Optical Conductivity of High Entropy Alloys Based on BaMnSb₂

Recent work has shown that the Dirac (linear) band dispersion and spin valley electronic states can be engineered through high-entropy alloying of Dirac semimetals, such as BaMnSb₂ (Laha, A., Yoshida, S., Marques dos Santos Vieira, F. et al. Nat Commun 15, 3532 (2024)). Optical conductivity provides a reliable tool for probing electronic band structure and in this work, we demonstrate the existence of linear band dispersion in high entropy compounds of BaMnSb₂ alloyed with Ca, Eu and/or Yb. We measured broadband reflectance between 100 cm^-1 and 50,000 cm^-1 (12 meV to 6 eV), at temperatures from 300 K to 80K, for different high entropy crystals. Similar to the pure BaMnSb₂, optical conductivity (σ₁(ω)) determined from Kramers-Kronig transformation of reflectance in the alloyed, i.e. high entropy systems, show large regions of linear frequency dependence, characteristic to interband transitions involving Dirac (linear) electronic branches. The absorption spectrum is in good qualitative agreement with previous band structure calculations. Moreover, we show that the temperature dependence of the plasma edge and the loss function peak are also very similar between the pure compound and the heavily alloyed phase.