Pressure-Tuned Collapse of the Mott-Like State in Can+1RunO3n+1 (n=1,2): Raman Spectroscopic Studies

Abstract

We report a Raman scattering study of the pressure-induced collapse of the Mott-like phases of ${\mathrm{C}\mathrm{a}}_3{\mathrm{R}\mathrm{u}}_2{\mathrm{O}}_7$ ($T_N=56\mathrm{K}$) and ${\mathrm{C}\mathrm{a}}_2{\mathrm{R}\mathrm{u}\mathrm{O}}_4$ ($T_N=110\mathrm{K}$). The pressure dependence of the phonon and two-magnon excitations in these materials indicate (i) a $T\sim 0$ pressure-induced collapse of the antiferromagnetic (AF) insulating phase above $P^{*}\sim 55\mathrm{k}\mathrm{b}\mathrm{a}\mathrm{r}$ in ${\mathrm{C}\mathrm{a}}_3{\mathrm{R}\mathrm{u}}_2{\mathrm{O}}_7$ and $P^{*}\sim 5–10\mathrm{k}\mathrm{b}\mathrm{a}\mathrm{r}$ in ${\mathrm{C}\mathrm{a}}_2{\mathrm{R}\mathrm{u}\mathrm{O}}_4$, (ii) a remarkable insensitivity of the exchange interaction to pressure in both systems, and (iii) evidence for persistent AF correlations above the critical pressure of ${\mathrm{C}\mathrm{a}}_2{\mathrm{R}\mathrm{u}\mathrm{O}}_4$, suggestive of phase separation involving AF insulator and ferromagnetic metal phases.