Quantum Oscillations in the High Pressure Metallic State of   Ca$_2$RuO$_4$
  We present evidence for quantum oscillations in the pressure-induced metallic state of the 4$d$ layered perovskite Ca$_2$RuO$_4$. A complicated oscillation spectrum is observed, which is both temperature and field dependent, with unusually light cyclotron masses in the range of $m^*/m_e$ $\sim$ 0.6 -- 3, suggesting that the pressure-induced metallic state is a weakly correlated Fermi liquid. We compare our observations to band structure calculations within the local spin density approximation, and conclude that some features of the spectrum are a result of non-linear spin splitting effects. 
Swee K. Goh, P. L. Alireza, Lina E. Klintberg, T. Murphy, F. Nakamura,   David J. Singh, Mike Sutherland
cond-mat.str-el