Electronic Structure Theory Group
Research Areas

First principles domain

  1. Excitonic interplay with phonons in bulk and nanoscale semiconductor materials
  2. Quasi harmonic analysis like thermal zero point energy computations, temperautre dependent lattice constants,  lattice anharmonicities
  3. Electrical mobilities in bulk and nanoscale semiconductor materials
  4. Nonlinear optical second and third harmonic generations in bulk and nanoscale semiconductor materials 
  5. Pump-probe and fluences excitonic spectroscopy in bulk and nanoscale semiconductor materials 
  6. Anamolous Hall effect, anisotropies from self-consistent Hubbard U in magnetic semiconductors and metals
  7. SMOKE and MOKE Kerr optical spectra from ferromagteic metals

Some latest work descriptions

We report here a giant ∣∣χ(2)baa∣∣=780 pm/V second harmonic and ∣∣χ(3)aaaa∣∣=1.4×10^−17m^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.

GaAs monolayer orbital contribution to band structure

Ground-state electron energy dispersion in monolayer-buckled GaAs in the absence of spin orbit coupling (SOC) demonstrating the partial density of states contributions from (a) px, (b) py, and (c) pz orbitals of As. The difference, Γ3v−Γ1v=−1.95eV, signifying a strong crystal-field splitting. In the presence of an SOC, the p-DOS contributions for (d) Ga 3S1/2, mj=±1/2, (e) As 4P3/2, mj=±1/2 and (f) As 4P3/2, mj=±3/2 are demonstrated. The presence of SOC makes Γ1v−Γcf4v=−0.11eV. At the Γ point, the valence spin-orbit splitting (Δ0=Γ5v−Γ4v) and the direct band-gap (E0=Γ1c−Γ5v) at Γ is 0.22 eV and 1.13 eV, respectively. EF is the Fermi energy and the top of the valence band is set to zero energy scale.

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Optical second harmonic generation (SHG) in monolayer GaAs

Nonlinear SHG spectra of ML buckled GaAs as function of laser frequencies. Panels (a, c, and e) are the SHG computed using IPA+scissor, TD-DFT, and TD-BSE level of theory, respectively (all are respective absolute values). Panels (b, d, and f) show the absorption spectra computed at ω and ω/2 under the IPA+scissor, TD-DFT, and TD-BSE level of theory, respectively. The open circles are the experimental SHG spectra of zincblende bulk GaAs taken from Bergfeld and Daum and put here for comparison with our monolayer structure. The solid and dashed vertical lines are for the ω and ω/2 gaps. The imaginary and real parts for each of the theory are also presented. From the imaginary part, one can see that SHG goes to zero below half of the band-gap in all the cases. All of these computations were performed on 72×72×1k-point grid.

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