Enhanced photovoltaic effect in symmetry-engineered van der Waals nanostructures

Second-order nonlinear transport, which is the intrinsic rectification effect reflecting the symmetry breaking in solids, has been recently recognized as not only a unique functionality of noncentrosymmetric systems but also a sophisticated probe of band geometry/topology [1].

In this talk, I will especially focus on the second-order nonlinear transport induced by photoirradiation in symmetry-engineered van der Waals nanostructures [2,3]. The giant bulk photovoltaic effect, which indicates the emergence of photo-induced spontaneous current without conventional semiconductor p-n junction nor bias voltage, was observed in van der Waals nanostructures with reduced symmetry such as WS₂ nanotubes [2] and WSe₂/Black phosphorus heterointerfaces [3]. Observed characteristic behaviors of the bulk photovoltaic effect can be well interpreted by the shift current mechanism, which is a quantum geometric photocurrent originated from the shift of the wave packet under the light illumination.

The present results offer a simple and powerful guideline for controlling the symmetry and band geometry/topology of nanomaterials and also provide the concept of electronic polarization and resultant emergent physical properties in complex nanostructures.