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arXiv · 2504.06150

Direct measurement of broken time-reversal symmetry in centrosymmetric and non-centrosymmetric atomically thin crystals with nonlinear Kerr rotation

Florentine Friedrich·Paul Herrmann·Shridhar Sanjay Shanbhag·Sebastian Klimmer·Jan Wilhelm·Giancarlo Soavi
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Abstract

Time-reversal symmetry, together with space-inversion symmetry, is one of the defining properties of crystals, underlying phenomena such as magnetism, topology and non-trivial spin textures. Transition metal dichalcogenides (TMDs) provide an excellent tunable model system to study the interplay between time-reversal and space-inversion symmetry, since both can be engineered on demand by tuning the number of layers and via all-optical bandgap modulation. In this work, we modulate and study time-reversal symmetry using third harmonic Kerr rotation in mono- and bilayer TMDs. By illuminating the samples with elliptically polarized light, we achieve spin-selective bandgap modulation and consequent breaking of time-reversal symmetry. The reduced symmetry modifies the nonlinear susceptibility tensor, causing a rotation of the emitted third harmonic polarization. With this method, we are able to probe broken time-reversal symmetry in both non-centrosymmetric (monolayer) and centrosymmetric (bilayer) crystals. Furthermore, we discuss how the detected third harmonic rotation angle directly links to the spin-valley locking in monolayer TMDs and to the spin-valley-layer locking in bilayer TMDs. Thus, our results define a powerful approach to study broken time-reversal symmetry in crystals regardless of space-inversion symmetry, and shed light on the spin, valley and layer coupling of atomically thin semiconductors.

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Florentine Friedrich, Paul Herrmann, Shridhar Sanjay Shanbhag, Sebastian Klimmer, Jan Wilhelm, Giancarlo Soavi. 2025-04-08. Direct measurement of broken time-reversal symmetry in centrosymmetric and non-centrosymmetric atomically thin crystals with nonlinear Kerr rotation. https://doi.org/10.1038/s41566-025-01801-2

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