Fig. 5: Comparison of CrBr₃ Raman spectra next to and under a FGT crystal.

To gain information about the influence of an FGT contact on the structure of the underlying CrBr₃ multilayer (magnetoconductance in Fig. 3), the Raman spectra of the CrBr₃ tunnel barrier next to and under the FGT electrode were compared. We focused on the two E_g modes near 140 cm⁻¹ and 150 cm⁻¹, known to be highly sensitive to the symmetry of the CrBr₃ structure. Raman spectra of CrBr₃ measured at different points of the CrBr₃ tunnel barrier, under crossed (XY, a) and parallel (XX, b) polarization configuration of the incident and detected light (data measured around 20 K). The red and blue curves are the Raman spectra measured at positions next to the FGT electrode (on opposite sides); the green curves are measured at different positions under the FGT electrode (see Supplementary Fig. 3 for position details). Under the FGT electrode, the peaks are broader and exhibit a shoulder (suggesting that they in fact consist of distinct peaks, i.e., that they are split). More importantly, the vertical dotted lines mark the peak position in CrBr₃ away from the FGT contact. It is apparent that under FGT the peak position is shifted. c, d Extracted peak wavelength of the two individual modes, as a function of position on the CrBr₃ multilayer where the measurements are done (on the x-axis, Distance = 0 μm corresponds to a position to the left of the FGT electrode; the FGT crystal is located at distances between approximately 3 μm and 5 μm). A polarization-dependent shift of the peaks measured under the FGT electrodes is apparent.