arXiv subjects

Eklavya Thareja

Publications and source records attributed to Eklavya Thareja.

8 recordsLinked to original sources

arXiv2026

Stabilizing Magnetic Bubble Domains in Epitaxial 2D Magnet/Topological Insulator Heterostructures through Interfacial Interactions

Epitaxial heterostructures of two-dimensional van der Waals magnets and topological insulators offer a powerful platform for probing interfacial spin interactions that govern magnetic textures in low-dimensional quantum systems, while simultaneously enabling highly efficient, atomically thin spin-orbit-torque memory and computing architectures. Despite this promise, the fundamental role of these interfacial interactions in determining magnetic domain-phase stability remain largely uncharted. Here, we perform scanning transmission X-ray microscopy to image nanoscale magnetic textures in epitaxial Fe3GeTe2 Bi2Te3 heterostructures, enabled by a thermal-release-tape dry transfer process onto X-ray transparent silicon-rich nitride membranes. Under zero-field-cooled conditions, we observe robust bubble domain phases from 75 to 165 K, and across different number of folds of the multilayer Fe3GeTe2 Bi2Te3 heterostructures. This is in stark contrast with exfoliated single-crystal Fe3GeTe2 flakes, where ZFC stripe domains are observed for flakes thicker than 20 nm and no domains have been reported for thin flakes less than 15 nm. First-principles calculations and micromagnetic simulations reveal that interfacial coupling to Bi2Te3 modifies the magnetic anisotropy and introduces interfacial Dzyaloshinskii-Moriya interaction, shifting the magnetic phase space towards bubble-domain stabilization without field-cooling. Together, our results offer a new strategy for phase-selective control of magnetic domains through interfacial engineering.

cond-mat.mtrl-sci↗

arXiv2026

Ultra-Stable Weyl Topology Driven by Magnetic Textures in the Shandite Compound Co3Sn2S(2-x)Sex

We employ state-of-the-art first-principles calculations to investigate the shandite compounds Co3Sn2S2, Co3Sn2SeS, and Co3Sn2Se2, which host Weyl fermions and complex magnetic textures. Their magnetic structures are governed primarily by exchange interactions and magnetocrystalline anisotropy, whereas the symmetry-allowed alternating-layer Dzyaloshinskii-Moriya interaction (DMI) is found to be negligible. We identify a previously unrecognized spin-chiral interaction (SCI) arising from the kagome lattice topology, which plays a decisive role in stabilizing the experimentally observed magnetic textures. The extracted magnetic parameters reproduce experimental trends, with the SCI emerging as a novel and dominant contribution. The calculated SCI strengths are 0.78 meV, 0.86 meV, and 0.87 meV for Co3Sn2S2, Co3Sn2SeS, and Co3Sn2Se2, respectively. Furthermore, we demonstrate that short-wavelength magnetic textures drive phase transitions of the Weyl nodes, resulting in band flattening and the opening of an emergent gap. This newly identified SCI, together with the associated electronically driven phase transitions, provides a promising route for manipulating transport properties in spintronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Tuning Quantum States at Chirality-Reversed Planar Interface in Weyl Semimetals using an Interstitial Layer

The electronic band structure of Weyl semimetals possesses pairs of linear band crossings, called Weyl nodes, characterized by opposite chirality charges associated with each node. The momentum space position of the nodes can reverse across a planar interface and these host Fermi-arc-like bound states, in addition to scattering states. We show that a magnetic interstitial layer can tune these states in three distinct ways. The electrostatic potential and one of the in-plane magnetic potential components control the shape of the bound state Fermi-arcs. For moderate values of the same in-plane magnetic potential electrons are spin-filtered across the interface, while both the in-plane magnetic components and the electrostatic potential control the transmission of electrons. The ratio of in-plane to out-of-plane magnetic components can be used to turn on or turn off the magnetic potential effects, since the latter does not affect the interface states. The tunability arises from spin-momentum locking and chirality reversal at the interface. Thus, the effects can mix or interchange depending on the specific material but the states will remain tunable.

cond-mat.mes-hall↗

arXiv2024

Trends in hot carrier distribution for disordered noble-transition metal alloys

We developed and tested an approach for predicting trends for efficient hot carrier generation among disordered metal alloys. We provide a simple argument for the importance of indirect transitions in the presence of disorder, thus justifying the use of Joint Density of States (JDOS)-like quantities for exploring these trends. We introduce a new JDOS-like quantity, JDOSK, which heuristically accounts for longer lifetimes of quasiparticles close to the Fermi energy. To demonstrate the efficacy of this new quantity, we apply it to the study of Cu50X50 where X = Ag, Au, Pd and Y50Pd50 where Y = Au, Ni. We predict that Ni50Pd50 produces the most hot carriers among the alloys considered. The improvement in the density of excited photocarriers over the base alloy used, Cu50Ag50, is 3.4 times for 800 nm and 19 times for 1550 nm light. This boost in hot-carrier generation is consequence of the ferromagnetic nature of the Ni alloy. We argue that our method allows efficient material-specific predictions for low bias photoconductivity of alloys.

cond-mat.mtrl-sci↗

arXiv2023

On the classicality and uniqueness in loop quantization of Bianchi-I spacetimes

In loop quantum cosmology, ambiguities in the Hamiltonian constraint can result in models with varying phenomenological predictions. In the homogeneous isotropic models, these ambiguities were settled, and the improved dynamics was found to be a unique and phenomenologically viable choice. This issue has remained unsettled on the inclusion of anisotropies, and in the Bianchi-I model there exist two generalizations of isotropic improved dynamics. In the first of these, labelled as $\bar μ$ quantization, the edge length of holonomies depends on the inverse of the directional scale factor. This quantization has been favored since it results in universal bounds on energy density and anisotropic shear, and can be viably formulated for non-compact as well as compact spatial manifolds. However, there exists an earlier quantization, labelled as $\bar μ'$ quantization, where edge lengths of holonomies depend on the inverse of the square root of directional triads. This quantization is also non-singular and so far believed to yield a consistent physical picture for spatially compact manifolds. We examine the issue of the physical viability of these quantizations for different types of matter in detail by performing a large number of numerical simulations. Our analysis reveals certain limitations which have so far remained unnoticed. We find that while being non-singular, the $\bar μ'$ quantization suffers from a surprising problem where one of the triad components and associated polymerized term retains Planckian character even at large volumes. As a result, not only is the anisotropic shear not preserved across the bounce, which is most highlighted in the vacuum case, but the universe can exhibit an unexpected cyclic evolution. These problematic features are absent from the $\bar μ$ quantization leaving it as the only viable prescription for loop quantizing the Bianchi-I model.

gr-qc↗

arXiv2023

Bound states and controllable currents on Topological Insulator surfaces with extended magnetic defects

We show that a magnetic line defect on the surface of a topological insulator generically supports two distinct branches of spin-polarized and current carrying one-dimensional bound states. We identify the components of magnetic scattering that lead to the bound states. The velocity, and hence spin texture, of each of those branches can be independently tuned by a magnetic field rotated in the plane of the surface. We compute the local net and spin-resolved density of states as well as spin accumulation and charge currents. The net spin polarization and current due to both bound and scattering states vary stepwise as a function of the electrostatic and magnetic components of the scattering potential, and can be tuned by an applied field. We discuss stability of the bound states with respect to impurity scattering.

cond-mat.mes-hall↗

arXiv2020

Conductance of gated junctions as a probe of topological interface states

Energy dispersion and spin orientation of the protected states at interfaces between topological insulators (TIs) and non-topological materials depend on the charge redistribution, strain, and atomic displacement at the interface. Knowledge of these properties is essential for applications of topological compounds, but direct access to them in the interface geometry is difficult. We show that conductance of a gated double junction at the surface of a topological insulator exhibits oscillations and a quasi-linear decay as a function of gate voltage in different regimes. These give the values for the quasiparticle velocities along and normal to the junction in the interface region, and determine the symmetry of the topological interface states. The results are insensitive to the boundary conditions at the junction.

cond-mat.mes-hall↗

arXiv2016

Supermassive Black Holes from self-gravitating Bose-Einstein Condensates comprised of Ultra-light Bosonic Dark Matter

Observed active galactic nuclei at redshifts $\gtrsim 6$ suggest that supermassive black holes (SMBHs) had formed early on. Accretion of matter onto remnants of Population III stars leading to SMBHs is a very slow process, and therefore, such models encounter difficulties in explaining quasars detected at $ z \gtrsim 6$. In this paper, we invoke collapse of dark bosonic halo matter, existing initially in self-gravitating Bose-Einstein condensate (BEC) phase, to lead to formation of SMBH. Making use of Gross-Pitaevskii equation and employing a Gaussian trial wavefunction, we determine the time dependence of its parameters and thereby, track the time evolution of the wavefunction. If the condensate, made up of identical dark bosons of mass $m$, collapses to form a black hole of mass $M_{eff}$ as soon as the former's effective size shrinks below the corresponding Schwarzschild radius, a simple inequality $ m \ M_{eff} \gtrsim 0.64 \ m^2_{Pl} $ can be derived, that ensues from a competition between attractive self-gravity and quantum repulsion arising due to uncertainty principle. We show that formation of SMBHs takes place on dynamical time scales $\sim 10^8$ yrs. Existence of ultra-light ($m \sim 10^{-23} \ \mbox{eV}$) dark bosons not only can lead to SMBHs of mass $\sim 10^{12} \ M_\odot$ at $ z > 6$ but also such particles can masquerade both as dark matter as well as dark energy. Discovery of aligned radio-jets in the ELAIS-N1 GMRT deep field leads us to make simple estimates to demonstrate that vortices of a rotating BEC that collapse to form black holes can give rise to SMBHs with aligned spins on scales exceeding cluster size length scales, each with angular momentum $J \lesssim 3.6 \ n_W \frac {G M^2} {c}$, where $n_W$ and $M$ are the winding number and mass of a vortex, respectively.

gr-qc↗