mat.str-el↗

arXiv2025

Correlation Enhanced Electron-Phonon Coupling in FeSe/SrTiO$_3$ at a Magic Angle

While a predictive theory for unconventional superconductivity in Fe-based superconductors remains elusive, an extensively debated aspect is the interaction between phonons and strongly correlated electrons, and its potential role in the pairing mechanism. Here, through the combination of first principles dynamical mean field theory calculations and epitaxial growth of the single-layer FeX (X=Se, S, Te) on SrTiO$_3$ (STO)(001) substrate, which facilitates the controlled distortion of the FeX$_4$ tetrahedron, we demonstrate an unique superconducting dome where the superconducting gap peaks at a `magic' angle of the FeX$_4$ tetrahedron and the electron-phonon coupling (EPC) for the A$_{1g}$ mode is maximized for the FeSe film. Our findings uncover a significant role of electronic correlations in strengthening Cooper pairing in unconventional superconductors by enhancing EPC.

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arXiv2024

Enhanced Pauli spin response, failure of Stoner \& spin fluctuation models, and presence of 6 $eV$ plasmonic excitations in Ni metal

We revisit the electronic structure of Ni, using the density functional theory (DFT) and dynamical mean-field theory (DMFT) for the theoretical description of its electronic structure properties along with finite-temperature magnetism. Our study provides a comprehensive account of electronic and magnetic properties with the same set of Coulomb interaction parameters, $U$($J$)=5.78(1.1) $eV$ calculated using first-principles approach. The nature of theoretical magnetization curves obtained from DFT \& DFT+DMFT as well as the experimental curve show deviation from the standard models of magnetism, $viz$ Stoner and spin fluctuation model. The temperature dependent DFT approach is found to well describe the finite-temperature M(T) of Ni below critical temperature ($T$ $\leq$ 631 K). The study finds significant Pauli-spin susceptibility contribution to paramagnetic spin susceptibility. Excluding the Pauli-spin response yields a linear Curie-Weiss dependence of the inverse paramagnetic susceptibility at higher temperatures. Also, the presence of mixed valence electronic configuration (3$d^8$, 3$d^9$ and 3$d^7$) is noted. The competing degrees of both the itinerant and localized moment picture of 3$d$ states are found to dictate the finite-temperature magnetization of the system. Furthermore, the quasiparticle scattering rate is found to exhibit strong deviation from $T^2$ behavior in temperature leading to the breakdown of conventional Fermi-liquid theory. In addition to the 6 $eV$ feature, our calculated electronic excitation spectrum confirms the satellite feature extending $\sim$10 $eV$ binding energy, being consistent with experimental observation. Interestingly, our $G_0W_0$ results find the presence of plasmonic excitation contribution to the intensity of famous 6 $eV$ satellite along with the electronic correlation effects,paving way for its reinterpretation.

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arXiv2024

Half-metallic transport and spin-polarized tunneling through the van der Waals ferromagnet Fe${_4}$GeTe$_{2}$

The recent emergence of van der Waals (vdW) ferromagnets has opened new opportunities for designing spintronic devices. We theoretically investigate the coherent spin-dependent transport properties of the vdW ferromagnet Fe$_4$GeTe$_2$, by using density functional theory combined with the non-equilibrium Green's functions method. We find that the conductance in the direction perpendicular to the layers is half-metallic, namely it is entirely spin-polarized, as a result of the material's electronic structure. This characteristic persists from bulk to single layer, even under significant bias voltages, and it is little affected by spin-orbit coupling and electron correlation. Motivated by this observation, we then investigate the tunnel magnetoresistance (TMR) effect in an magnetic tunnel junction, which comprises two Fe$_4$GeTe$_2$ layers separated by the vdW gap acting as insulating barrier. We predict a TMR ratio of almost 500\%, which can be further boosted by increasing the number of Fe$_4$GeTe$_2$ layers in the junction.

cond-mat.mtrl-sci↗

arXiv2022

First-principles evidence of type-II Weyl phonons in rock-salt Tin Chalcogenides (SnS, SnSe & SnTe) materials

Recent studies on different topological materials in condensed matter physics have provided the evidence of topological nature for bosonic particle like phonons by performing various theoretical calculations and experimental observations. Here, the topological behaviours of phonons of SnS, SnSe and SnTe materials in rock-salt structure are investigated using $ab$-$initio$ methodology. For all these materials, the tilted linear band touching is observed along with the presence of band inversion in direction X-W. The topological point in phonon dispersion curve along X-W direction is found to be $\sim$2.83, $\sim$2.46 and $\sim$2.51 THz for SnS, SnSe and SnTe, respectively. The calculated numbers of Weyl points (WPs) is estimated to be 56, 24 and 54 for SnS, SnSe and SnTe, respectively. These WPs have shown conserved Chiral charges for all corresponding materials. The surface local density of states is computed for these compounds, where the surface arc is clearly seen. In case of SnS, the surface arc is found at 2.0 - 2.2 THz energy region. Also, the isofrequency surface states are investigated to observe the presence of Fermi arc for SnX (X = S, Se, Te). The present first-principles calculation predicts that SnS, SnSe and SnTe show type-II Weyl phononic behaviour along with evidence of topological phononic surface states.

cond-mat.mtrl-sci↗

arXiv2022

Evidence of phase stability, topological phonon and temperature-induced topological phase transition in rocksalt SnS and SnSe

Both SnS and SnSe have been experimentally and theoretically confirmed as topological crystalline insulators in native rocksalt structure. Here, phononic structure, thermodynamical properties and temperature dependent electron-phonon interaction (EPI) have investigated for both the materials in rocksalt phase. Previously performed theoretical studies have predicted the phase instability of SnS in this crystal structure at ambient condition. But, after a detailed study performing on the phonon calculation of SnS, we have predicted the phase stability of SnS with considering the Sn 4$p$ orbitals as valence states in $ab-initio$ calculation. The importance of long range Coulomb forces along with the themodynamical properties are also described in detailed for both materials. The preliminary evidence of topological phonon is found along X-W direction, where the linear band touching is observed as compared to type II Weyl phononic material ZnSe. The topological phase transition is seen for these materials due to EPI, where non-linear temperature dependent bandgap is estimated. The predicted value of transition temperature for SnS (SnSe) is found to be $\sim$700 K, where after this temperature the non-trivial to trivial topological phase is seen. The strength of EPI shows more stronger impact on the electronic structure of SnS than SnSe material. The reason of non-linear behaviour of bandgap with rise in temperature is discussed with the help of temperature dependent linewidths and lineshifts of conduction band and valence band due to EPI. The present study reveals the phase stability of SnS along with the comparative study of thermal effect on EPI of SnS and SnSe. Further, the possibility of temperature induced topological phase transition provides one of important behaviour to apply these two materials for device making application.

cond-mat.mtrl-sci↗

arXiv2022

Exploring temperature dependent electron-electron interaction of topological crystalline insulators (SnS and SnSe) within Matsubara-time domain

Both experimental and theoretical studies show non-trivial topological behaviour in native rocksalt phase for SnS and SnSe and categorize these materials in topological crystalline insulators. Here, the detailed electronic structures studies of SnS and SnSe in the rocksalt phase are carried out using many-body $GW$ based theory and density functional theory both for ground states and temperature dependent excited states. The estimated values of fundamental direct bandgaps around L-point using $G_0W_0$ (mBJ) are $\sim$0.27 ($\sim$0.13) eV and $\sim$0.37 ($\sim$0.17) eV for SnS and SnSe, respectively. The strength of hybridization between Sn 5$p$ and S 3$p$ (Se 4$p$) orbitals for SnS (SnSe) shows strong k-dependence. The behaviour of $\overline{W}$ ($ω$), which is the averaged value of diagonal matrix elements of fully screened Coulomb interaction, suggests to use full-$GW$ method for exploring the excited states because the correlation effects within these two materials are relatively weak. The temperature dependent electronic structure calculations for SnS and SnSe provide linearly decreasing behaviour of bandgaps with rise in temperatures. The existence of collective excitation of quasiparticles in form of plasmon is predicted for these compounds, where the estimated values of plasmon frequency are $\sim$9.5 eV and $\sim$9.3 eV for SnS and SnSe, respectively. The imaginary part of self-energy and mass renormalization factor ($Z_\textbf{k}(ω)$) due to electron-electron interaction (EEI) are also calculated along W-L-$Γ$ direction for both the materials. The present comparative study reveals that the behaviour of temperature dependent EEI for SnS and SnSe are the almost same and EEI is important for high temperature transport properties.

cond-mat.str-el↗

arXiv2021

TRACK: A python code for calculating the transport properties of correlated electron systems using Kubo formalism

Exploring the transport properties of different materials brings new avenue for basic understanding of emergent phenomena and practical applications in many different fields. Here, we report a program named as TRACK (TRAnsport properties for Correlated materials using Kubo formalism) which is written in Python 3 for calculating temperature dependent electrical conductivity, electronic part of thermal conductivity, Seebeck coefficient and Lorenz number. In this code, Kubo linear-response formalism is utilized for computing these parameters using both interacting and non-interacting electronic structure methods. The formula for transport coefficients is accordingly modified to obtain the transport parameters under relaxation time approximation using band-theory. The basic inputs of this program are the structural information, dense k-points sampling in the irreducible part of the Brillouin zone and the information of velocity matrix elements, which can be calculated using third-party ab-initio package. TRACK is expected to calculate the transport properties of different class of materials. The code has been benchmarked by performing calculation on three different types of materials namely Vanadium (V), FeSi and LaCoO$_3$, which are metal, semiconductor and Mott insulator, respectively. The temperature dependent behaviour of the transport coefficients for these materials show fairly good agreement with the corresponding experimental data.

cond-mat.str-el↗

arXiv2021

An ab-initio study of topological and transport properties of YAuPb

In the last few decades, the study of topological materials has been carried out on an extensive scale. Half-Heusler alloys are well known for their topological behaviours. In this work, we present a detailed study of topological properties of a ternary Half-Heusler alloy, YAuPb, using the tight-binding approach. We have calculated some important topological properties which includes$-$ finding nodes and their chiralities, Berry curvature ($\boldsymbolΩ$) and the surface-states. Based on the study of these properties, we categorise the material as non-trivial topological semimetal. Besides the topological behaviours, we present a comparative study of temperature dependent transport properties corresponding to the chemical potential ($μ$) of the Fermi level and the node points. The results obtained from the calculations of electrical conductivity per unit relaxation time ($\boldsymbolσ/τ$) and the electronic part of thermal conductivity per unit relaxation time ($\boldsymbolκ_0$) indicates the conducting nature of the material to both the heat and electricity. Furthermore, the negative value of $S$ obtained, indicates the n-type behaviour of the compound. The calculated value of electronic specific heat (Pauli magnetic susceptibility) corresponding to Fermi level is $\sim 0.03 \hspace{1mm}(0.18) \times 10^{-2}$ $ Jmol^{-1}K^{-1}$ ($\sim 1.21 \hspace{1mm}(1.14) \times 10^{-10}$ $ m^{3}mol^{-1}$) at 50 (300) K. This work suggests that YAuPb is a promising candidate of non-trivial topological semimetals which can be employed in transmission of heat and electricity, and as n-type material within the temperature range of 50-300 K.

cond-mat.mtrl-sci↗

arXiv2020

Exploring the suitable theoretical approach for understanding the electronic and magnetic properties of $α$-Iron

We present a comparative electronic structure study using DFT and various beyond-DFT (DFT+$U$, $G_0W_0$, DFT+DMFT) methods for ferromagnetic Iron (Fe) to find better approach for describing the spectral properties of correlated magnetic system. The computed value of $U$ ($W$) is $\sim$5.4 ($\sim$0.8) eV. The calculated spectra of all methods are providing good agreement with experimental spectra (ES) for peaks' positions. But, the proper line shape is only found from DFT+DMFT with correct estimation of incoherent states, which depends on $J$ and form of local Coulomb interactions. The estimation of reduced magnetization as function of reduced temperature using DFT+DMFT shows good agreement with the experimental data. The insight of paramagnetic electronic structure of Fe is also explored. This work suggests that even for simple correlated magnetic metal, we need DFT+DMFT method to reproduce the ES with great accuracy.

cond-mat.str-el↗

arXiv2020

Coexistance of non-Fermi liquid behavior and bi-quadratic exchange coupling in La-substituted CeGe: Non-linear susceptibility and DFT + DMFT study

Studies connected with the investigations of non-Fermi liquid (NFL) systems continue to attract interest in condensed matter physics community. Understanding the anomalous physical properties exhibited by such systems and its related electronic structures is one of the central research topics in this area. In this context, Ce-based and Ce-site diluted (with non-magnetic ions) compounds provide a fertile playground. Here, we present a detailed study of non-linear DC susceptibility and combined density functional theory plus dynamical mean field theory (DFT+DMFT) on Ce0.24La0.76Ge. Theoretical investigation of 4f partial density of states, local susceptibility and self-energy demonstrates the presence of NFL behavior which is associated with fluctuating local moments. Non-linear DC susceptibility studies on this compound reveal that the transition from NFL state to the new phase is due to development of the bi-quadratic exchange coupling and it obeys the non-linear susceptibility scaling. Under the application of magnetic fields, local moments interact spatially through conduction electrons resulting in magnetic fluctuations. Our studies point to the fact that the origin of the observed bi-quadratic exchange coupling is due to the spatial magnetic fluctuations.

cond-mat.str-el↗

arXiv2020

Investigating the effect of temperature dependent many-body interactions on bulk electronic structures and the robust nature of (001) surface states of SnTe

Recently, SnTe has gained attention due to its non-trivial topological nature and eco-friendly thermoelectric applications. We report a detailed temperature dependent electronic structure and thermodynamic properties of this compound using DFT and GW methods. The calculated values of bandgaps by using PBEsol and $G_0W_0$ methods are found to be in good agreement with the experiment, whereas mBJ underestimates the bandgap. The estimated value of fully screened Coulomb interaction ($W$) for Sn (Te) 5$p$ orbitals is $\sim$1.39 ($\sim$1.70) eV. The nature of frequency dependent $W$ reveals that the correlation strength of this compound is relatively weaker and hence the excited electronic state can be properly studied by full-$GW$ many-body technique. The plasmon excitation is found to be important in understanding this frequency dependent $W$. In order to describe the experimental phonon modes, the long range Coulomb forces using nonanalytical term correction is considered. The temperature dependent electron-electron interactions (EEI) reduces the bandgaps with increasing temperature. The value of bandgap at 300 K is obtained to be $\sim$161 meV. The temperature dependent lifetimes of electronic state along W-L-$Γ$ direction are also estimated. This work suggests that EEI is important to explain the high temperature transport behaviour of SnTe. We have also explored the possibility of protecting the (001) surface states via mirror and time-reversal symmetry. These surface states are expected to be robust against the point and line defects.

cond-mat.str-el↗

arXiv2019

A detailed electronic structure study of Vanadium metal by using different beyond-DFT methods

We report a detailed electronic structure calculation for Vanadium (V) using DFT, DFT+$U$, $G_0W_0$, $GW_0$ and DFT+DMFT methods. The calculated values of $W$, $U$ and $J$ by cRPA method are $\sim$1.1, $\sim$3.4 and $\sim$0.52 eV, respectively. The comparison between calculated spectra (CS) and experimental spectra (ES) suggests that $W$ ($U$) is more accurate for DFT+$U$ (DFT+DMFT) method. The CS, obtained by these methods, give fairly good agreement with ES for peaks' positions except $GW_0$. The shallowness of the dips lying $\sim$ -1.5 eV and $\sim$1.0 eV in ES are properly explained by DFT+DMFT method only, due to the presence of incoherent $t_{2g}$ states. This work suggests that for the proper explanation of ES, sophisticated many-body theory is needed even for the simple metal.

cond-mat.str-el↗

arXiv2017

Studying the effect of different exchange correlation functionals on the structural and electronic properties of a half-Heusler NaAuS compound

Theoretically, NaAuS is predicted as topological insulator, while no detail electronic structure study has been done for this compound. Here, we report the structural and electronic properties of NaAuS by using LDA, PBEsol, PBE and revPBE exchange correlation functionals. The calculated values of equilibrium lattice constant for LDA, PBEsol, PBE and revPBE exchange correlation functionals are found to be $\sim$6.128 Å, $\sim$6.219 Å, $\sim$6.353 Å and $\sim$6.442 Å, respectively. The bulk modulus predicted by LDA, PBEsol, PBE and revPBE exchange correlation functionals is $\sim$66.6, $\sim$56.4, $\sim$46.5 and $\sim$39.3 GPa, respectively. Hence, the order of calculated values of bulk modulus is consistent with the order of calculated values of equilibrium lattice parameters for these exchange correlation functionals. The spread of total density of states below the Fermi level decreases as the exchange correlation functional changes from LDA to PBEsol to PBE to revPBE, which is also found to be consistent with the order of bulk modulus for these exchange correlation functionals. In presence of spin-orbit coupling, a direct band gap is observed in NaAuS compound, which is found to be $\sim$0.26, $\sim$0.25, $\sim$0.24 and $\sim$0.23 eV for LDA, PBEsol, PBE and revPBE exchange correlation functionals, respectively. Here, NaAuS is found to be topological insulator as it shows band inversion at $Γ$ point. The calculated values of band inversion strength for LDA (PBEsol) and PBE (revPBE) exchange correlation functionals are $\sim$1.58 eV ($\sim$1.57 eV) and $\sim$1.50 eV ($\sim$1.47 eV), respectively.

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