Magnetic-Field-Dependent Electron-Orbital-Phonon Coupling in Layered vdW PdSe₂ Flakes Revealed by Helicity-Resolved Raman Spectroscopy

Electron–phonon coupling in van der Waals (vdW) layered PdSe₂ is crucial for understanding and controlling emergent quantum phenomena such as anisotropic transport, symmetry breaking, and possible charge-density-wave (CDW) formation. Due to its low dimensionality and unique crystal structure, PdSe₂ exhibits strong, direction-dependent coupling that can be tuned by external factors such as magnetic field or strain.Here, we have prepared even-layered (8-layer) and odd-layered (5-layer) PdSe₂ samples and probed their electron–phonon coupling using helicity-resolved Raman spectroscopy at 2.3 K and 295 K, under external magnetic fields ranging from 0 to 9 T. The intensities of the A₁g, A₃g, and B₁g modes exhibit non-monotonic behavior with local maxima or minima, depending on the conserved/flipped (σ⁺⁺/σ⁺⁻) angular momentum response from the orbital–phonon interactions. In contrast, the A₂g, B₂g, and B₃g modes show no dependence on magnetic field from 0 to 9 T. Moreover, the critical magnetic field at which the σ⁺⁺ and σ⁺⁻ intensities cross varies between the even- and odd-layered PdSe₂ samples, suggesting that the underlying electron–orbital–phonon coupling mechanism goes beyond the semiclassical model and that quantum valley splitting should be considered. This work paves the way for understanding electron–phonon coupling in 2D magnetic systems through temperature- and magnetic-field-dependent optical probes.