TY - JOUR
T1 - Thermoelectric properties of 3D topological insulator
T2 - Direct observation of topological surface and its gap opened states
AU - Matsushita, Stephane Yu
AU - Huynh, Khuong Kim
AU - Yoshino, Harukazu
AU - Tu, Ngoc Han
AU - Tanabe, Yoichi
AU - Tanigaki, Katsumi
N1 - Funding Information:
This work was supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), JSPS KAKENHI Grants No. JP15K05148, No. JP17K14074, and No. 17869341. This work was sponsored by research grants from Murata Science Foundation and Yazaki Memorial Foundation. This work was partly performed at High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University (Project No. 15H0204). S.Y.M. thanks Tohoku University Interdepartmental Doctoral Degree Program for Multi-dimensional Materials Science Leaders for financial support.
Publisher Copyright:
© 2017 American Physical Society.
PY - 2017/10/13
Y1 - 2017/10/13
N2 - We report thermoelectric (TE) properties of topological surface Dirac states (TSDS) in three-dimensional topological insulators (3D-TIs) purely isolated from the bulk by employing single-crystal Bi2-xSbxTe3-ySey films epitaxially grown in the ultrathin limit. Two intrinsic nontrivial topological surface states, a metallic TSDS (m-TSDS) and a gap-opened semiconducting topological state (g-TSDS), are successfully observed by electrical transport, and important TE parameters [electrical conductivity (σ), thermal conductivity (κ), and thermopower (S)] are accurately determined. Pure m-TSDS gives S=-44μVK-1, which is an order of magnitude higher than those of the conventional metals and the value is enhanced to -212μVK-1 for g-TSDS. It is clearly shown that the semiclassical Boltzmann transport equation (SBTE) in the framework of constant relaxation time (τ) most frequently used for conventional analysis cannot be valid in 3D-TIs and strong energy dependent relaxation time τ(E) beyond the Born approximation is essential for making intrinsic interpretations. Although σ is protected on the m-TSDS, κ is greatly influenced by the disorder on the topological surface, giving a dissimilar effect between topologically protected electronic conduction and phonon transport.
AB - We report thermoelectric (TE) properties of topological surface Dirac states (TSDS) in three-dimensional topological insulators (3D-TIs) purely isolated from the bulk by employing single-crystal Bi2-xSbxTe3-ySey films epitaxially grown in the ultrathin limit. Two intrinsic nontrivial topological surface states, a metallic TSDS (m-TSDS) and a gap-opened semiconducting topological state (g-TSDS), are successfully observed by electrical transport, and important TE parameters [electrical conductivity (σ), thermal conductivity (κ), and thermopower (S)] are accurately determined. Pure m-TSDS gives S=-44μVK-1, which is an order of magnitude higher than those of the conventional metals and the value is enhanced to -212μVK-1 for g-TSDS. It is clearly shown that the semiclassical Boltzmann transport equation (SBTE) in the framework of constant relaxation time (τ) most frequently used for conventional analysis cannot be valid in 3D-TIs and strong energy dependent relaxation time τ(E) beyond the Born approximation is essential for making intrinsic interpretations. Although σ is protected on the m-TSDS, κ is greatly influenced by the disorder on the topological surface, giving a dissimilar effect between topologically protected electronic conduction and phonon transport.
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U2 - 10.1103/PhysRevMaterials.1.054202
DO - 10.1103/PhysRevMaterials.1.054202
M3 - Article
AN - SCOPUS:85046530278
VL - 1
JO - Physical Review Materials
JF - Physical Review Materials
SN - 2475-9953
IS - 5
M1 - 054202
ER -