arXiv subjects

Sanjay K Banerjee

Publications and source records attributed to Sanjay K Banerjee.

5 recordsLinked to original sources

arXiv2025

Three-Dimensional Electrostatic and Quantum-Confinement Modeling of Silicon Nanowire Double Quantum Dots

We present a three-dimensional simulation study of silicon nanowire double quantum dots (DQDs) with leads at T = 2 K, which extends beyond traditional effective mass or quasi-1D and quasi-2D approaches typically applied to bulk or planar geometries. A 3-D Poisson solver is self-consistently coupled to 2-D Schrodinger along slices normal to transport (width * thickness) to obtain spatially varying subbands and wavefunctions at T = 2 K. The slice approximation is justified by the large aspect ratio (Ltot/W > 20) and by the small (< 1.2 percent) wavefunction variation observed along the transport direction. The resulting effective conduction-band profile is imported into a full-wave, open-boundary Schrodinger solver to compute the transmission spectrum T(E), and the tunnel coupling (tc) is evaluated from the bonding and antibonding splitting of the first two resonances in T(E). The simulations show that narrow dots (W = 5 nm) provide strong confinement and robust single-electron localization but require higher plunger-gate voltage, whereas wider dots (W = 20 nm) load electrons at lower bias but form shallower, more delocalized states. The tunnel coupling decreases as the dot width and length are increased, due to the reduced wavefunction overlap between the dots, and saturates once W > 2LPG, when longitudinal confinement is dominated by the plunger gate length. The simulated tunnel coupling trend agrees with experimental data reported for the Si DQD device.

cond-mat.mes-hall↗

arXiv2020

Structural and Magnetic Properties of Molecular Beam Epitaxy Grown Chromium Selenide Thin Films

Chromium selenide thin films were grown epitaxially on Al${_2}$O${_3}$(0001) and Si(111)-(7${\times}$7) substrates using molecular beam epitaxy (MBE). Sharp streaks in reflection high-energy electron diffraction and triangular structures in scanning tunneling microscopy indicate a flat smooth film growth along the c-axis, and is very similar to that from a hexagonal surface. X-ray diffraction pattern confirms the growth along the c-axis with c-axis lattice constant of 17.39 Å. The grown film is semiconducting, having a small band gap of about 0.034 eV, as calculated from the temperature dependent resistivity. Antiferromagnetic nature of the film with a Néel temperature of about 40 K is estimated from the magnetic exchange bias measurements. A larger out-of-plane exchange bias, along with a smaller in-plane exchange bias is observed below 40 K. Exchange bias training effects are analyzed based on different models and are observed to be following a modified power-law decay behavior.

cond-mat.mtrl-sci↗

arXiv2019

Rational design principles for giant spin Hall effect in 5d-transition metal oxides

Spin Hall effect (SHE), a mechanism by which materials convert a \textit{charge} current into a \textit{spin} current, invokes interesting physics and promises to empower transformative, energy-efficient memory technology. However, fundamental questions remain about the essential factors that determine SHE. Here we solve this open problem, presenting a comprehensive theory of five \textit{foundational factors} that control the value of intrinsic SHE in transition metal oxides. Arising from our key insight regarding the inherently geometric nature of SHE, we demonstrate that two of these factors are crystal field strength and structural distortions. Moreover, we discover that a new class of materials (anti-perovskites) promises to demonstrate \textit{giant} SHE, that is an order of magnitude larger than that reported for any oxide. We derive three other factors that control SHE and demonstrate the nuanced role of electron correlations. Our findings bring deeper insight into the physics driving SHE, and could help enhance, as well as, externally control SHE values.

cond-mat.mtrl-sci↗

arXiv2019

The microscopic origin of DMI in magnetic bilayers and prediction of giant DMI in new bilayers

Skyrmions are widely regarded as promising candidates for emergent spintronic devices. Dzyaloshinskii-Moriya interaction (DMI) is often critical to the generation and manipulation of skyrmions. However, there is a fundamental lack of understanding of the origin of DMI or the mechanism by which DMI generates skyrmions in magnetic bilayers. Very little is known of the material parameters that determine the value of DMI. This knowledge is vital for rational design of skyrmion materials and further development of skyrmion technology. To address this important problem, we investigate DMI in magnetic bilayers using first-principles. We present a new theoretical model that explains the microscopic origin of DMI in magnetic bilayers. We demonstrate that DMI depends on two parameters, interfacial hybridization and orbital contributions of the heavy metal. Using these parameters, we explain the trend of DMI observed. We also report four new materials systems with giant DMI and new designs for magnetic multilayers that are expected to outperform the best materials known so far. Our results present a notably new understanding of DMI, uncover highly promising materials and put forth novel pathways for the controlled generation of skyrmions.

cond-mat.mtrl-sci↗

arXiv2017

Angular dependence of magnetization reversal in epitaxial chromium telluride thin films with perpendicular magnetic anisotropy

We investigate magnetic anisotropy and magnetization reversal mechanism in chromium telluride thin films grown by molecular beam epitaxy. We report existence of strong perpendicular anisotropy in these thin films, along with a relatively strong second order anisotropy contribution. The angular variation of the switching field observed from the magnetoresistance measurement is explained quantitatively using a one-dimensional defect model. The model reveals the relative roles of nucleation and pinning in the magnetization reversal, depending on the applied field orientation. Micromagnetic simulations are performed to visualize the domain structure and switching process.

cond-mat.mes-hall↗