arXiv subjects

Poonam Kumari

Publications and source records attributed to Poonam Kumari.

7 recordsLinked to original sources

arXiv2026

An iterative method bridging DFT, disorder averaging, and experiment in intercalated materials: application to Au-intercalated graphene

Intercalation can strongly modify the electronic dispersion of a host material, as directly revealed by angle-resolved photoemission spectroscopy (ARPES). We develop a general iterative method combining density functional theory (DFT), tight-binding (TB), disorder averaging within the self-consistent T-matrix approximation (SCTMA), and experiment, to construct an effective model of the intercalated system. DFT identifies the relevant microscopic degrees of freedom and constrains selected model parameters, while comparison of SCTMA calculations with experiment guides their further refinement. We apply this method to graphene intercalated with Au clusters and show that it reproduces the main ARPES signatures of the Au-cluster phase, including the broadening of the V12an Hove singularity and the emergence of kink-like features in the dispersion. The essential microscopic ingredients identified by the analysis are the hybridization between selected intercalant orbitals and the graphene states, together with an intercalation-induced local scattering potential.

cond-mat.mes-hall↗

arXiv2026

Effects of gold cluster intercalation in graphene: stationary waves and modified QPI features

Gold intercalation beneath epitaxial graphene on SiC produces a cluster phase with unusual standing waves and quasiparticle-interference (QPI) features concentrated near the graphene M points. We show that this can be explained by Au intercalation below graphene hollow sites, which induces a local scattering potential on the six surrounding carbon atoms. Within a T-matrix treatment, this ring-like scatterer produces elliptical QPI structures centered near M, in agreement with the experimental FT-STS measurements. We further show that these QPI features naturally generate the nearly stationary standing-wave patterns observed in real space. Finally, we compute the local-density-of-states contrast on and off a small cluster and show that its sign and magnitude are strongly energy dependent, consistent with the experimental observations.

cond-mat.mes-hall↗

arXiv2025

Modelling spin-orbitronics effects at interfaces and chiral molecules

Using orbital angular momentum (OAM) currents in nanoelectronics, for example, for magnetization manipulation via spin-orbit torque (SOT), represents a growing field known as "spin-orbitronics". Here, using the density functional theory (DFT) and the real-time dynamics of electronic wave packets, we explore a possibility of generation and propagation of orbital currents in two representative systems: an oxidized Cu surface (where large OAMs are known to form at the Cu/O interface) and a model molecular junction made of two carbon chains connected by a chiral molecule. In the Cu/O system, the orbital polarization of an incident wave packet from the Cu lead is strongly enhanced at the Cu/O interface but then rapidly decays in the bulk Cu due to orbital quenching of asymptotic bulk states. Interestingly, if a finite transmission across the oxygen layer is allowed (in a tunnel junction geometry, for example), a significant spin-polarization of transmitted (or reflected) currents is instead predicted which persists at a much longer distance and can be further tuned by an applied in-plane voltage. For the molecular junction, the mixing of the carbon $p_x$ and $p_y$ (degenerate) channels by the chiral molecular orbital gives rise not only to an efficient generation of orbital current but also to its long-range propagation along the carbon chain.

cond-mat.mtrl-sci↗

arXiv2022

Vertical Heterostructures between Transition-Metal Dichalcogenides -- A Theoretical Analysis of the NbS$_2$/WSe$_2$ junction

Low-dimensional metal-semiconductor vertical heterostructures (VH) are promising candidates in the search of electronic devices at the extreme limits of miniaturization. Within this line of research, here we present a theoretical/computational study of the NbS$_2$/WSe$_2$ metal-semiconductor vertical hetero-junction using density functional theory (DFT) and conductance simulations. We first construct atomistic models of the NbS$_2$/WSe$_2$ VH considering all the five possible stacking orientations at the interface, and we conduct DFT and quantum-mechanical (QM) scattering simulations to obtain information on band structure and transmission coefficients. We then carry out an analysis of the QM results in terms of electrostatic potential, fragment decomposition, and band alignment. The behavior of transmission expected from this analysis is in excellent agreement with, and thus fully rationalizes, the DFT results, and the peculiar double-peak profile of transmission. Finally, we use maximally localized Wannier functions, projected density of states (PDOS), and a simple analytic formula to predict and explain quantitatively the differences in transport in the case of epitaxial misorientation. Within the class of Transition-Metal Dichalcogenide systems, the NbS$_2$/WSe$_2$ vertical heterostructure exhibits a wide interval of finite transmission and a double-peak profile, features that could be exploited in applications.

cond-mat.mtrl-sci↗

arXiv2022

Microscopic Origin Of Room Temperature Ferromagnetism in a Double Perovskite Sr$_2$FeReO$_6$: a first principle and model Hamiltonian study

The puzzling observation of room temperature ferromagnetism in double perovskites (A$_2$BB$'$O$_6$), despite having the magnetic lattice of B-ions diluted by non-magnetic B$'$-ions, have been examined for Sr$_2$FeReO$_6$. {\it Ab-initio} spin spiral electronic structure calculations along various high symmetry directions in reciprocal space are used to determine the exchange interactions entering an extended Heisenberg model, which is then solved classically using Monte Carlo simulations to determine the ferromagnetic transition temperature T$_c$. We find that one must consider onsite Coulomb interactions at the nonmagnetic Re sites ($U$) in order to obtain a T$_c$ close to the experimental value. Analysis of the $ab$-$initio$ electronic structure as well as an appropriate model Hamiltonian trace the origin of enhancement in T$_c$ with $U$ to the enhanced exchange splitting that is introduced at these sites. This in turn destabilizes the antiferromagnetic exchange channels, thereby enhancing the T$_c$. The role of occupancy at the non-magnetic sites is examined by contrasting with the case of Sr$_2$FeMoO$_6$.

cond-mat.str-el↗

arXiv2017

Structural distortions in monolayers of binary semiconductors

We examine the structural properties of free standing II-VI and III-V semiconductors at the monolayer limit within first principle density functional theory calculations. A non-polar buckled structure was found to be favoured over a polar buckled structure. While an obvious reason for this may be traced to the contribution from dipole dipole interactions present in the polar structure which would destabilize it with respect to the nonpolar structure, Coulomb interactions between electrons on the cations and anions are found to be the reason for the nonpolar structure to be favoured. A route to tune the Coulomb interaction between the electrons on the cations and anions is through biaxial tensile strain. This allows for a planar graphitic phase in CdS to be stabilized at just 2\% tensile strain. Strain also shifts the valence band maximum from the $Γ$ point to the K point opening up opportunities for exploring spin-valley physics in these materials.

cond-mat.mes-hall↗

arXiv2016

Communicating Data Quality in On-Demand Curation

On-demand curation (ODC) tools like Paygo, KATARA, and Mimir allow users to defer expensive curation effort until it is necessary. In contrast to classical databases that do not respond to queries over potentially erroneous data, ODC systems instead answer with guesses or approximations. The quality and scope of these guesses may vary and it is critical that an ODC system be able to communicate this information to an end-user. The central contribution of this paper is a preliminary user study evaluating the cognitive burden and expressiveness of four representations of "attribute-level" uncertainty. The study shows (1) insignificant differences in time taken for users to interpret the four types of uncertainty tested, and (2) that different presentations of uncertainty change the way people interpret and react to data. Ultimately, we show that a set of UI design guidelines and best practices for conveying uncertainty will be necessary for ODC tools to be effective. This paper represents the first step towards establishing such guidelines.

cs.DB↗