Magnetically correlated defects in a quasi-1D electronic van der Waals magnetic semiconductor

Defects in two-dimensional magnets are interesting objects to study with prospects for engineering magnetic properties at the atomic scale. The air-stable magnetic semiconductor CrSBr exhibits excellent optical properties providing opportunities to study defect physics in a magnetic environment.

Here, we show optically active defects in CrSBr that are correlated with the magnetic phase diagram. Optical emission properties in multilayer samples are excellent with 1 meV linewidth owing to a quasi-1D electronic structure. We study the defect density and type in scanning probe microscopy and characterize the emission properties in low-temperature photoluminescence (PL) and photoluminescence excitation spectroscopy. In magneto-PL, the defect emission energies are a fingerprint of the magnetic order, but with absolute shifts up to 100 times weaker than the exciton, further highlighting the layer-localized nature of the defect wave function. Moreover, a magnetic phase at low temperature correlates with a strong narrowing of the defect emission, suggesting a change in the spin of the involved bands of the defect transition.

We conclude that CrSBr is an exciting platform for investigating optically active defects that are correlated with the magnetic phase diagram. This opens several novel avenues for tailor-made complex magnetic phases with direct optical access.