Robust narrow-gap semiconducting behavior in square-net La$_{3}$Cd$_{2}$As$_{6}$

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 and characterization of a new family of narrow-gap semiconductors, R3Cd2As6 (R = La, Ce). Single crystal x-ray diffraction at room temperature reveals that the As square nets distort and Cd vacancies order in a monoclinic superstructure. A putative charge-density ordered state sets in at 279 K in La3Cd2As6 and at 136 K in Ce3Cd2As6 and is accompanied by a substantial increase in the electrical resistivity in both compounds. The resistivity of the La member increases by thirteen orders of magnitude on cooling, which points to a remarkably clean semiconducting ground state. Our results suggest that light square net materials within a I4/mmm parent structure are promising clean narrow-gap semiconductors.