SciPost Phys. 11, 075 (2021) ·
published 12 October 2021
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We study the tunneling mechanism of nonlinear optical processes in
solids induced by strong coherent laser fields.
The theory is based on an extension of the
Landau-Zener model with nonadiabatic geometric effects.
In addition to the
rectification effect known previously, we find two effects, namely
perfect tunneling
and counterdiabaticity at fast sweep speed.
We apply this theory to the
twisted Schwinger effect, i.e., nonadiabatic pair production of particles
by rotating electric fields, and
find a nonperturbative generation mechanism of the
opto-valley polarization and photo-current
in Dirac and Weyl fermions.
