Raman scattering studies of spin, charge, and lattice dynamics in ${\mathrm{Ca}}_{2-x}{\mathrm{Sr}}_x{\mathrm{RuO}}_4$ $(0\mathrm{}<~x<\mathrm{}0.2)$

We use Raman scattering to study spin, charge, and lattice dynamics in various phases of ${\mathrm{Ca}}_{2-x}{\mathrm{Sr}}_x{\mathrm{RuO}}_4.$ With increasing substitution of Ca by Sr in the range $0<~x<\mathrm{}0.2,$ we observe (1) evidence for an increase of the electron-phonon interaction strength, (2) an increased temperature dependence of the two-magnon energy and linewidth in the antiferromagnetic insulating phase, and (3) evidence for charge gap development significantly below the metal-insulator transition ${(T}_{\mathrm{MI}}),$ and hysteresis associated with the structural phase change, both of which are indicative of a first-order metal-insulator transition and a coexistence of metallic and insulating components for $T<\mathrm{}{T}_{\mathrm{MI}}.$