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Excitonic effects in optical-field-driven quasi 2D materials from time-dependent GW approach

Invited

Abstract

Atomically thin quasi two-dimensional (2D) insulating materials exhibit novel exciton physics due to ineffective screening, quantum confinement, and topological effects. Such exciton physics has recently been studied in details experimentally and theoretically. Going beyond near-equilibrium, one expects that excitonic effects also dominate the responses of out-of-equilibrium systems and can lead to interesting phenomena in optically-driven 2D materials. Using a newly developed real-time, non-equilibrium Green function method within the adiabatic GW approximation, we show that, for non-centrosymmetric 2D semiconductors, excitonic effects give rise to a strong DC current, the so-called shift current, upon even sub-bandgap frequency CW light illumination through a second-order nonlinear optical process. The frequency-dependent shift current coefficients can be enhanced by orders of magnitude by the strong e-h interactions, producing a bulk photovoltaic effect (i.e., without having to have a p-n junction) of promise for applications with appropriate materials. Furthermore, we show that, in optical-field-driven angle-resolved photoemission spectroscopy (ARPES) experiments, the energy and wavefunction of excitons may be measured directly under achievable laboratory conditions. With optical pump frequencies close to the resonance frequency for exciton excitations, distinct excitonic features manifest as modulated replicas of the involved valence band states. Alos, at higher pump intensity, the quasiparticle band energies are renormalized due to the driving optical fields.

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Presenters

  • Yang-hao Chan

    Lawrence Berkeley National Laboratory, University of California at Berkeley and Lawrence Berkeley National Laboratory, University of California, Berkeley, Department of physics, University of California at Berkeley, Berkeley, California

Authors

  • Yang-hao Chan

    Lawrence Berkeley National Laboratory, University of California at Berkeley and Lawrence Berkeley National Laboratory, University of California, Berkeley, Department of physics, University of California at Berkeley, Berkeley, California

  • Diana Qiu

    Yale University, Department of Mechanical Engineering and Materials Science, Yale University, Mechanical Engineering and Materials Science, Yale University, School of Engineering and Applied Physics, Yale University

  • Felipe Da Jornada

    Stanford University, Materials Science and Engineering, Stanford University, Department of Materials Science and Engineering, Stanford University, Stanford Univ, Department of Materials Science and Engineering, Stanford University, Stanford, California

  • Steven G Louie

    University of California, Berkeley, Department of Physics, University of California, Berkeley, University of California at Berkeley and Lawrence Berkeley National Laboratory, UC Berkeley & Lawrence Berkeley National Laboratory, University of California at Berkeley, and Lawrence Berkeley National Laboratory, Lawrence Berkeley National Laboratory, Department of physics, University of California at Berkeley, Berkeley, California