Abstract

Two-dimensional semiconductors offer an exceptional platform for exploring new physical phenomena, combining simple electronic structures with the ability to fabricate high-quality, atomically thin devices. Among them, transition metal dichalcogenides (TMDs) such as WSe₂ have become central to studies of optical selection rules and valley physics.
In this talk, I will show how polarized photocurrent spectroscopy provides direct insight into the electronic structure, symmetry, and many-body interactions in 2D semiconductor devices. I will demonstrate how interfacial symmetry breaking at metal–semiconductor Schottky barriers influences both the response time and polarization selectivity of photodetectors, enabling sensitivity to circularly polarized light¹. To further enhance speed and responsivity, we use direct laser patterning to convert semiconducting MoTe₂ into its semimetallic phase, forming lateral all-2D heterostructures for integrated optoelectronic circuitry².
I will then discuss how crystalline anisotropy can be used to amplify polarization contrast in photocurrent measurements, using CrPS₄ as an example³. In this material, we observe dichroism in photocurrent that exceeding what is seen in optical reflectivity, highlighting the role of anisotropic charge transport. Finally, I will show how optical control of exciton–exciton interactions leads to nonlinear and polarization-dependent photocurrent responses. Using these measurements at high excitonic densities we are able to unveil the exciton-exciton scattering mechanisms and demonstrate control over many-body interactions through valley-selective excitation.
Our works demonstrate how we can engineer the valley-dependent responses of devices based on 2D materials and how the device symmetries can be engineered to optimize the contrast to polarized light. The polarization control over many-body interactions provides an additional tuning knob for quantum devices which rely on the exciton-exciton interaction, particularly devices exploiting excitonic condensates and spin-valley lasers, paving the way for new quantum photonic devices.

References
1. J. Quereda, et al., NPJ 2D Mater. and Appl. 5, 13 (2021).
2. J. Hidding, et al., ACS Photonics 11, 4083 (2024).
3. C.A. Cordero-Silis, et al., in preparation.
4. D. Vaquero, et al., in preparation.