arXiv subjects

Suvadip Das

Publications and source records attributed to Suvadip Das.

8 recordsLinked to original sources

arXiv2026

Study of the Anomalous Hall effect by tuning the spin orientation in the Altermagnetic material CrSb

Recent development in the field of altermagnetism, and increased demand for the search of applications of anomalous hall effect have ushered in a new era for novel quantum phases in materials. Quantum materials previously anticipated to be scientifically predictable have unfolded novel properties that brought them into the spotlight. These manifestations have led us to rethink our understanding of existing classification of magnetic materials and preexisting notions about anomalous hall effect in the light of topologically nontrivial phases of matter. One such recent de- velopment lies in the novel class of alter-magnetic materials with prospect for quantum computing. In this article, we delineate the spin and orbital resolved electronic spectrum, mode-decomposed phonon dispersion relations, geometrical berry curvature and topological surface states and their implications on anomalous Hall conductivity in the promising altermagnetic compound CrSb. We further utilize first principles calculations coupled with computationally efficient maximally localized wannier states of numerous magnetic configurations of the altermagnet to simulate the effect of external fields and elucidate the fact that the linear behaviour of anomalous hall conductivity with magnetization does not necessarily hold true for all magnetic classes, such as altermagnets.

cond-mat.str-el↗

arXiv2026

Unraveling the significance of Raman modes, Gruneisen parameters and phonon lifetimes in the hexagonal allotropes of Silicon and Germanium compounds

Advancement in quantum information and quantum technologies has ushered in a new era of technological revolution in large scale atomistic simulation and efficient system on a chip device fabrication. This has led to innovative ways of harnessing rigorous search algorithms for functional quantum materials and steered scientists to dig deeper into the world of quantum phenomenon and applications. In this work, we delineate the advanced electronic structure and vibrational properties utilizing the popular meta-GGA functionals, spectral signatures of the Raman active phonon modes, explored their average mean free paths, and whether they conserve helicity, by leveraging first principles density functional theory and density functional perturbation theory. A systematic analysis of the role of phonon lifetimes, consequences of phonon-phonon and three phonon scattering rates and phonon linewidths have been presented. Further, a study of the the frequency and temperature dependent Gruneisen parameter has been employed in conjecture with the temperature dependent thermal expansion and thermal conductivity to portray the effect of anharmonicity in the phonon spectra of these two materials. Finally, we provide strategies for tuning the properties of these materials in an effort to improve their efficacy for advanced thermoelectric, photovoltaic and optoelectronic device applications.

cond-mat.mtrl-sci↗

arXiv2025

The alloying of first-principles calculations with quasiparticle methodologies for the converged solution of the quantum many-electron states in the correlated compound Iron monoxide

Transition metal oxides belong to a genre of quantum materials essential for the exploration of theoretical methods for quantifying electronic correlation. Finding an efficient and accurate first principles method for the assertion of such physical properties is momentous for the predictive modelling of physics based thermoelectric and photovoltaic devices. Prior investigations have suggested that incorporation of the so called random phase approximation for the electronic screening interaction by adding up the electron hole pairs leads to significant improvement in the accuracy of first principle calculations. Nonetheless the method has seldom been adapted systematically for studying the properties of prototypical transition metal oxides, particularly that of the correlated compound Iron monoxide. In this work, we provide a benchmarking study of a variety of first principles methods such as the density functional theory artificially stabilized by Coulomb interactions, Hybrid functionals as well as the quasiparticle Greens function approach to self-energy interactions. A rigorous convergence of the self-consistent Dysons equations have been provided addressing the importance of initial choice of wavefunctions guided by first principles on the converged solutions and the interplay of various orbital degrees of freedom adjacent to the Fermi level. It is momentous to obtain accurate wavefunctions and many-electronic energy states for the quantification of correlation and efficient modelling of oxide interfaces for quantum applications. The study establishes the hybrid functional scheme as the optimal approach for the ideal trade-off between accuracy of the ground state wavefunctions and computational efficiency for large-scale simulations towards the efficient convergence of correlated electronic wavefunctions and low energy electronic properties.

cond-mat.mtrl-sci↗

arXiv2024

Origin of spin reorientation and intrinsic anomalous Hall effect in the kagome ferrimagnet TbMn6Sn6

TbMn$_6$Sn$_6$ has attracted a lot of recent interest for a variety of reasons, most importantly, because of the hypothesis that it may support quantum-limit Chern topological magnetism, derived from the kagome geometry. Besides, TbMn$_6$Sn$_6$ features a highly unusual magnetic reorientation transition about 100 K below the Curie point, whereby all spins in the system, remaining collinear, rotate by 90$^\circ$. In this work, we address both issues combining experiment, mean-field theory and first-principle calculations. Both magnetic reorientation and the unusual temperature dependence of the anomalous Hall conductivity (AHC) find quantitative explanation in the fact that Mn and Tb, by virtue of the Mermin-Wagner theorem, have very different spin dynamics, with Tb spins experiencing much more rapid fluctuation. We were able to cleanly extract the intrinsic AHC from our experiment, and calculated the same microscopically, with good semiquantitative agreement. We have identified the points in the band structure responsible for the AHC and showed that they are not the kagome-derived Dirac points at the K-corner of the Brillouin zone, as conjectured previously.

cond-mat.str-el↗

arXiv2024

Direct observation of altermagnetic band splitting in CrSb thin films

Altermagnetism represents an emergent collinear magnetic phase with compensated order and an unconventional alternating even-parity wave spin order in the non-relativistic band structure. We investigate directly this unconventional band splitting near the Fermi energy through spinintegrated soft X-ray angular resolved photoemission spectroscopy. The experimentally obtained angle-dependent photoemission intensity, acquired from epitaxial thin films of the predicted altermagnet CrSb, demonstrates robust agreement with the corresponding band structure calculations. In particular, we observe the distinctive splitting of an electronic band on a low-symmetry path in the Brilliouin zone that connects two points featuring symmetry-induced degeneracy. The measured large magnitude of the spin splitting of approximately 0.6 eV and the position of the band just below the Fermi energy underscores the signifcance of altermagnets for spintronics based on robust broken time reversal symmetry responses arising from exchange energy scales, akin to ferromagnets, while remaining insensitive to external magnetic fields and possessing THz dynamics, akin to antiferromagnets.

cond-mat.mtrl-sci↗

arXiv2021

Renormalized q-dependent Spin Susceptibility by inverting the Random Phase Approximation: Implications for quantitative assessment of the role of spin fluctuations in 2D Ising superconductor NbSe$_{2}$

Accurate determination of the full momentum-dependent spin susceptibility $χ(\mathbf{q}) $ is very important for the description of magnetism and superconductivity. While in principle the formalism for calculating $χ(\mathbf{q})$ in the linear response density functional theory (DFT) is well established, hardly any publicly available code includes this capability. Here, we describe an alternative way to calculate the static $χ(\mathbf{q})$, which can be applied to most common DFT codes without additional programming. The method combined standard fixed-spin-moment calculations of $χ(\mathbf{0}) $ with direct calculations of the energy of spin spirals stabilized by an artificial Hubbard interaction. From these calculations, $χ_{DFT}(\mathbf{q} )$ can be extracted by inverting the RPA formula. We apply this recipe to the recently discovered Ising superconductivity in NbSe$_2$ monolayer, one of the most exciting findings in superconductivity in recent years. It was proposed that spin fluctuations may strongly affect the parity of the order parameter. Previous estimates suggested proximity to ferromagnetism, $i.e.$, $χ(\mathbf{q})$ peaked at $\mathbf{q}=0$. We find that the structure of spin fluctuations is more complicated, with the fluctuation spectrum sharply peaked at $\mathbf{q}\approx (0.2,0)$. Such a spectrum would change the interband pairing interaction and considerably affect the superconducting state.

cond-mat.supr-con↗

arXiv2015

Non-stoichiometry and Defects in the Weyl Semimetals TaAs, TaP, NbP, and NbAs

We report a structural study of the Weyl semimetals TaAs, TaP, NbP, and NbAs, utilizing diffraction techniques (single crystal x-ray diffraction and energy dispersive spectroscopy) and imaging techniques (transmission electron microscopy/scanning transmission electron microscopy). We observe defects of various degrees, leading to non-stoichiometric single crystals of all four semimetals. While TaP displays a large pnictide deficiency with composition TaP$_{0.83(3)}$, and stacking faults accompanied by anti-site disorder and site vacancies, TaAs displays transition metal deficiency with composition Ta$_{0.92(2)}$As and a high density of stacking faults. NbP also displays pnictide deficiency, yielding composition NbP$_{0.95(2)}$, and lastly, NbAs display very little deviation from a 1:1 composition, NbAs$_{1.00(3)}$, and is therefore recommended to serve as the model compound for these semimetals.

cond-mat.mtrl-sci↗

arXiv2015

Convergence of quasiparticle self-consistent GW calculations of transition metal monoxides

Finding an accurate ab initio approach for calculating the electronic properties of transition metal oxides has been a problem for several decades. In this paper, we investigate the electronic structure of the transition metal monoxides MnO, CoO, and NiO in their undistorted rock-salt structure within a fully iterated quasiparticle self-consistent GW (QPscGW) scheme. We study the convergence of the QPscGW method, i.e., how the quasiparticle energy eigenvalues and wavefunctions converge as a function of the QPscGW iterations, and we compare the converged outputs obtained from different starting wavefunctions. We find that the convergence is slow and that a one-shot G$_0$W$_0$ calculation does not significantly improve the initial eigenvalues and states. It is important to notice that in some cases the "path" to convergence may go through energy band reordering which cannot be captured by the simple initial unperturbed Hamiltonian. When we reach a fully iterated solution, the converged density of states, band-gaps and magnetic moments of these oxides are found to be only weakly dependent on the choice of the starting wavefunctions and in reasonably good agreement with the experiment. Finally, this approach provides a clear picture of the interplay between the various orbitals near the Fermi level of these simple transition metal monoxides. The results of these accurate {\it ab initio} calculations can provide input for models aiming at describing the low energy physics in these materials.

cond-mat.str-el↗