An Anomalous Magneto-Optic Effect in Epitaxial Indium Selenide Layers

Abstract

Single-phonon modes offer potential applications in quantum phonon optics, but the phonon density of states of most materials consist of mixed contributions from coupled phonons. Here, using theoretical calculations and magneto-Raman measurements, we report two single-phonon vibration modes originating from the breathing and opposite out-of-plane vibrations of InSe layers. These single-phonon vibrations exhibit an anticorrelated scattering rotations of the polarization axis under an applied vertical magnetic field; such an anomalous magneto-optical behavior is due to the reverse bond polarizations of two quantum atomic vibrations, which induce different symmetry for the corresponding Raman selection rules. A 180° (+90° and −90°) integrated scattering rotation angle of two single-phonon modes was achieved when the magnetic field was swept from 0 to 6 T. This work demonstrates new ways to manipulate the magneto-optic effect through phonon polarity-based symmetry control and opens avenues for exploring single-phonon-vibration-based nanomechanical oscillators and magneto-phonon-coupled physics.

Strain-Induced Bandgap Enhancement of InSe Ultrathin Films with Self-Formed Two-Dimensional Electron Gas

“…Raman spectroscopy is further performed to measure the phonon vibration modes of epitaxially grown InSe films, as shown in Figure f. By comparing to the bulk InSe and In 2 Se 3 crystals, we identify three vibrational modes of MBE-grown InSe films as 112 cm –1 , 174 cm –1 , and 227 cm –1 , consistent with previous studies of A 1 g 1 , E 2 g 1 , and A 1 g 2 , respectively. ,, The single-phonon vibrations of A 1 g 1 and A 1 g 2 originate from the breathing and opposite out-of-plane vibrations of In–Se layers, respectively, and can induce an anomalous magneto-optic effect revealed by recent magneto-Raman measurements . Such spectrum characteristics are highly distinguished between InSe and In 2 Se 3 samples, as indicated by the signals of vertical broken cyan lines.…”

“…9,13,14 The single-phonon vibrations of A 1g 1 and A 1g 2 originate from the breathing and opposite out-of-plane vibrations of In−Se layers, respectively, and can induce an anomalous magneto-optic effect revealed by recent magneto-Raman measurements. 30 Such spectrum characteristics are highly distinguished between InSe and In 2 Se 3 samples, as indicated by the signals of vertical broken cyan lines. Combining with the STM observations of atomic structure, we thus unambiguously confirm the epitaxial growth of InSe films with controlled thickness.…”

“…We cannot exclude contributions from other mechanisms, such as the exciton characters due to the Coulomb interaction, 17 or certain vibrational phonon modes by the electron−phonon coupling. 30 Nevertheless, the exact origin of these midgap states still remains unsolved deserving further investigations, and probably extends additional degree of freedom to tune the exotic electronic properties of 2D InSe. To gain deeper insight into the band gap nature of InSe films, we investigate the variation of the electronic structure under various crystalline perturbations.…”

Chiral Phonons and Giant Magneto‐Optical Effect in CrBr3 2D Magnet

“…It is known that an external magnetic field breaks the time‐reversal symmetry in non‐magnetic materials, [ 9,10 ] leading to magneto‐optical Faraday and Kerr rotation effects. [ 11,12 ] Giant magneto‐optical Raman effects have also been observed in non‐magnetic InSe [ 13 ] and MoS 2 . [ 14 ] These effects arise from the magnetic‐field‐induced Lorentz force on the electrons, which results in a large magnetic‐field dependence of the Raman intensity for out‐of‐plane vibrational modes.…”

Observation of nonreciprocal magnetophonon effect in nonencapsulated few-layered CrI 3

“…The nonreciprocal magneto-optical scattering effect is observed in ferromagnetic few-layer CrI 3 , which probably uncovers a new nonreciprocal magneto-optical effect, besides Faraday effect, Kerr effect, and magnetic circular dichroism. Our observation may stimulate both experimental and theoretical investigations of magnetooptical scattering effect (42).…”