Optical markers of magnetic phase transition in CrSBr

Abstract

Here, we investigate the role of the interlayer magnetic ordering of CrSBr in the framework of ab initio calculations and by using optical spectroscopy techniques.

Strong Exciton–Phonon Coupling as a Fingerprint of Magnetic Ordering in van der Waals Layered CrSBr

“…The change in the slope of the fwhm versus temperature occurs at about 140 K, indicating the presence of additional scattering centers below T N . In the AFM phase regime, scattering of excitons with incoherent magnons may further contribute to the broadening of the fwhm. , Above 140 K, the estimated values for Γ 0 , Γ L 0 , and ω L 0 are approximately 42, 26, and 14 meV, respectively. Importantly, the estimated energy of the longitudinal optical phonon ω L 0 agrees well with the phonon energy of A g 1 (118 cm –1 ), providing support for our assumptions about exciton–phonon coupling based on the photoluminescence results (at the current stage, theoretical modeling of the observed phenomenon is beyond our competence).…”

“…Based on these observations, we propose that the S-shaped dependence of the PL peak energy on temperature originates from competing effects of magnons and phonons on exciton energies. 29,33 Therefore, the shift in the PL peak position provides a valuable approach to investigate the magnetic properties of CrSBr at the micro-or even nanoscale, which can be challenging using conventional magnetometry techniques. Furthermore, the fwhm of the PL spectrum also exhibits unusual behavior as a function of temperature, similar to the integrated PL intensity and peak position.…”

“…Significantly, the threshold temperatures for the AFM and PM states coincide with the changes in PL emission as a function of temperature in the investigated CrSBr material. Based on these observations, we propose that the S-shaped dependence of the PL peak energy on temperature originates from competing effects of magnons and phonons on exciton energies. , Therefore, the shift in the PL peak position provides a valuable approach to investigate the magnetic properties of CrSBr at the micro- or even nanoscale, which can be challenging using conventional magnetometry techniques.…”

“…Figure c displays the Raman spectra obtained with an excitation laser energy of E L = 2.33 eV (λ = 532 nm) and polarization along the a and b axis, respectively. Structurally, CrSBr crystallizes similarly to FeOCl layered magnets, adopting an orthorhombic crystal structure within a Pmmn space group and a D 2h point group. ,− Within the first Brillouin zone, CrSBr is predicted to exhibit 18 phonon modes, including 15 optical modes and 3 acoustical branches . In back scattering geometry, with incident laser light perpendicular to the sample surface, the room-temperature Raman spectra of CrSBr reveal only three main optical phonons of A g symmetry.…”

Altermagnetic surface states: towards the observation and utilization of altermagnetism in thin films, interfaces and topological materials

“…31,32 Regarding the well-known antiferromagnetic 2D materials, we could not find any altermagnetism in the van der Waals system due to the high symmetry of these systems. [33][34][35] A usual structural distortion that lowers the symmetry in the van der Waals systems is due to the onedimensional spin Peierls instability, 36 however, the spin Peierls instability produces simple translations without rotations not leading to altermagnetism. Therefore, the simplest way to obtain altermagnetism in low dimensions is from thin films of 3D altermagnetic systems.…”