Axis-Dependent Conduction Polarity in WSi2 Single Crystals

Abstract

Materials that demonstrate axis-dependent conduction polarity enable new technologies by integrating p- and n-type functionality into a single crystal. Certain anisotropic crystal structures give rise to this behavior by having dominant electron conduction along one crystallographic direction and dominant hole conduction along another. However, only a few materials have been experimentally shown to demonstrate this unique property. Here, we identify axis-dependent conduction polarity in tetragonal α-WSi2: a durable, thermally robust, and oxidation-resistant metal synthesized from earth-abundant elements. Two single crystals of α-WSi2 were prepared using Xe floating zone techniques, and their anisotropic conduction properties were evaluated. Simultaneous positive and negative thermopowers measured along the [100] and [001] directions, respectively, indicate that this material exhibits axis-dependent conduction polarity, which closely matches theoretical predictions. Hall measurements also show dominant p-type and n-type conduction along these respective crystallographic directions. Heat capacity measurements indicate that the density of states of these crystals is close to that of an exact α-WSi2 stoichiometry, confirming that this polarity anisotropy exists in relatively undoped crystals. In total, α-WSi2 is an excellent material platform for the future exploration of potential applications of this phenomenon.