Cryogenic Thermoelectric Enhancement by Nonparabolic Band-Edge Transport in Bi₂Te₃

Selective scattering of electrons near the Fermi level is the kinetic origin of the thermoelectric effect. Pronounced band nonparabolicity near the band edge is expected to promote the decoupling of a high Seebeck coefficient from high electrical conductivity; however, accessing this band-edge transport regime at low temperatures remains challenging, as defect-dominated scattering often masks the intrinsic band-structure effects. Here, we experimentally show that single-crystalline Bi₂Te₃ can access a reduced-scattering band-edge transport regime in which the transport distribution becomes strongly energy dependent, enabling simultaneously a sizable thermopower and a high carrier mobility at cryogenic temperatures. This approach yields a record thermoelectric power factor of three times as high as that of conventional parabolic band-dominated Bi₂Te₃. Quantum oscillation measurements reveal multiband transport components consistent with the band-structure complexity of Bi₂Te₃, and magneto-thermal conductivity measurements indicate a reduced Lorenz factor and suppressed electronic thermal conductivity in the same regime. The resultant over 600% thermoelectric enhancement in conventional Bi₂Te₃ demonstrates a practical strategy of advancement by engineering band-edge transport in strong spin-orbit coupled materials.