arXiv subjects

Subhadeep Bandyopadhyay

Publications and source records attributed to Subhadeep Bandyopadhyay.

14 recordsLinked to original sources

arXiv2026

Design of altermagnetism in oxide superlattices exploiting interface effects and quantum confinement

The discovery of altermagnetism has initiated intensive research and opened new avenues for spin- tronic and transport applications. While current efforts are mostly focused on bulk materials which are typically insulating, here we propose design strategies to achieve a combination of altermag- netism and metallicity in oxide superlattices by exploiting symmetry breaking, electrostatic doping and confinement. While bulk SrCrO3 does not exhibit altermagnetism due to compensating effects between adjacent layers our density functional theory calculations with a Hubbard U parameter re- veal, that a single SrCrO3 layer confined in a (SrCrO3)1/(SrTiO3)1(001) superlattice (SL) exhibits a sizable non-relativistic spin splitting (NRSS) up to 350 meV with bulk d-wave nature due to the coexistence of orbital ordering and octahedral rotations (OORs). Since this system is insulating, we extend to SrCrO3/LaCrO3(001) SLs. In the (SrCrO3)4/(LaCrO3)4(001) SL the combination of a polar discontinuity at the interface and stronger OORs promotes metallic d-wave altermagnetism. The NRSS of up to 120 meV is contributed by the interfacial Cr d bands at the Fermi level with indications for a spin-selective Fermi surface nesting. These findings establish oxide superlattices as a promising platform to realize and explore altermagnetism for quantum transport and spintronic functionalities

cond-mat.mtrl-sci↗

arXiv2026

Why is the $d$-Wave spin splitting in CuF$_2$ bulk-like?

With the advent of nonrelativistic spin splitting in collinear compensated antiferromagnets, several candidate materials have also been proposed, among which the family of transition-metal difluorides stands out as a prominent example. Within this family, most members exhibit planar $d$-wave spin splitting, whereas CuF$_2$ shows bulk $d$-wave splitting with an explicit $k_z$ dependence. In this work, we show that this transition from planar to bulk $d$-wave splitting in CuF$_2$ is primarily driven by the antipolar displacements of the F ions, which are absent in the tetragonal rutile structure of the other family members. Our calculations reveal that these additional structural distortions introduce an extra plane of anisotropic magnetization density, giving rise to an additional totally symmetric component of the magnetic octupole tensor. The $k$-space representation of this octupole component, consequently, dictates an additional direction of spin splitting, thereby transforming the $d$-wave spin splitting pattern from planar to bulk-like. We further analyze the effect of spin-orbit coupling on the magnetic octupoles and the resulting spin splitting in the band structure. Our work highlights the possibility of controlling the pattern of nonrelativistic spin splitting through structural modifications, for example, via the application of external pressure.

cond-mat.mtrl-sci↗

arXiv2025

A Universal Framework for Controlling Non-Relativistic Spin Splitting

Non-relativistic spin splitting in antiferromagnets has recently attracted considerable attention. Here we present a universal framework for controlling such spin splitting by identifying and manipulating the key atomic distortions that govern it through external perturbations. We demonstrate this concept by tuning the spin-splitting energy in three representative materials with diverse symmetries, inversion-symmetric MnF$_2$, ferroelectric BaCuF$_4$, and LaMnO$_3$/RMnO$_3$ superlattices. Our results emphasize the essential role of higher-order magnetic multipoles and the intrinsic structure-spin correlations in these systems, thereby advancing current efforts to control spin splitting in real materials and motivating future experimental studies.

cond-mat.mtrl-sci↗

arXiv2025

Rational Control of Magnonic and Electronic Band Splittings

We provide a theoretical demonstration of controllable non-relativistic spin splitting in both electronic and magnonic bands via targeted structural distortions tied to specific phonon modes. Using MnF$_2$ as a model system, we identify a $d$-wave magnon band splitting between magnon modes of specific handedness, directly correlated with the non-relativistic spin splitting observed in the electronic structure. Crucially, we show that structural distortions associated with the A$_{2u}$ and A$_{1g}$ phonon modes (8.52 and 9.74 THz) modulate these splittings without altering the antiferromagnetic order. The effect originates from changes in the nonmagnetic ligand environment, highlighting the key role of lattice degrees of freedom in governing spin dynamics. Our findings establish a novel route for structure-mediated control of spin splitting, opening possibilities for tunable magnonic and spintronic functionalities in antiferromagnetic materials.

cond-mat.mtrl-sci↗

arXiv2025

Bulk photovoltaic effect in ferroelectric and antiferroelectric phases of antimony sulphoiodide investigated by means of ab-initio simulations

We employ first-principles calculations to investigate the ferroelectric properties and the bulk photovoltaic effect (BPVE) of antimony sulfur iodide (SbSI). The BPVE enables direct sunlight-to-electricity conversion in homogeneous materials and, in ferroelectric compounds, can be tuned via an electric field controlling the polarization. However, most ferroelectrics are oxides with large band gaps exceeding the energy of visible light, thereby limiting their photovoltaic performance. SbSI, featuring a visible-range band gap, combines remarkable photovoltaic capabilities with a spin-textured band structure, coupling charge and spin degrees of freedom. Our calculations predict ferroelectric and antiferroelectric phases with comparable band gaps but distinct spin textures, relevant for spintronics applications. The BPVE is driven by the linear and circular photogalvanic effects, exhibiting high photoconductivities under visible light. Furthermore, it serves as a diagnostic tool to identify the material phase, with the circular photogalvanic effect reflecting spin texture changes. Thanks to its multifunctional properties, SbSI emerges as a promising candidate for solar energy conversion and advanced electronics, with potential applications extending to spintronics.

cond-mat.mtrl-sci↗

arXiv2025

Structurally triggered orbital and charge orderings in TlMnO$_3$ and related compounds

Rare earth perovskites ($R^{3+}$M$^{3+}$O$_3$), with $e_g^1$ electronic occupation of the M $d$ states, display different types of metal-insulator transition. For manganites (M=Mn), metal-insulator transition is usually induced by the Jahn-Teller ($JT$) distortions, which stabilize orbital orderings (OO) at Mn sites. Among them, LaMnO$_3$ shows a $C$ type OO and crystallizes with $Pbnm$ structure. Whereas, TlMnO$_3$ shows a very distinct $G$ type OO with an unusual $P\overline{1}$ structure. Employing first principles calculations, and symmetry mode analysis we rationalize structural and electronic origin of $G$-type OO in TlMnO$_3$. Going further, we consider nickelates (M=Ni), where metal-insulator transition is driven by a breathing distortion, which stabilizes the charge ordering (CO) at Ni sites. Interestingly, different $JT$ and breathing distortions are very similar MO$_6$ octahedral distortions and stem from high frequency phonon modes of ideal $Pm\overline3m$ structure. Our comparative study reveals that following a common triggering mechanism these modes appear in their respective ground states.

cond-mat.str-el↗

arXiv2025

Designing Non-Relativistic Spin Splitting in Oxide Perovskites

We investigate the role of atomic distortions in non-relativistic spin splitting in perovskite oxides with Pbnm symmetry. Using LaMnO3 as a representative material, we analyze its non-relativistic spin splitting through a combined phonon and multipolar analysis. Our study provides key insights into how structural distortions and magnetic ordering drive ferroically ordered magnetic multipoles, which, in turn, give rise to non-relativistic spin splitting. Based on these findings, we propose three strategies for engineering non-relativistic spin splitting: modifying the A-site cation size, strain engineering, and electric field control in superlattice structures. Our work establishes a framework for designing non-relativistic spin splitting in the Brillouin zone of oxide perovskites.

cond-mat.mtrl-sci↗

arXiv2024

In-plane magnetization orientation driven topological phase transition in OsCl$_3$ monolayer

The quantum anomalous Hall effect resulting from the in-plane magnetization in the OsCl$_3$ monolayer is shown to exhibit different electronic topological phases determined by the crystal symmetries and magnetism. In this Chern insulator, the Os-atoms form a two dimensional planar honeycomb structure with an easy-plane ferromagnetic configuration and the required non-adiabatic paths to tune the topology of electronic structure exist for specific magnetic orientations based on mirror symmetries of the system. Using density functional theory (DFT) calculations, these tunable phases are identified by changing the orientation of the magnetic moments. We argue that in contrast to the buckled system, here the Cl-ligands bring non-trivial topology into the system by breaking the in-plane mirror symmetry. The interplay between the magnetic anisotropy and electronic band-topology changes the Chern number and hence the topological phases. Our DFT study is corroborated with comprehensive analysis of relevant symmetries as well as a detailed explanation of topological phase transitions using a generic tight binding model.

cond-mat.str-el↗

arXiv2023

Latent electronic (anti-)ferroelectricity in BiNiO$_3$

BiNiO$_3$ exhibits an unusual metal-insulator transition from $Pnma$ to $P\overline{1}$ that is related to charge ordering at the Bi sites, which is intriguingly distinct from the charge ordering at Ni sites usually observed in related rare-earth nickelates. Here, using first principles calculations, we first rationalize the phase transition from $Pnma$ to $P\overline{1}$, revealing an overlooked intermediate $P2_1/m$ phase and a very unusual phase transition mechanism. Going further, we point out that the charge ordering at Bi sites in the $P\overline{1}$ phase is not unique. We highlight an alternative polar orderings giving rise to a ferroelectric $Pmn2_1$ phase nearly degenerated in energy with $P\overline{1}$ and showing an in-plane electric polarisation of 53 $μC $/cm$^2$ directly resulting from the charge ordering. The close energy of $Pmn2_1$ and $P\overline{1}$ phases, together with low energy barrier between them, make BiNiO$_3$ a potential electronic antiferroelectric in which the field-induced transition from non-polar to polar would relate to non-adiabatic inter-site electron transfer. We also demonstrate the possibility to stabilize an electronic ferroelectric ground state from strain engineering in thin films, using an appropriate substrate

cond-mat.str-el↗

arXiv2023

Effect of Spin Orbit Coupling in non-centrosymmetric half-Heusler alloys

Spin-orbit coupled electronic structure of two representative non-polar half-Heusler alloys, namely 18 electron compound CoZrBi and 8 electron compound SiLiIn have been studied in details. An excursion through the Brillouin zone of these alloys from one high symmetry point to the other revealed rich local symmetry of the associated wave vectors resulting in non-trivial spin splitting of the bands and consequent diverse spin textures in the presence of spin-orbit coupling. Our first principles calculations supplemented with low energy $\boldsymbol{k.p}$ model Hamiltonian revealed the presence of linear Dresselhaus effect at the X point having $D_{2d}$ symmetry and Rashba effect with both linear and non-linear terms at the L point with $C_{3v}$ point group symmetry. Interestingly we have also identified non-trivial Zeeman spin splitting at the non-time reversal invariant W point and a pair of non-degenerate bands along the path $Γ$ to L displaying vanishing spin polarization due to the non-pseudo polar point group symmetry of the wave vectors. Further a comparative study of CoZrBi and SiLiIn suggest, in addition, to the local symmetry of the wave vectors, important role of the participating orbitals in deciding the nature and strength of spin splitting. Our calculations identify half-Heusler compounds with heavy elements displaying diverse spin textures may be ideal candidate for spin valleytronics where spin textures can be controlled by accessing different valleys around the high symmetry k-points.

cond-mat.mtrl-sci↗

arXiv2022

Exchange interactions and spin dynamics in the layered honeycomb ferromagnet CrI$_3$

We derive the microscopic spin Hamiltonian for rhombohedral CrI$_3$ using extensive first-principles density functional theory (DFT) calculations which incorporate spin-orbit coupling and Hubbard U. Our calculations indicate a dominant nearest-neighbor ferromagnetic Heisenberg exchange with weaker further-neighbor Heisenberg terms. In addition, we find a Dzyaloshinskii-Moriya interaction which primarily drives a topological gap in the spin-wave spectrum at the Dirac point, and uncover a non-negligible antiferromagnetic Kitaev coupling between the S=3/2 Cr moments. The out-of-plane magnetic moment is stabilized by weak symmetric bond-dependent terms and a local single-ion anisotropy. Using linear spin wave theory, we find that our exchange parameters are in reasonably good agreement with inelastic neutron scattering (INS) experiments. Employing classical Monte Carlo simulations, we study the magnetic phase transition temperature $T_c$ and its evolution with an applied in-plane magnetic field. We further demonstrate how future high-resolution INS experiments on the magnon dispersion of single crystals in an in-plane magnetic field may be used to quantitatively extract the strength of the antiferromagnetic Kitaev exchange coupling.

cond-mat.str-el↗

arXiv2020

Superconductivity in Infinite-layer Nickelates : Role of Non-zero f-ness

Employing first-principles density functional theory calculations and Wannierization of the low energy band structure, we analyze the electronic structure of undoped, infinite-layer nickelate compounds, NdNiO$_2$, PrNiO$_2$ and LaNiO$_2$. Our study reveals important role of non-zero $f$-ness of Nd and Pr atoms, as opposed to $f^{0}$ occupancy of La. The non-zero $f$-ness becomes effective in lowering the energy of the rare-earth 5$d$ hybridized axial orbital, thereby enhancing the electron pockets and influencing the Fermi surface topology. The Fermi surface topology of NdNiO$_2$ and PrNiO$_2$ is strikingly similar, while differences are observed for LaNiO$_2$. This difference shows up in computed doping dependent superconducting properties of the three compounds within a weak coupling theory. We find two gap superconductivity for NdNiO$_2$ and PrNiO$_2$, and possibility of a single gap superconductivity for LaNiO$_2$ with the strength of superconductivity suppressed by almost a factor of two, compared to Nd or Pr compound.

cond-mat.supr-con↗

arXiv2020

Orbital Selective Superconductivity in a Two-band Model of Infinite-Layer Nickelates

In the present study, we explore superconductivity in NdNiO$_2$ and LaNiO$_2$ employing a first-principles derived low-energy model Hamiltonian, consisting of two orbitals: Ni $x^{2}$-$y^{2}$, and an {\it axial} orbital. The {\it axial} orbital is constructed out of Nd/La $d$, Ni 3$z^{2}$-$r^{2}$ and Ni $s$ characters. Calculation of the superconducting pairing symmetry and pairing eigenvalue of the spin-fluctuation mediated pairing interaction underlines the crucial role of inter-orbital Hubbard interaction in superconductivity, which turns out to be orbital-selective. The axial orbital brings in materials dependence in the problem, making NdNiO$_2$ different from LaNiO$_2$, thereby controlling the inter-orbital Hubbard interaction assisted superconductivity.

cond-mat.supr-con↗

arXiv2017

Disorder induced lifetime effects in binary disordered systems : a first principles formalism and an application to doped Graphene

In this work the conducting properties of graphene lattice with a particular concentration of defect (5\% and 10\%) has been studied. The real space block recursion method introduced by Haydock et al. has been used in presence of the random distribution of defects in graphene. This Green function based method is found more powerful than the usual reciprocal based methods which need artificial periodicity. Different resonant states appear because of the presence of topological and local defects are studied within the framework of Green function.

cond-mat.mtrl-sci↗