Himani Mishra - Academia.edu (original) (raw)
Related Authors
University of the Basque Country, Euskal Herriko Unibertsitatea
Max Planck Institute for the Structure and Dynamics of Matter
Uploads
Papers by Himani Mishra
Physical Review B
We report here a giant |χ (2) baa | = 780 pm/V second harmonic and |χ (3) aaaa | = 1.4 × 10 −17 m... more We report here a giant |χ (2) baa | = 780 pm/V second harmonic and |χ (3) aaaa | = 1.4 × 10 −17 m 2 /V 2 third harmonic signal from single atomic sheet of buckled hexagonal GaAs. We demonstrate this through the solution of an ab initio real-time Bethe-Salpeter equation by including the electron-hole screened-exchange self-energy. The coupling between time-dependent external electric field and correlated electrons is treated within the modern theory of polarization. The result of our calculation envisage monolayer GaAs to be a prominent member in the material library for nonlinear signal generations.
Physical Review B
Using a fully ab-initio methodology, we demonstrate how the lattice vibrations couple with neutra... more Using a fully ab-initio methodology, we demonstrate how the lattice vibrations couple with neutral excitons in monolayer WSe2 and contribute to the non-radiative excitonic lifetime. We show that only by treating the electron-electron and electron-phonon interactions at the same time it is possible to obtain an unprecedented agreement of the zero and finite-temperature optical gaps and absorption spectra with the experimental results. The bare energies were calculated by solving the Kohn-Sham equations, whereas G0W0 many body perturbation theory was used to extract the excited state energies. A coupled electron-hole Bethe-Salpeter equation was solved incorporating the polaronic energies to show that it is the in-plane torsional acoustic phonon branch that contributes mostly to the A and B exciton build-up. We find that the three A, B and C excitonic peaks exhibit different behaviour with temperature, displaying different non-radiative linewidths. There is no considerable transition in the strength of the excitons with temperature but A-exciton exhibits darker nature in comparison to C-exciton. Further, all the excitonic peaks redshifts as temperature rises. Renormalization of the bare electronic energies by phonon interactions and the anharmonic lattice thermal expansion causes a decreasing band-gap with increasing temperature. The zero point energy renormalization (31 meV) is found to be entirely due to the polaronic interaction with negligible contribution from lattice anharmonicites. These findings may find a profound impact on electronic and optoelectronic device technologies based on these monolayers.
Physical Review B
We report here a giant zero-point energy renormalization of 273 meV in the direct band-gap at K i... more We report here a giant zero-point energy renormalization of 273 meV in the direct band-gap at K in the Brillouin zone and a 571 meV of blue-shifting in the position of the doubly-degenerate brightest excitonic peak in monolayer hexagonal boron nitride. The non-radiative exciton line-width is found to be 97 meV at 0 K with a large coupling strength of 1.1 eV. This line-width is found to be mainly dominated by the scattering from the longitudinal optical phonons near the degenerate LO-TO mode, with negligible contributions from other lower branches. Additionally, the band-gap has a temperature dependent slope of-0.53 meVK −1 , which we found to be in excellent agreement with the reported experimental data on large diameter boron nitride nanotubes. We obtained our results by solving a coupled electron-hole Bethe-Salpeter equation which includes the lattice vibrational dynamics, purely using an ab-initio approach.
Physical Review B
We report here a giant |χ (2) baa | = 780 pm/V second harmonic and |χ (3) aaaa | = 1.4 × 10 −17 m... more We report here a giant |χ (2) baa | = 780 pm/V second harmonic and |χ (3) aaaa | = 1.4 × 10 −17 m 2 /V 2 third harmonic signal from single atomic sheet of buckled hexagonal GaAs. We demonstrate this through the solution of an ab initio real-time Bethe-Salpeter equation by including the electron-hole screened-exchange self-energy. The coupling between time-dependent external electric field and correlated electrons is treated within the modern theory of polarization. The result of our calculation envisage monolayer GaAs to be a prominent member in the material library for nonlinear signal generations.
Physical Review B
Using a fully ab-initio methodology, we demonstrate how the lattice vibrations couple with neutra... more Using a fully ab-initio methodology, we demonstrate how the lattice vibrations couple with neutral excitons in monolayer WSe2 and contribute to the non-radiative excitonic lifetime. We show that only by treating the electron-electron and electron-phonon interactions at the same time it is possible to obtain an unprecedented agreement of the zero and finite-temperature optical gaps and absorption spectra with the experimental results. The bare energies were calculated by solving the Kohn-Sham equations, whereas G0W0 many body perturbation theory was used to extract the excited state energies. A coupled electron-hole Bethe-Salpeter equation was solved incorporating the polaronic energies to show that it is the in-plane torsional acoustic phonon branch that contributes mostly to the A and B exciton build-up. We find that the three A, B and C excitonic peaks exhibit different behaviour with temperature, displaying different non-radiative linewidths. There is no considerable transition in the strength of the excitons with temperature but A-exciton exhibits darker nature in comparison to C-exciton. Further, all the excitonic peaks redshifts as temperature rises. Renormalization of the bare electronic energies by phonon interactions and the anharmonic lattice thermal expansion causes a decreasing band-gap with increasing temperature. The zero point energy renormalization (31 meV) is found to be entirely due to the polaronic interaction with negligible contribution from lattice anharmonicites. These findings may find a profound impact on electronic and optoelectronic device technologies based on these monolayers.
Physical Review B
We report here a giant zero-point energy renormalization of 273 meV in the direct band-gap at K i... more We report here a giant zero-point energy renormalization of 273 meV in the direct band-gap at K in the Brillouin zone and a 571 meV of blue-shifting in the position of the doubly-degenerate brightest excitonic peak in monolayer hexagonal boron nitride. The non-radiative exciton line-width is found to be 97 meV at 0 K with a large coupling strength of 1.1 eV. This line-width is found to be mainly dominated by the scattering from the longitudinal optical phonons near the degenerate LO-TO mode, with negligible contributions from other lower branches. Additionally, the band-gap has a temperature dependent slope of-0.53 meVK −1 , which we found to be in excellent agreement with the reported experimental data on large diameter boron nitride nanotubes. We obtained our results by solving a coupled electron-hole Bethe-Salpeter equation which includes the lattice vibrational dynamics, purely using an ab-initio approach.