arXiv subjects

Raj Kumar Paudel

Publications and source records attributed to Raj Kumar Paudel.

3 recordsLinked to original sources

arXiv2025

Brightening interlayer excitons by electric-field-driven hole transfer in bilayer WSe2

We observe the interlayer A1s^I, A2s^I, and B1s^I excitons in bilayer WSe2 under applied electric fields using reflectance contrast spectroscopy. Remarkably, these interlayer excitons remain optically bright despite being well separated from symmetry-matched intralayer excitons-a regime where conventional two-level coupling models fail unless unphysically large coupling strengths are assumed. To uncover the origin of this brightening, we perform density functional theory (DFT) calculations and find that the applied electric field distorts the valence-band Bloch states, driving the hole wavefunction from one layer to the other. This field-driven interlayer hole transfer imparts intralayer character to the interlayer excitons, thereby enhancing their oscillator strength without requiring hybridization with bright intralayer states. Simulations confirm that this mechanism accounts for the major contribution to the observed brightness, with excitonic hybridization playing only a minor role. Our results identify interlayer hole transfer as a robust and general mechanism for brightening interlayer excitons in bilayer transition metal dichalcogenides (TMDs), especially when inter- and intralayer excitons are energetically well separated.

cond-mat.mes-hall↗

arXiv2025

Semi-empirical Pseudopotential Method for Monolayer Transition Metal Dichalcogenides

We present a semi-empirical pseudopotential method for accurately computing the band structures and bloch states of monolayer transition metal dichalcogenides(TMDCs), including MoS2, MoSe2, WS2, and WSe2. Our approach combines local and nonlocal pseudopotentials, carefully fitted to reproduce fully self-consistent density-functional theory results while using only a minimal set of empirical parameters. By expressing the total potential as a sum of a few separable components, we achieve both accuracy and computational efficiency. The transferability of the monolayer-fitted pseudopotentials is assessed through a direct application to bilayer TMDCs without additional refitting, where good agreement with self-consistent DFT band structures is obtained near the band edges. The resulting framework provides an efficient and flexible platform for band-structure and Bloch-state calculations in TMDC-based low-dimensional materials. Keywords: transition metal dichalcogenides, semi-empirical pseudopotentials, density functional theory, electronic structure, computational physics

cond-mat.mtrl-sci↗

arXiv2024

Efficient Band Structure Calculation for Transitional-Metal Dichalcogenides Using the Semiempirical Pseudopotential Method

The Semiempirical Pseudopotential Method (SEPM) has emerged as a valuable tool for accurately determining band structures, especially in the realm of low-dimensional materials. SEPM operates by utilizing atomic pseudopotentials, which are derived from DFT calculations. SEPM calculations offer a unique advantage compared to DFT as they eliminate the requirement for iterative self-consistent solutions in solving the Schrödinger equation, leading to a substantial reduction in computational complexity. The incorporation of both non-local and local Semiempirical Pseudopotentials in our current approach yields band structures and wavefunctions with enhanced precision compared to traditional empirical methods. When applied to monolayer TMDCs, adjusting the parameters to align with pertinent values obtained from DFT computations enables us to faithfully replicate the band structure, opening avenues for investigating the optoelectronic properties of TMDCs and exploring their potential applications in nanodevices.

cond-mat.mtrl-sci↗