Heat capacity study of magneto-electronic phase separation in La1-xSrxCoO3 single crystals.*

We present an investigation of the specific heat (0.35 K $< \quad T \quad <$ 270 K) and ordinary Hall effect (300 K) in La$_{1-x}$Sr$_{x}$CoO$_{3}$ single crystals (0.00 $< \quad x \quad <$ 0.30). The data reveal new information on the nature of the percolation transition, the crystal and electronic structure, and the magneto-electronic phase separation. The observations include a discontinuity in Debye temperature accompanying the percolation-type insulator-metal transition and a large electron mass enhancement, likely due to strong electron correlation effects. The various contributions to the heat capacity provide a detailed picture of the evolution of the phase-separated state with doping. Most importantly, this provides strong evidence for the unanticipated result that the phase separation is restricted to a well-defined doping range, 0.04 $< \quad x \quad <$ 0.22, in close agreement with recent small-angle neutron scattering.