Robust Narrow-Gap Semiconducting Behavior in Square-Net La₃Cd₂As₆

ABSTRACT: Narrow-gap semiconductors are sought-after materials due to their potential for long-wavelength detectors, thermoelectrics, and more recently non-trivial topology. Here we report the synthesis characterization of a new family narrow-gap semiconductors, $R$$_{3}$Cd$_{2}$As$_{6}$ ($R=$ La, Ce). Single crystal x-ray diffraction at room temperature reveals that As square nets distort Cd vacancies order in monoclinic superstructure. A putative charge-density ordered state sets 279~K La$_{3}$Cd$_{2}$As$_{6}$ 136~K Ce$_{3}$Cd$_{2}$As$_{6}$ is accompanied by substantial increase electrical resistivity both compounds. The La member increases thirteen orders magnitude on cooling, which points remarkably clean semiconducting ground state. Our results suggest light net within $I4/mmm$ parent structure promising semiconductors.