Magnetic Polaronic Exciton in A-Type 2D van der Waals Bulk Material CrSBr

Abstract

Two-dimensional van der Waals magnetic semiconductors offer unprecedented opportunities to explore coupled magnetic and excitonic phenomena. Through femtosecond transient absorption spectroscopy and density functional theory calculations, we identify the charge-transfer band edge in CrSBr near 500 nm (2.48 eV) and correlate distinct photoluminescence (PL) channels with Cr³⁺ coordination environments. Temperature-dependent measurements reveal that 720 nm emission (PL₁) persists across all temperatures, consistent with isolated Cr³⁺ centers; ∼920 nm emission (PL₂) intensifies near the ferromagnetic (FM) transition (140 K); and 990 nm emission (PL₃) appears only in thick samples below the antiferromagnetic (AFM) transition (132 K). Under strong perpendicular magnetic fields with 488 nm excitation, we observe a dark-state exciton at ∼850 nm, with anticorrelated intensity variations between PL₁/dark-state and PL₂/PL₃, demonstrating field-tuned energy redistribution. These findings establish magnetic polaronic excitons in van der Waals semiconductors and enable manipulation of excitonic properties through magnetic order control.