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. Ca₁₋ₓ LaₓB₆, 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 SrB₆ 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.