Observation of a Structurally-Driven Mott Transition in Single Crystal Ca 2RuO 4

T=357 K in single crystal Ca 2RuO 4, an isomorph to the superconductor Sr 2RuO 4. A discontinuous jump in electrical resistivity with a concomitant change in magnetic moment is triggered by a pronounced structural transition from a high temperature tetragonal phase to a low temperature orthorhombic phase. We argue that the elastic energy associated with the reduction of the crystal symmetry coupled with the electronic delocalization energy represent primary forces that drive the observed Mott transition. PACS: 61.10 Nz, 71.30 +h, 75.30-m. The d-shell of the 4d and 5d-transition metal cations in transition metal oxides (TMO) are more extended than their more thoroughly studied 3d counterparts. On the one hand this suggests a robust electron-phonon interaction between the d-electrons and the lattice which in the extreme could lead to structural phase transitions. Transitions to lower symmetry with decreasin