Dirac dispersion generates large Nernst effect in Weyl semimetals

TL;DR

This paper demonstrates that the Dirac dispersion in Weyl semimetals leads to an exceptionally large Nernst effect, providing a new experimental signature for topological states and the chiral anomaly.

Contribution

It introduces a theoretical and experimental analysis of the Nernst effect in Weyl semimetals, linking topology to thermoelectric responses with no adjustable parameters.

Findings

Nernst thermopower in NbP exceeds conventional thermopower by 100 times.

Pronounced maximum in Nernst effect near T_M=90 K.

Temperature and field dependence explained by Weyl fermion bipolarity.

Abstract

Weyl semimetals expand research on topologically protected transport by adding bulk Berry monopoles with linearly dispersing electronic states and topologically robust, gapless surface Fermi arcs terminating on bulk node projections. Here, we show how the Nernst effect, combining entropy with charge transport, gives a unique signature for the presence of Dirac bands. The Nernst thermopower of NbP (maximum of 800 microV K-1 at 9 T, 109 K) exceeds its conventional thermopower by a hundredfold and is significantly larger than the thermopower of traditional thermoelectric materials. The Nernst effect has a pronounced maximum near T_M=90 +/- 20 K=mu_0/kB (mu_0 is chemical potential at T=0 K). A self-consistent theory without adjustable parameters shows that this results from electrochemical potential pinning to the Weyl point energy at T>=TM, driven by charge neutrality and Dirac band symmetry. Temperature and field dependences of the Nernst effect, an even function of the charge polarity, result from the intrinsically bipolar nature of the Weyl fermions. Through this study, we offer an understanding of the temperature dependence of the position of the electrochemical potential vis-a-vis the Weyl point, and we show a direct connection between topology and the Nernst effect, a potentially robust experimental tool for investigating topological states and the chiral anomaly.