Origin of anomalous temperature dependence of the Nernst effect in narrow-gap semiconductors

Prototypical many-body signatures in transport properties of semiconductors

“…In fact, this is expected, as FeSb 2 violates the upper bound, |S| ≤ ∆/T , for a thermopower exclusively driven by electron diffusion [10]. As alluded to in the introduction, this riddle was successfully solved [10][11][12][13][14][15] by attributing the colossal amplitude to the phonon-drag effect. Simply speaking, the thermal gradient also leads to a nonequilibrium phonon distribution.…”

“…Agreement with experiment confirms that our approximations for the kernels-linearized self-energy, omission of vertex corrections-conserves the essential physics. Instead, in previous modelings of FeSb 2 , based on semi-classical approaches [13][14][15], resistivities and the Hall coefficient either diverged at low T or had to be suppressed by impurity states, e.g., by forcing the chemical potential into the conduction band. An alternative scenario for residual conduction in FeSb 2 could be provided by the recent observation of metallic surface states [9,113].…”

“…1). Alternatively, the temperature dependence of the chemical potential can be engineered by assuming in-gap impurity states [13][14][15]. Given that transport observables exhibit three to four distinct regimes, phenomenological modellings actually used up to three impurity levels to properly guide the chemical potential [13].…”

“…Here, we focus on the presence of characteristic temperatures that mark features across various transport quantities [8]: For instance, at low temperatures, inflection points in the resistivity ρ and the Seebeck coefficient S correlate with maxima in the Hall and Nernst coefficient, R H , ν. This intriguingbut by no means uncommon [1,17,18]-temperature profile, has previously been advocated to derive from extrinsic in-gap states [13][14][15][19][20][21]. Prototypical transport in semiconductors.…”

“…1 for a simple two-band modeling of the colossal thermopower material FeSb 2 [6][7][8][9]. The large magnitude of its S and ν originates from the phonon-drag effect [10][11][12][13][14][15] [16]. Here, we focus on the presence of characteristic temperatures that mark features across various transport quantities [8]: For instance, at low temperatures, inflection points in the resistivity ρ and the Seebeck coefficient S correlate with maxima in the Hall and Nernst coefficient, R H , ν.…”