Pressure-Tuned Collapse of the Mott-Like State in Ca_{n+1}Ru_nO_{3n+1} (n=1,2): Raman Spectroscopic Studies

TL;DR

This study uses Raman spectroscopy to investigate how pressure causes the collapse of Mott-like insulating phases in Ca_3Ru_2O_7 and Ca_2RuO_4, revealing critical pressures and phase separation phenomena.

Contribution

It provides new insights into pressure-induced phase transitions and magnetic correlations in Ca_{n+1}Ru_nO_{3n+1} compounds, highlighting the role of Ru-O distortions.

Findings

Collapse of antiferromagnetic insulating phase above critical pressures

Persistent antiferromagnetic correlations beyond phase transition

Evidence of phase separation into AF insulator and ferromagnetic metal

Abstract

We report a Raman scattering study of the pressure-induced collapse of the Mott-like phases of Ca_3Ru_2O_7 (T_N=56 K) and Ca_2RuO_4 (T_N=110 K). The pressure-dependence of the phonon and two-magnon excitations in these materials indicate: (i) a pressure-induced collapse of the antiferromagnetic (AF) insulating phase above P* ~ 55 kbar in Ca_3Ru_2O_7 and P* ~ 5-10 kbar in Ca_2RuO_4, reflecting the importance of Ru-O octahedral distortions in stabilizing the AF insulating phase; and (ii) evidence for persistent AF correlations above the critical pressure of Ca_2RuO_4, suggestive of phase separation involving AF insulator and ferromagnetic metal phases.