Twisted Schwinger effect: Geometric effects in carrier creation in semimetals

Dirac and Weyl semimetals provide a testbed for studying nonperturbative geometric effects in laser field-induced electron dynamics [1]. There are several closely related but distinct geometric phenomena, i.e., (i) Floquet topological bands [2], (ii) dynamical Hall response due to the carrier motion [3], and (iii) pair creation [4]. In this talk, I will mainly focus on the phenomenon (iii).

Electron and hole pairs are created when strong laser fields irradiate a Dirac or Weyl semimetal. This is known as the Schwinger effect in the high-energy physics literature and is mathematically equivalent to the Landau-Zener breakdown in semiconductor physics. It is known that geometric effects also exist in nonadiabatic processes, which was first noticed by Berry in his paper [5]. We extend his analysis to second-order and apply it to the carrier creation in circularly polarized laser fields [4]. Our finding predicts a nonperturbative counterpart of the circular photogalvanic effect in 3D semimetals, which might be confirmed in a ultrafast pump-probe experiments.

[1] McIver et. al., Nature Physics 16 , 38 (2020).
[2] S. A. Sato, et al., Phys. Rev. B 99, 214302 (2019).
[3] TO, Aoki PRB79, 081406 (2009).
[4] S. Takayoshi, J. Wu, TO, arXiv:2005.01755.
[5] M. V. Berry, Proc. Roy. Soc. Lond. A 430, 405 (1990).