Giant thermoelectric Seebeck coefficient of a two-dimensional electron gas in SrTiO3

Abstract

Enhancement of the Seebeck coefficient (S ) without reducing the electrical conductivity (σ) is essential to realize practical thermoelectric materials exhibiting a dimensionless figure of merit (ZT=S²·σ·T·κ⁻¹) exceeding 2, where T is the absolute temperature and κ is the thermal conductivity. Here, we demonstrate that a high-density two-dimensional electron gas (2DEG) confined within a unit cell layer thickness in SrTiO₃ yields unusually large |S|, approximately five times larger than that of SrTiO₃ bulks, while maintaining a high σ_2DEG. In the best case, we observe |S|=850 μV K⁻¹ and σ_2DEG=1.4×10³ S cm⁻¹. In addition, by using the κ of bulk single-crystal SrTiO₃ at room temperature, we estimate ZT ∼ 2.4 for the 2DEG, corresponding to ZT ∼ 0.24 for a complete device having the 2DEG as the active region. The present approach using a 2DEG provides a new route to realize practical thermoelectric materials without the use of toxic heavy elements.