Evidence of spin-phonon coupling in ${\mathrm{CrSiTe}}_3$

We present Raman scattering results on the layered semiconducting ferromagnetic compound ${\mathrm{CrSiTe}}_3$. Four Raman-active modes, predicted by symmetry, are observed and assigned. The experimental results are supported by density functional theory calculations. The self-energies of the $A_g^3$ and the $E_g^3$ symmetry modes exhibit unconventional temperature evolution around 180 K. In addition, the doubly degenerate $E_g^3$ mode shows a clear change of asymmetry in the same temperature region. The observed behavior is consistent with the presence of the previously reported short-range magnetic order and strong spin-phonon coupling.

Figure 1

Raman spectra of ${\mathrm{CrSiTe}}_3$ single crystals measured at 100 K in (a) parallel and (b) cross polarization configurations. The gray line represents the ${\mathrm{TeO}}_2$ spectrum measured at 300 K. Inset: Raman spectrum of ${\mathrm{CrGeTe}}_3$ in the parallel polarization configuration measured at 100 K.

Figure 2

(a) The $E_g^3$ mode Raman spectra of ${\mathrm{CrSiTe}}_3$ at four temperatures measured in the cross polarization configuration. Blue lines represent line shapes obtained as a convolution of the Fano line shape and Gaussian, calculated to fit the experimetal data. Temperature dependence of (b) the energy, (c) the line width, and (d) the Fano parameter $q$ of the $E_g^3$ mode. The dashed red line represents standard anharmonic behavior [28, 29]. All the parameters show a change in tendency around 180 K.

Figure 3

(a) $A_g^3$ mode Raman spectra of ${\mathrm{CrSiTe}}_3$ at four temperatures measured in the parallel polarization configuration. Blue lines represent Voigt line shapes. (b) Energy and (c) line-width temperature dependence of the $A_g^3$ mode.

Figure 4

Unit cell of a ${\mathrm{CrSiTe}}_3$ single crystal (solid lines) with the displacement patterns of the $A_g$ and $E_g$ symmetry modes. Arrow lengths are proportional to the square root of the interatomic forces.

Figure 5

Analysis of the $E_g^3$ asymmetry. Measured data are shown as the black line. The solid blue line represents the line shape obtained as a convolution of the Fano line shape and a Gaussian, whereas the orange line represents a Voigt line shape, both calculated to fit the experimental data. The Voigt profile deviates from the experimental data at the peak flanks.

Figure 6

The $E_g^3$ mode Raman spectra of ${\mathrm{CrSiTe}}_3$ at all temperatures measured in the cross polarization configuration. Blue lines represent calculated spectra obtained as the convolution of the Fano line shape and Gaussian.