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Nature Materials 6, 129–134 (1 February 2007) | doi:10.1038/nmat1821

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

Hiromichi Ohta , SungWng Kim , Yoriko Mune , Teruyasu Mizoguchi , Kenji Nomura , Shingo Ohta , Takashi Nomura , Yuki Nakanishi , Yuichi Ikuhara , Masahiro Hirano , Hideo Hosono & Kunihito Koumoto

Enhancement of the Seebeck coefficient (S|[thinsp]|) without reducing the electrical conductivity (|[sigma]|) is essential to realize practical thermoelectric materials exhibiting a dimensionless figure of merit (ZT=S2|[middot]||[sigma]||[middot]|T|[middot]|κ|[minus]|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 |[sigma]|2DEG. In the best case, we observe |S|=850|[thinsp]||[mu]|V|[thinsp]|K|[minus]|1 and |[sigma]|2DEG=1.4|[times]|103|[thinsp]|S|[thinsp]|cm|[minus]|1. In addition, by using the κ of bulk single-crystal SrTiO3 at room temperature, we estimate ZT|[sim]|2.4 for the 2DEG, corresponding to ZT|[sim]|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.