Enhanced Valley Polarization via Nonlinear Cascaded Quantum-Geometric Selection Rules
Abstract
The quantum geometric properties of Bloch electrons fundamentally govern light-matter interactions and optical selection rules in solids. In semiconducting transition-metal dichalcogenides, circularly polarized excitation near the band edge enables valley-selective interband transitions, providing the basis for valleytronics. While nonlinear optical protocols are being developed to manipulate and probe valley selection rules, they largely rely on band-edge transitions that proceed via virtual intermediate states. Here, we demonstrate a doubly resonant cascaded nonlinear pathway from the valence band to high-lying states, mediated by a real intermediate state whose participation substantially reshapes the valley optical selection rules. Using time- and angle-resolved extreme-ultraviolet photoemission spectroscopy in combination with a time-dependent Lindblad master-equation formalism, we show that this cascaded nonlinear photoexcitation produces a substantially enhanced high-lying valley polarization compared to the conventional linear optical response near the band edge. The extension of the quantum-geometry-based selection rules to the nonlinear regime and high-lying bands offers new perspectives for ultrafast valleytronics and should play a determinant role in strong-field-driven phenomena in quantum materials.
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Cite
@article{arxiv.2605.03663,
title = {Enhanced Valley Polarization via Nonlinear Cascaded Quantum-Geometric Selection Rules},
author = {Quentin Courtade and Sotirios Fragkos and Dominique Descamps and Stéphane Petit and Yann Mairesse and Michael Schüler and Samuel Beaulieu},
journal= {arXiv preprint arXiv:2605.03663},
year = {2026}
}