Sensing the Local Magnetic Environment through Optically Active Defects in a Layered Magnetic Semiconductor

Abstract

Atomic-level defects in van der Waals (vdW) materials are essential building blocks for quantum technologies and quantum sensing applications. The layered magnetic semiconductor CrSBr is an outstanding candidate for exploring optically active defects because of a direct gap, in addition to a rich magnetic phase diagram, including a recently hypothesized defect-induced magnetic order at low temperature. Here, we show optically active defects in CrSBr that are probes of the local magnetic environment. We observe a spectrally narrow (1 meV) defect emission in CrSBr that is correlated with both the bulk magnetic order and an additional low-temperature, defect-induced magnetic order. We elucidate the origin of this magnetic order in the context of local and nonlocal exchange coupling effects. Our work establishes vdW magnets like CrSBr as an exceptional platform to optically study defects that are correlated with the magnetic lattice. We anticipate that controlled defect creation allows for tailor-made complex magnetic textures and phases with direct optical access.

The Bulk van der Waals Layered Magnet CrSBr is a Quasi-1D Material

“…This is not just a simple surface effect since we do not observe this structural distortion in STM topographic images (see inset Figure 1i). 36 Importantly, this coincides with the direction of the strong quasi-1D electronic structure of CrSBr (see Figure 1g). We further visualize and quantify this structural distortion by analyzing the percentage change in the interatomic lattice distance Δb (see Methods) between neighboring Cr and S/Br atomic columns along the b direction (see Figure 2c,d).…”

“…6−8 While the observation of a Fano line shape is surprising in a semiconductor like CrSBr, this is not limited to metallic systems like CNTs but this phenomenon is also observed in gapped materials that generally exhibit pronounced electron−phonon interactions. 50,51 CrSBr has shown a high intrinsic carrier concentration of ∼10 13 cm −237 in agreement with a high concentration of Br vacancy defects 36 that induce n-doping in the material, which shifts the Fermi level close to the conduction band. Moreover, low-dimensional behavior and Fano physics 52 have also been observed in TiOCl, thereby suggesting that this is likely a universal effect in materials that are of FeOCl-type.…”

“…29,31 It is also an A-type antiferromagnet (AFM) with the magnetic easy axis along the b direction and a high Neél temperature of T N ∼ 132 K. 28,31 Significantly, CrSBr is a relatively stable material in air. 39 Recent works have shown structural phase transformations, 35 correlated magneto-optical 33,36,39 and magnetotransport 31,37,38 properties, and the coupling of excitons and magnons. 40 Moreover, a recent transport study has reported an unusual anisotropy in the electron conductivity along the a and b directions of CrSBr with striking ratios of up to 10 5 , attributed to quasi-1D transport.…”

Probing Defects and Spin‐Phonon Coupling in CrSBr via Resonant Raman Scattering

“…This suggests that chromium is not fully removed but rather displaced into interstitial positions also in agreement with a high defect formation energy. [35] Going to high He + doses (σ > 10 15 cm −2 ), we furthermore detect one broad band at ≈ 90 − 100 cm −1 , labeled as D*. While both D1 and D* emerge near the A g 1 mode, they appear to be distinct defect signatures.…”

“…[30,31] The combination of magnetic and semiconducting properties manifests in correlated magneto-transport [30,32] and magneto-optical effects. [31,[33][34][35] CrSBr also shows strongly anisotropic electronic transport in multilayers [36] due to its quasi-1D electronic structure and weak interlayer hybridization. [31] Moreover, a defect-induced magnetic order is observed in magneto-transport [32] and magnetometry measurements.…”