arXiv subjects

Aditya Dey

Publications and source records attributed to Aditya Dey.

8 recordsLinked to original sources

arXiv2025

Strain-induced Moir\'e Reconstruction and Memorization in Two-Dimensional Materials without Twist

Two-dimensional (2D) materials with a twist between layers exhibit a moir\'e interference pattern with larger periodicity than any of the constituent layer unit cells. In these systems, a wealth of exotic phases appear that result from moir\'e-dependent many-body electron correlation effects or non-trivial band topology. One problem with using twist to generate moir\'e interference has been the difficulty in creating high-quality, uniform, and repeatable samples due to fabrication through mechanical stacking with viscoelastic stamps. Here we show, a new method to generate moir\'e interference through the controlled application of layer-by-layer strain (heterostrain) on non-twisted 2D materials, where moir\'e interference results from strain-induced lattice mismatch without twisting or stacking. Heterostrain generation is achieved by depositing stressed thin films onto 2D materials to apply large strains to the top layers while leaving layers further down less strained. We achieve deterministic control of moir\'e periodicity and symmetry in non-twisted 2D multilayers and bilayers, with 97% yield, through varying stressor film force (film thickness X film stress) and geometry. Moir\'e reconstruction effects are memorized after the removal of the stressor layers. Control over the strain degree-of-freedom opens the door to a completely unexplored set of unrealized tunable moir\'e geometric symmetries, which may now be achieved in a high-yield and user-skill independent process taking only hours. This technique solves a long-standing throughput bottleneck in new moir\'e quantum materials discovery and opens the door to industrially-compatible manufacturing for 2D moir\'e-based electronic or optical devices.

cond-mat.mtrl-sci↗

arXiv2025

HADL Framework for Noise Resilient Long-Term Time Series Forecasting

Long-term time series forecasting is critical in domains such as finance, economics, and energy, where accurate and reliable predictions over extended horizons drive strategic decision-making. Despite the progress in machine learning-based models, the impact of temporal noise in extended lookback windows remains underexplored, often degrading model performance and computational efficiency. In this paper, we propose a novel framework that addresses these challenges by integrating the Discrete Wavelet Transform (DWT) and Discrete Cosine Transform (DCT) to perform noise reduction and extract robust long-term features. These transformations enable the separation of meaningful temporal patterns from noise in both the time and frequency domains. To complement this, we introduce a lightweight low-rank linear prediction layer that not only reduces the influence of residual noise but also improves memory efficiency. Our approach demonstrates competitive robustness to noisy input, significantly reduces computational complexity, and achieves competitive or state-of-the-art forecasting performance across diverse benchmark datasets. Extensive experiments reveal that the proposed framework is particularly effective in scenarios with high noise levels or irregular patterns, making it well suited for real-world forecasting tasks. The code is available in https://github.com/forgee-master/HADL.

cs.LG↗

arXiv2023

Strain Engineering for High-Performance Phase Change Memristors

A new mechanism for memristive switching in 2D materials is through electric-field controllable electronic/structural phase transitions, but these devices have not outperformed status quo 2D memristors. Here, we report a high-performance bipolar phase change memristor from strain engineered multilayer 1T'-MoTe$_{2}$ that now surpasses the performance metrics (on/off ratio, switching voltage, switching speed) of all 2D memristive devices, achieved without forming steps. Using process-induced strain engineering, we directly pattern stressed metallic contacts to induce a semimetallic to semiconducting phase transition in MoTe2 forming a self-aligned vertical transport memristor with semiconducting MoTe$_{2}$ as the active region. These devices utilize strain to bring them closer to the phase transition boundary and achieve ultra-low ~90 mV switching voltage, ultra-high ~10$^8$ on/off ratio, 5 ns switching, and retention of over 10$^5$ s. Engineered tunability of the device switching voltage and on/off ratio is also achieved by varying the single process parameter of contact metal film force (film stress $\times$ film thickness).

physics.app-ph↗

arXiv2023

An atomistic insight into moiré reconstruction in Twisted Bilayer Graphene beyond the magic angle

Twisted bilayer graphene exhibits electronic properties that are highly correlated with the size and arrangement of moiré patterns. While rigid rotation of two layers creates the topology of moiré patterns, local rearrangements of the atoms due to interlayer van der Waals interactions result in atomic reconstruction within the moiré cells. The ability to manipulate these patterns by controlling twist angle and/or externally applied strain provides a promising route to tune their properties. While this phenomenon has been extensively studied for angles close to or smaller than the magic angle (θm=1.1°), its extent for higher angles and how it evolves with strain is unknown and is believed to be mostly absent at high angles. We use theoretical and numerical analyses to resolve reconstruction in angles above θm using interpretive and fundamental physical measures. In addition, we propose a method to identify local regions within moiré cells and track their evolution with strain for a range of representative high twist angles. Our results show that reconstruction is actively present beyond the magic angle and its contribution to the evolution of the moiré cells is major. Our theoretical method to correlate local and global phonon behavior provides further validation on the role of reconstruction at higher angles. Our findings provide a better understanding of moiré reconstruction in large twist angles and the evolution of moiré cells in the presence of strain, that might be very crucial for twistronics-based applications.

cond-mat.mtrl-sci↗

arXiv2023

Moiré Engineering in 2D Heterostructures with Process-Induced Strain

We report deterministic control over moiré superlattice interference pattern in twisted bilayer graphene by implementing designable device-level heterostrain with process-induced strain engineering, a widely used technique in industrial silicon nanofabrication processes. By depositing stressed thin films onto our twisted bilayer graphene samples, heterostrain magnitude and strain directionality can be controlled by stressor film force (film stress x film thickness) and patterned stressor geometry, respectively. We examine strain and moiré interference with Raman spectroscopy through in-plane and moiré-activated phonon mode shifts. Results support systematic C$_{3}$ rotational symmetry breaking and tunable periodicity in moiré superlattices under the application of uniaxial or biaxial heterostrain. Experimental results are validated by molecular statics simulations and density functional theory based first principles calculations. This provides a method to not only tune moiré interference without additional twisting, but also allows for a systematic pathway to explore different van der Waals based moiré superlattice symmetries by deterministic design.

cond-mat.mes-hall↗

arXiv2020

First principles study of optical and tunable electronic properties of crystalline Li2TeO3

The optical and electronic properties of crystalline Li2TeO3, which is a tellurite glass, is studied in the framework of density functional theory (DFT) implemented software SIESTA. The material has monoclinic symmetrized structure and the unit or primitive cell of the material, periodic in all directions has been taken to study the properties. The electronic structures show that it is a wide-gap semiconductor and the property changes to metallic when subjected to electric field. This tunable property can be used in various fields of electronics. The optical properties studied tells that Li2TeO3 can be a promising material to be used as a hole transport material (HTM) for developing efficient perovskite solar cell including other applications as well.

cond-mat.mtrl-sci↗

arXiv2020

Modulating the electronic and optical properties of a ternary chalcogenide CdTl2Te4 via external electric field: A DFT study

Various ternary chalcogenide systems and their properties are one of the hot topics for researchers nowadays. In this article, one of the ternary chalcogenide compounds, CdTl2Te4 is studied including its electronic structures and optical properties via first principles calculations using SIESTA code. The structure of the compound has a tetragonal crystal system and the unit cell is periodic in all directions. The band structure showed it is a direct band gap semiconductor which is explained by the density of states. The energy gap obtained is seen to increase on employing external electric field perpendicular to the xy plane, but does not increase on increasing the magnitude of field strength. The optical properties which includes absorption coefficient, reflectance, real & imaginary parts of dielectric function, refractive index and extinction coefficient were calculated for polarized light both in plane and out of the plane, but the interesting modulation in properties were seen for the latter which can open up applications of the compound in UV absorbers, making solar cells, etc. So, the compound being a narrow-gap semiconductor along with its tunable electronic and optical properties can have potential application in the fields such as optoelectronics.

cond-mat.mtrl-sci↗

arXiv2020

Ab-initio calculations of magnetic and optical properties of 3x3 supercell of TiX$_2$ (X = S, Se and Te) compounds under the effect of externally applied electric field and strain

The magnetic and optical properties of titanium dichalcogenide compounds, TiX$_2$ (X = S, Se and Te) have been calculated by first principles calculations using density functional theory (DFT) as implemented in SIESTA code. A 3x3 supercell of the compounds is taken in this study to be able to tune the properties obtained from the unit cell of these compounds. With magnetic states (ferromagnetic nature) as the attained ground state, spin polarized calculations are performed to obtain the mentioned properties. Further, with spin polarization into effect, external electric field (along z-direction) and biaxial strain (along x and y-directions) is employed to study their effect on these properties. The effect of biaxial strain on the geometry of the compounds is also studied. It is observed that the pristine supercell of the compounds possess a good amount of magnetic moment and this can be modulated using the applied field and strain. For the optical properties, polarized light along the z-direction (c axis) is used. These properties include the calculation of real & imaginary parts of dielectric function, absorption coefficient, reflectance, optical conductivity and refractive index in 0-25 eV energy range. Various modulations of these properties are observed including the blue-shifts and red-shifts of energies with highest peaks in the visible region and also shifting of energies to other regions of the electromagnetic spectrum. Hence, with the tunable magnetic and diverse optical properties, the compounds can be useful in the field of spintronics and in making various optical devices.

cond-mat.mtrl-sci↗