arXiv subjects

Shivalika Sharma

Publications and source records attributed to Shivalika Sharma.

7 recordsLinked to original sources

arXiv2026

A first-principles study of bcc chromium beyond the generalized gradient approximation (GGA)

The study of magnetism in transition metals is a cornerstone in understanding complex electronic and magnetic interactions in condensed matter systems. Among transition metal elements, body-centered cubic (bcc) chromium stands out because of its spin-density wave (SDW) ground state, posing a long-standing challenge for density functional theory (DFT). Conventional functionals, such as the generalized-gradient approximation (GGA) and the local-density approximation (LDA), fail to predict this experimentally observed incommensurate SDW as the ground state. In this study, we present a comprehensive DFT analysis of bcc Cr employing GGA and a variety of meta-GGA functionals. We evaluated total energies, structural parameters, and magnetic properties across a wide range of SDW wave vectors. Our results show that all meta-GGA functionals overestimate the local magnetic moments and enhance the nodal magnetic frustration, destabilizing the SDW state relative to the commensurate antiferromagnetic (AF) configuration. Tao-Perdew-Staroverov-Scuseria (TPSS) yields results closest to those of the GGA, thus providing the most adequate description of bcc Cr among the meta-GGA functionals. These results emphasize the need for the further development of non-local or hybrid functionals tailored for complex magnetic systems.

cond-mat.mtrl-sci↗

arXiv2026

Strain-induced structural transitions in (111)-oriented (LaMnO$_3$)$_{2n}|$(SrMnO$_3$)$_n$ superlattices

By means of first-principles electronic structure calculations, we hereby investigate the structural transitions induced by epitaxial strain in (111)-oriented (LaMnO$_3$)$_{2n}|$(SrMnO$_3$)$_n$ superlattices, with $n=2,4,6$. All superlattices in the explored range of strain are shown to prefer a half-metallic ferromagnetic order where the local magnetic moments are coupled to volume-breathing distortions. More in detail, our results reveal that thickness plays a crucial role in the response to epitaxial strain, which is particularly evident in the resulting tilt pattern of the oxygen octahedra. The thinnest superlattice, for $n=2$, always adopts the $a^-a^-a^-$ tilt pattern and the competing $a^-a^-c^+$ tilt pattern can be stabilized as a metastable state only in presence of compressive strain. Instead, the superlattice with $n=4$ favours the $a^-a^-c^+$ tilt pattern at equilibrium conditions, but the in-phase rotations around the third pseudocubic axis are so fragile that the $a^-a^-a^-$ pattern is recovered under a tiny amount of either compressive or tensile strain. The superlattice with $n=6$ exhibits a more nuanced behaviour: compressive strain drives a transition from $a^-a^-c^+$ to $a^-a^-a^-$, whereas tensile strain preserves the $a^-a^-c^+$ tilt pattern and significantly accentuates the structural differences between the two inequivalent sublattices within this symmetry. In fact, the Jahn-Teller distortions are quenched in one of the sublattices, leading to enhanced volume-breathing distortions and corresponding enhanced charge and spin oscillations. This suggests that Hund's physics may be more relevant in this regime of tensile strain, maximizing the interplay between strong electronic correlations and structural effects.

cond-mat.mtrl-sci↗

arXiv2026

Exchange interactions and finite-temperature magnetism in (111)-oriented (LaMnO$_3$)$_{2n}$|(SrMnO$_3$)$_n$ superlattices

We present a first-principles investigation of magnetic exchange interactions and critical behavior in (111)-oriented (LaMnO$_3$)$_{2n}$|(SrMnO$_3$)$_n$ superlattices for $n=2,4,6$. For all superlattices under investigation, we find robust half-metallic ferromagnetism extending across all the layers of both component regions. Changing octahedral tilt patterns is found to have negligible effects on the magnetic properties, despite determining the presence or absence of small Jahn-Teller distortions. The analysis of the response of the magnetic coupling to a variation of the Coulomb interaction parameters demonstrates that ferromagnetism is driven by a double-exchange mechanism involving itinerant $e_g$ electrons, while its final strength is hampered by antiferromagnetic contributions due to the superexchange of localized $t_{2g}$ electrons. Multi-scale simulations based on atomistic spin dynamics show that the thinnest superlattices, $n=2,4$, possess an ordering temperature that is at least comparable to that of La$_{2/3}$Sr$_{1/3}$MnO$_3$. Conversely, as thickness increases, a two-phase behavior emerges, where the SrMnO$_3$ region loses long-range order faster than the LaMnO$_3$ region. While the global ordering temperature increases together with thickness, we argue that the high-temperature regime for the observed two-phase behavior is not representative of the real physical system, which will undergo a combined electronic, magnetic and structural phase transition as soon as the long-range order is lost inside the SrMnO$_3$ region. This study provides insights into the emergent magnetic phases and transition temperatures relevant to oxide heterostructures.

cond-mat.str-el↗

arXiv2025

Exploring strong electronic correlations in the breathing kagome metal Fe$_3$Sn

Kagome metals have emerged as pivotal materials in condensed matter physics due to their unique geometric arrangement and intriguing electronic properties. Understanding the origin of magnetism in these materials, particularly in iron rich Fe-Sn binary compounds like Fe$_3$Sn, holds a significant importance, as they represent potential candidates for permanent magnets with a high Curie temperature and a strong magnetic anisotropy. In the present study, we employ density-functional theory and dynamical mean-field theory to analyze the electronic structure and magnetic properties of Fe$_3$Sn. Our investigation reveals the presence of several nearly-flat bands and Weyl nodes at low excitation energies. The inclusion of local correlation effects is shown to push these features even closer to the Fermi energy, which may be important for their manipulation via external stimuli. Regarding magnetism, the Hubbard-like interaction leads to an increase of orbital polarization at the expenses of a minor reduction of the spin moment. The magnetic anisotropy energy exhibits a strong dependence on the particular choice of the Coulomb interaction parameters. Additionally, our detailed analysis of the interatomic exchange interactions indicates a significant contribution from the antisymmetric exchange, i.e. the Dzyaloshinskii-Moriya interaction, which showcases the existence of magnetic chirality in the system. Overall, our investigation highlights a strong interplay between the flat bands near the Fermi level, the local Coulomb interaction and the triangular geometry of the lattice, which plays a crucial role in driving the magnetic properties of this material.

cond-mat.str-el↗

arXiv2024

Revisiting magnetic exchange interactions in transition metal doped Bi$_2$Se$_3$ using DFT+MFT

Topological insulators doped with magnetic impurities has become a promising candidate for Quantum Anomalous Hall Effect (QAHE) in the dilute doping limit. The crucial factor in realizing the QAHE in these systems is the spontaneous Ferromagnetic (FM) ordering between the doped magnetic atoms. Hence, understanding the magnetic exchange interaction between the magnetic atoms becomes essential. In this work, we use the Density functional theory (DFT) and Magnetic force theorem (MFT) to calculate the magnetic exchange interaction between magnetic impurities (V, Cr, Mn, Fe) in the host Bi2Se3. Through an orbital decomposition of the calculated exchange, we can identify the nature and origin of the exchange mechanism that depends on the type of magnetic atoms, doping concentration, host material etc. Our results show that Cr doping results in an insulating state, a prerequisite for the QAHE, that remains robust against doping concentration and local correlation. In this case, the short-ranged superexchange and long-ranged exchange via the p-orbitals of the host results in an FM order. For other doped systems (V, Mn and Fe doped), their electronic configuration and local octahedral environment open the possibility of finite carrier density at the Fermi energy. Depending on the type of this carrier (electron/hole) and their localized/delocalized nature, a short-ranged double exchange / long-ranged RKKY mechanism could occur between the magnetic atoms.

cond-mat.mtrl-sci↗

arXiv2023

Magnetism in AV3Sb5 (A = Cs, Rb, K): Complex Landscape of the Dynamical Magnetic Textures

We have investigated the dynamical magnetic properties of the V-based kagome stibnite compounds by combining the ab-initio calculated magnetic parameters of a spin Hamiltonian like inter-site exchange parameters, magnetocrystalline anisotropy and site projected magnetic moments, with full-fledged simulations of atomistic spin-dynamics. Our calculations reveal that in addition to a ferromagnetic order along the [001] direction, the system hosts a complex landscape of magnetic configurations comprised of commensurate and incommensurate spin-spirals along the [010] direction. The presence of such chiral magnetic textures may be the key to solve the mystery about the origin of the experimentally observed inherent breaking of the C6 rotational symmetry- and the time-reversal symmetry.

cond-mat.mtrl-sci↗

arXiv2023

Magnetism in AV3Sb5 (Cs, Rb, K): Origin and Consequences for the Strongly Correlated Phases

The V-based kagome systems AV3Sb5 (A = Cs, Rb and K) are unique by virtue of the intricate interplay of non-trivial electronic structure, topology and intriguing fermiology, rendering them to be a playground of many mutually dependent exotic phases like charge-order and superconductivity. Despite numerous recent studies, the interconnection of magnetism and other complex collective phenomena in these systems has yet not arrived at any conclusion. Using first-principles tools, we demonstrate that their electronic structures, complex fermiologies and phonon dispersions are strongly influenced by the interplay of dynamic electron correlations, non-trivial spin-polarization and spin-orbit coupling. An investigation of the first-principles-derived inter-site magnetic exchanges with the complementary analysis of q-dependence of the electronic response functions and the electron-phonon coupling indicate that the system conforms as a frustrated spin-cluster, where the occurrence of the charge-order phase is intimately related to the mechanism of electron-phonon coupling, rather than the Fermi-surface nesting.

cond-mat.str-el↗