Nonlinear optical process, including second harmonic generation and bulk photovoltaic effect, have attracted tremendous attention during the past few decades. For example, physicists and material scientists have pointed out that in a single system with broken inversion symmetry, static direct current can be obtained under light irradiation. This bulk photovoltaic (BPV) effect has been widely studied with the potential to overcome the Shockley–Queisser limit. Based on Kubo's perturbation theory, we evaluate BPV photoconductivity in a few ferroelectric/magnetic materials. In addition, our theoretical analyses and first-principles calculations reveal several hidden modes in BPV process, including spin current generation, layer-resolved currents, etc., which cannot be directly calculated from the overall bulk photovoltaic current. These research results could help us understand the connection between nonlinear optics and spintronics, and provide a theoretical basis for new information storage material carriers.

Jian Zhou, Professor at School of Materials Science and Engineering, Xi'an Jiaotong University. Zhou received Bc.S.(2008) and Ph.D.(2013) at Peking University in Theoretical Mechanics, followed by Postdoctoral Association position at Virginia Commonwealth University and Massachusetts Institute of Technology (2013-2018). His current research interests mainly focus on first-principles calculations of nonlinear optics of condensed matter materials, photoinduced material structures, and topological phase transitions. So far, he co-authored over 100 papers in PNAS, PRL, Nano Letters, etc. These papers have been cited more than 6,000 times, with an h-index of 33, and was selected as "Elsevier China Highly Cited Scholar". These works are sponsored by grants from the Chinese Young-Talent Program (Overseas) and National Natural Science Foundation of China.