Broken weak and strong spin rotational symmetries and tunable interaction between phonon and the continuum in Cr2Ge2Te6

Abstract: Phase transitions with lowering temperature is a manifestation of decreased entropy and within the Landau theoretical framework these are accompanied by the symmetry breaking. Whenever a symmetry is broken weakly or strongly, it leaves its trail and the same may be captured indirectly using renormalization of the quasi-particle excitations. Cr2Ge2Te6, a quasi-two-dimensional magnetic material, provides a rich playground to probe dynamics of the quasi-particle excitations as well as multiple phase transitions with lowering temperature intimately linked with the lattice and spin degrees of freedom. Here, we report in-depth inelastic light scattering measurements on single crystals of Cr2Ge2Te6 as a function of temperature, from 6 K to 330 K, and polarization. Our measurements reveal the long as well as short range ordering of the spins below Tc (~ 60 K) and T* (~ 180 K), respectively; setting the stage for broken rotational and time reversal symmetry, gauged via the distinct renormalization of the phonon self-energy parameters along with the modes intensity. Our measurements also uncovered an intriguing dependence of the interaction strength between discrete state (phonon here) and the underlying continuum, quantified using the Fano asymmetry parameter, as a function of the scattered light polarization. Our results suggest the possibility of tuning the interaction strength using controlled scattered light and symmetry in this 2D magnet.