Signature of the Quantized Thermoelectric Hall Effect in a Topological Weyl Semimetal

Thermoelectrics are promising by directly generating electricity from waste heat. However, (sub-) room-temperature thermoelectrics has posed a long-standing challenge, due to the entropic nature of thermopower that is supressed at low temperature. In this light, topological materials offer a new avenue for energy harvest applications. Recent theories predicted that topological Weyl semimetals (WSMs) near quantum limit can lead to a non-saturating longitudinal thermopower, as well as a quantized thermoelectric Hall coefficient approaching to a universal value. Here, we experimentally demonstrate the non-saturating thermopower and the signature of quantized thermoelectric Hall coefficients in WSM tantalum phosphide (TaP). An ultrahigh longitudinal thermopower Sxx = 1.1x10^3 muV/K, along with a power factor ~300 muW/cm/K^2 , are observed ~50K. Moreover, the thermoelectric Hall coefficients develop a plateau at high-fields and low temperatures, which further collapse into a single curve determined by universal constants. Our work highlights the unique electronic structure and topological protection of Weyl nodes toward thermoelectric harvest applications at low temperature.