Electronic Fine Structure in the Electron-Hole Plasma in SrB6

Abstract

Electron-hole mixing-induced fine structure in alkaline earth hexaborides leads to lower energy (temperature) scales, and thus a stronger tendency toward an excitonic instability than in their doped counterparts (viz. Ca 1 − x La x B 6 , x ≈ 0.005 \) , which are high-Curie-temperature, small-moment ferromagnets. Comparison of Fermi surfaces and spectral distributions with de Haas–van Alphen, optical, transport, and tunneling data indicates that SrB 6 remains a fermionic semimetal down to (at least) 5 K, rather than forming an excitonic condensate. For the doped system the Curie temperature is higher than the degeneracy temperature.