Open AccessBreaking of Thermopower–Conductivity Trade‐Off in LaTiO 3 Film around Mott Insulator to Metal Transition
Author(s) -
Katase Takayoshi,
He Xinyi,
Tadano Terumasa,
Tomczak Jan M.,
Onozato Takaki,
Ide Keisuke,
Feng Bin,
Tohei Tetsuya,
Hiramatsu Hidenori,
Ohta Hiromichi,
Ikuhara Yuichi,
Hosono Hideo,
Kamiya Toshio
Publication year - 2021
Publication title -
advanced science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.388
H-Index - 100
ISSN - 2198-3844
DOI - 10.1002/advs.202102097
Subject(s) - seebeck coefficient , condensed matter physics , materials science , epitaxy , mott insulator , thermoelectric effect , conductivity , metal , transition metal , metal–insulator transition , lattice (music) , electrical resistivity and conductivity , mott transition , nanotechnology , thermal conductivity , superconductivity , composite material , chemistry , physics , thermodynamics , metallurgy , catalysis , quantum mechanics , hubbard model , biochemistry , layer (electronics) , acoustics
Introducing artificial strain in epitaxial thin films is an effective strategy to alter electronic structures of transition metal oxides (TMOs) and to induce novel phenomena and functionalities not realized in bulk crystals. This study reports a breaking of the conventional trade‐off relation in thermopower ( S )–conductivity ( σ ) and demonstrates a 2 orders of magnitude enhancement of power factor (PF) in compressively strained LaTiO 3 (LTO) films. By varying substrates and reducing film thickness down to 4 nm, the out‐of‐plane to the in‐plane lattice parameter ratio is controlled from 0.992 (tensile strain) to 1.034 (compressive strain). This tuning induces the electronic structure change from a Mott insulator to a metal and leads to a 10 3 ‐fold increase in σ up to 2920 S cm −1 . Concomitantly, the sign of S inverts from positive to negative, and both σ and S increase and break the trade‐off relation between them in the n‐type region. As a result, the PF (= S 2 σ ) is significantly enhanced to 300 µW m − 1 K −2 , which is 10 2 times larger than that of bulk LTO. Present results propose epitaxial strain as a means to finely tune strongly correlated TMOs close to their Mott transition, and thus to harness the hidden large thermoelectric PF.