Thermoelectricity in correlated narrow-gap semiconductors

Abstract

We review many-body effects, their microscopic origin, as well as their impact on thermoelectricity in correlated narrow-gap semiconductors. Members of this class-such as FeSi and FeSb-display an unusual temperature dependence in various observables: insulating with large thermopowers at low temperatures, they turn bad metals at temperatures much smaller than the size of their gaps. This insulator-to-metal crossover is accompanied by spectral weight-transfers over large energies in the optical conductivity and by a gradual transition from activated to Curie-Weiss-like behaviour in the magnetic susceptibility. We show a retrospective of the understanding of these phenomena, discuss the relation to heavy-fermion Kondo insulators-such as CeBiPt for which we present new results-and propose a general classification of paramagnetic insulators. From the latter, FeSi emerges as an orbital-selective Kondo insulator. Focussing on intermetallics such as silicides, antimonides, skutterudites, and Heusler compounds we showcase successes and challenges for the realistic simulation of transport properties in the presence of electronic correlations. Further, we explore new avenues in which electronic correlations may contribute to the improvement of thermoelectric performance.

First-principles calculations of charge carrier mobility and conductivity in bulk semiconductors and two-dimensional materials

“…The external Hamiltonian given in Eq. (73) can be obtained by applying the minimal coupling substitutionp →p − (−e)A(z) to the equilibrium HamiltonianĤ eq =Ĥ 0 +Ĥ int . We note that in Eq.…”

Putative hybridization gap in CaMn2Bi2 under applied pressure

“…If the small transport gap in CaMn 2 Bi 2 were due to band structure of uncorrelated electrons, pressure thus should promote a metallic state [19]. However, if CaMn 2 Bi 2 is indeed a hybridization gap semiconductor, the band gap could increase as a function of pressure as the hybridization between Mn 3d and conduction electrons increases, akin to Ce 3 Bi 4 Pt 3 and FeSi under pressure [20][21][22]. In contrast, if the Mn 3d ions become more localized with increasing pressure, the hybridization gap can decrease as a function of pressure similar to SmB 6 under pressure [23].…”

Isoelectronic tuning of heavy fermion systems: Proposal to synthesize Ce3Sb4Pd3

“…Indeed, as has been demonstrated in Ref. 4 it is the hybridization of the Ce-4f orbitals to their surrounding that accounts for the gap opening: Treating the Ce-f (J=5/2) as core-states results in metallic ground-states, in analogy to a periodic Anderson model with vanishing hybridization between localized f and conduction states.…”