Crsbr Exhibits Coupled Vibrational, Electronic, and Magnetic States at 1.96 eV Excitation

The interplay between light, magnetism, and atomic motion defines the behaviour of many advanced materials, and recent research focuses on understanding these connections in the van der Waals antiferromagnet CrSBr. Daria I. Markina, Priyanka Mondal, Lukas Krelle, and colleagues at the Institute for Condensed Matter Physics, TU Darmstadt, alongside Mikhail M. Glazov from the Ioffe Institute and Regine von Klitzing, demonstrate a strong coupling between vibrational modes, electronic excitations, and magnetic order within this material. Their investigation, employing advanced spectroscopic techniques, reveals how changes in atomic vibrations near the material’s magnetic transition point directly correlate with alterations in its electronic properties. This discovery establishes CrSBr as a promising material for exploring fundamental quasi-particle interactions and potentially developing novel technologies in areas such as spintronics and optical communication.

This research investigates these interactions using optical spectroscopy, including Raman scattering and reflectivity, to understand how these states couple and influence the material’s optical and magnetic properties, crucial for potential spintronic applications. Raman spectroscopy reveals several phonon modes, and their behaviour changes with temperature, indicating strong coupling between electrons and these vibrations. Reflectivity measurements map the material’s optical conductivity, identifying key electronic transitions and providing information about its band structure.

Magneto-optical measurements, performed in magnetic fields up to 9 Tesla, demonstrate the influence of magnetic ordering on the optical response, revealing signatures of magnetic excitations and spin-orbit interactions. The results demonstrate a strong coupling between the vibrational, electronic, and magnetic degrees of freedom in CrSBr, with certain phonon modes exhibiting anomalies near the magnetic ordering temperature, suggesting a direct coupling between lattice vibrations and magnetic order. By utilizing laser excitation energies of 1. 96 eV and 2. 33 eV, they induced distinct behaviours in the material’s Raman modes, systematically comparing results from a 5 nanometer thick sample region. Precise temperature control from 4 to 300 Kelvin was achieved using a cryostat and co-polarized measurement configuration.

This setup allowed meticulous tracking of changes in Raman scattering as a function of temperature and excitation wavelength, probing the connection between Raman modes, electronic states, and magnetization. The team observed that the polarization dependencies of the A2g and A3g Raman modes are strongly affected by temperature under 1. 96 eV excitation, with the a-axis component of the A2g mode growing significantly as temperature decreases. The A3g mode exhibited a similar evolution, exceeding the b-component intensity below the Nél temperature, marking the transition to a magnetically ordered state.

Measurements on regions of varying thickness, utilizing the b/a ratio as a parameter, revealed the behaviour of Raman modes. A fitting expression was developed to extract information from polar plots, describing the intensity of the Raman signal as a function of angle. Analysis revealed that the a-component of the A2g mode increased significantly under both 2. 33 eV and 1. 96 eV excitation, while the a-component of the A3g mode rose nearly fourfold under 1. 96 eV excitation, demonstrating a clear connection between the material’s magnetic phase transition and the behaviour of its Raman modes, establishing CrSBr as a versatile platform for exploring quasi-particle interactions in low-dimensional magnets.

Vibrational, Electronic, and Magnetic Coupling in CrSBr

The study of the van der Waals antiferromagnet CrSBr reveals a strong coupling between vibrational, electronic, and magnetic properties, providing insights into quasi-particle interactions within low-dimensional magnets. Researchers employed polarization-resolved Raman spectroscopy, complemented by optical absorption and photoluminescence excitation spectroscopy, to investigate these interactions across a broad temperature range, from 4 to 300 Kelvin. Experiments demonstrate that the A2g, A3g, and A1g Raman modes exhibit pronounced changes near the Nél temperature of 132 Kelvin, coinciding with modifications in excitonic transitions. Detailed measurements reveal that the polarization of Raman modes is sensitive to both excitation energy and temperature.

Under 2. 33 eV excitation, the A2g and A3g modes maintain relatively constant polarization down to approximately 80 Kelvin, with the A2g mode consistently aligned with the a-axis and the A3g mode with the b-axis. However, below 80 Kelvin, the A2g mode develops a slight four-fold symmetric component, while the A3g mode remains unchanged. In contrast, under 1. 96 eV excitation, both A2g and A3g modes show significant temperature-dependent polarization changes, with the a-axis component of the A2g mode becoming comparable in intensity as temperature decreases, and the A3g mode following a similar trend, exceeding the b-component below the Nél temperature.

Quantitative analysis of the Raman modes using a fitting expression reveals that the a-component of the A2g mode increased significantly under both 2. 33 eV and 1. 96 eV excitation, and the a-component of the A3g mode rose nearly fourfold under 1. 96 eV excitation. A distinct kink in the b-component appears near the Nél temperature for the A2g mode under 2. 33 eV excitation and for the A3g mode under 1. 96 eV excitation, suggesting that these modes couple to different electronic states selectively excited by varying laser energies, establishing CrSBr as a versatile platform for probing quasi-particle interactions and offering potential for advancements in communication technologies.

Excitonic-Phonon Coupling Drives Magneto-Optical Changes

Researchers have demonstrated a strong interplay between vibrational, electronic, and magnetic properties within the van der Waals antiferromagnet CrSBr, using advanced spectroscopic techniques. Temperature-dependent Raman spectroscopy, coupled with optical absorption measurements, reveals that the Raman modes of this material are sensitive to changes in its magnetic phase. Specifically, distinct polarization changes in the primary Raman modes were observed near the Néel temperature, coinciding with modifications in excitonic transitions, indicating that the connection between magnetic phase and phonon modes occurs.