Magnetic polaronic exciton in A-type 2D van der Waals bulk material CrSBr

Abstract: 2D magnetic semiconductor CrSBr exhibits unique magneto-optical properties, yet its electronic structure and photophysical mechanisms remain unclear at high magnetic field and low temperature. Through comprehensive spectroscopic investigations, its charge-transfer band edge is identified at 500 nm. Below this band-edge, local excitonic magnetic polaronic states from Cr3+ ions out of FM aggregates in layer and bilayer could be seen due to phonon-spin-exciton coupling, in which magnetic polaronic PL1 emission occurs at 720 nm from single Cr3+ d-d transition, a dark-state pair exciton occurs at 850 nm in 10 K magnetic field, and double-peak PL2 emission at 920 nm out of Cr3+ FM trimer in monolayer is seen; besides, the magnetic bi-polaronic PL3 at 990 nm can be assigned to Cr3+ tetramers between FM adjacent layers. In magnetic field perpendicular to the layer, direct competition between PL1and dark-state excitons and PL2 and PL3 excitonic states persist in different temperatures. This study sheds light on the complicated magneto-exciton interactions in the multi-body effect of CrSBr, beneficial for quantum modulation in layered magnetic semiconductors.