Theory of nonperturbative photocurrent generation driven by quantum geometric effects

  Field-induced nonperturbative phenomena of quantum materials have attracted much attention with the development of laser technology, such as nonreciprocal responses and high-harmonic generation. The Landau-Zener tunneling (LZT), which exhibits a field-induced metal-insulator transition, is increasingly recognized as a key process underlying such nonperturbative phenomena. Recently, the geometric effects (Berry phase) associated with LZT have also become a topic of great interest. Among them, the nonreciprocal LZT exhibits a tunneling probability depending on the direction of the electric field; however, its experimental observation in solids remains to be achieved. 

  Here, we theoretically investigate the generation of photocurrent via nonreciprocal Landau-Zener tunneling based on the quantum Liouville equation. In particular, we focus on the geometric effects of the interference between electronic wave functions on the photocurrent induced by a pulsed laser field. By calculating the nonperturbative photocurrent, we find that its behavior can be controlled by tuning the carrier-envelope phase of the laser pulse. In this presentation, we demonstrate that this change in behavior originates from the geometric effects in the multitunneling process.