Multiband transport hierarchy and large Nernst effect in EuAuBi: Establishing a Nernst scaling for asymmetric multiband systems

Abstract

In correlated materials, coexisting pockets of vastly different carrier densities raise two fundamental questions: which pocket governs the various transport coefficients, and does the conventional Nernst scaling $\hat{I}½/T\propto \hat{I}¼/E_F$, originally derived for single-band systems, still hold? We address both questions in the polar semimetal EuAuBi, where a dilute electron pocket ($n_e\sim 10^{16}{\mathrm{cm}}^{-3}$) coexists with a dense hole pocket ($n_h\sim 10^{21}{\mathrm{cm}}^{-3}$). We find a clear hierarchy: the hole pocket dominates the longitudinal resistivity; the Hall effect crosses from electron- to hole-dominance with increasing field; the Seebeck coefficient is dominated by the electron pocket at low temperature and by both pockets at high temperature. Remarkably, the Nernst effect is governed entirely by the ultrahigh-mobility electron pocket, yielding a large low-field signal of $\sim 5\hat{I}¼V/K$ near 1~T at 202~K, comparable to anomalous Nernst signals in magnetic Weyl semimetals. By analyzing the two-band thermoelectric conductivity, we show that the Nernst coefficient follows a scaling $\hat{I}½/T\propto \hat{I}{¼}_e/E_{F,tot}$. This scaling originates from a compensation between the electron-to-hole conductivity ratio and the Fermi-energy ratio, establishing that the large Nernst effect is a semiclassical multiband phenomenon rather than a topological Berry-curvature contribution. This understanding advances the thermoelectric transport physics of multiband electronic systems and offers a guiding principle for low-field transverse thermoelectric design.

6 pages,3 figures