Electronic Transport Properties and Band Structure of 2-D Material NaSn$_{2}$As$_{2}$

2-D-like materials potentially have superior thermoelectric properties compared to traditional 3-D materials when the conduction mechanisms are different in the plane and along the c-axis. A classic example is that of n-type tetradymites, where the difference between electron and phonon anisotropies is exploited. Here we explore a material in which the polarity of the Hall and Seebeck signals are different. We present electrical and thermoelectric transport properties of NaSn$_{2}$As$_{2}$, a quasi-2-D system, with Na atom embedded between nearly-2D Sn-As layers. It shows typical metallic behavior with its resistance increasing linearly with temperature. Its Hall measurement shows a p-type behavior, with anomalous slope change with applied magnetic field, which varies over temperature. At the same time, its Seebeck coefficient is measured to be negative, increasing with temperature. DFT band structure calculations, confirmed ARPES measurements$^{1}$,show that this material is a 2-carrier system, which explains the discrepancy between Hall and Seebeck data. We conclude that the conduction mechanisms should be different in-plane and along the c-axis. 1. M. Arguilla, et al. ACS Nano 2016, 10, 9500−9508