One of the most fundamental mysteries is the homochirality of living organisms on the Earth. Scientists have spent endless efforts in understanding the origin of the enantiomeric excess, in which a magneto-chiral effect is believed to play a role. However, this magneto-chiral effect observed so far is very weak in diamagnetic bulk crystals under a strong magnetic field, synthetic chiral molecules with magnetic components in solutions, or thin-film chiral magnets and metamaterials. Recently, atomically flat two-dimensional materials have emerged with intriguing properties such as optical anisotropy, two-dimensional ferromagnetism, and valley pseudospins. Here, we report the observation of giant magneto-chiral dichroism in atomically thin van der Waals crystals. We found such giant magneto-chiral dichroism originated from two unique physical processes. The parity-inversion symmetry breaking induces a large chirality, and time-reversal symmetry breaking results in strong magnetic moments. Such an approach offers rich physics with the interplay of the magnetism, chirality, and valley pseudospins in a unified manner. The observed giant magneto-chiral effect may further our understanding of the enantiomeric excess that is important for photochemical reactions, asymmetric synthesizes, and drug delivery.
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