The Influence of Defects on the Vibrational and Electronic Properties of the Quasi 1D van der Waals Magnet CrSBr

Abstract

The emergence of 2D semiconducting magnets offers exciting potential to explore low dimensional magnetism, magneto-electronic coupling, and the design of novel magnetic phases through defect engineering. The 2D semiconducting antiferromagnet CrSBr has generated recent attention because of its correlated magnetic, optical, and electronic properties, air stability, and quasi-1D electronic structure. In this thesis, we implement resonant Raman spectroscopy to explore the electron-phonon interactions in CrSBr. We find that the electron-phonon coupling is strongly polarized along the b-crystallographic axis, confirming the presence of a quasi-1D electronic structure. We then investigate the influence of defects on the vibrational and electronic properties of CrSBr through resonant Raman spectroscopy of flakes irradiated with helium ions. The defective Raman spectra of CrSBr can be understood through the phonon confinement model, and we identify the emergence of two defect modes. These modes are also strongly polarized along the b-axis and are enhanced by resonant Raman spectroscopy. Remarkably, we find that the polarization response is preserved even at high defect concentrations, indicating that the electronic structure of CrSBr is highly robust. Finally, we exfoliate four additional air-stable 2D magnets with a MOCl (M = Ti, V, Fe, Cr) composition, which we believe may also have similar advantageous properties as CrSBr.