Weyl Semimetal TaAs: Crystal Growth, Morphology, and Thermodynamics

Abstract

Tantalum arsenide is experimentally verified as a Weyl semimetal recently. However, it is difficult to grow large TaAs single crystals due to the decomposition prior to reaching its melting point. Here we report an improved chemical vapor transport method using iodine as an agent to get large-size, high-quality TaAs single crystals up to 1 cm. X-ray diffraction confirmed that they are tetragonal TaAs. Specific heat of TaAs was measured from 2 K to room temperature, and hence the entropy and enthalpy were obtained, which are helpful in designing the optimal growth conditions. The as-grown crystals exhibit polyhedral morphology consisting of {101}, {001}, {103}, and {112} facets. The key points in crystal growth include using tantalum in the form of foils instead of powder as the starting material, tilting ampule to enhance convections and controlling the concentration of agent iodine. These measures should be applicable to the growth of other transition metal arsenides and phosphides.