title: Anisotropic Terahertz Emission from Bi2Se3 Thin Films with Inclined Crystal Planes.
abstract: We investigate the surface states of topological insulator (TI) Bi2Se3 thin films grown on Si nanocrystals and Al2O3 substrates by using terahertz (THz) emission spectroscopy. Compared to bulk crystalline Bi2Te2Se, film TIs exhibit distinct behaviors in the phase and amplitude of emitted THz radiation. In particular, Bi2Se3 grown on Al2O3 shows an anisotropic response with a strong modulation of the THz signal in its phase. From x-ray diffraction, we find that the crystal plane of the Bi2Se3 films is inclined with respect to the plane of the Al2O3 substrate by about 0.27°. This structural anisotropy affects the dynamics of photocarriers and hence leads to the observed anisotropic response in the THz emission. Such relevance demonstrates that THz emission spectroscopy can be a sensitive tool to investigate the fine details of the surface crystallography and electrostatics of thin film TIs.
authors.affiliation: Department of Physics and Photon Science, School of Physics and Chemistry, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju, 500-712, South Korea. syhamh@gist.ac.kr.
authors.forename: Sun Young
authors.initials: SY
authors.lastname: Hamh
authors.affiliation: Department of Physics and Photon Science, School of Physics and Chemistry, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju, 500-712, South Korea. parksh@gist.ac.kr.
authors.forename: Soon-Hee
authors.initials: SH
authors.lastname: Park
authors.affiliation: Department of Physics and Photon Science, School of Physics and Chemistry, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju, 500-712, South Korea. jwh@gist.ac.kr.
authors.forename: Jeongwoo
authors.initials: J
authors.lastname: Han
authors.affiliation: Department of Physics, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul, 136-701, South Korea. enaxn@korea.ac.kr.
authors.forename: Jeong Heum
authors.initials: JH
authors.lastname: Jeon
authors.affiliation: Department of Physics, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul, 136-701, South Korea. sjkahng@korea.ac.kr.
authors.forename: Se-Jong
authors.initials: SJ
authors.lastname: Kahng
authors.affiliation: Department of Applied Physics, College of Applied Science, Kyung Hee University, Yongin, 446-701, South Korea. sung@khu.ac.kr.
authors.forename: Sung
authors.initials: S
authors.lastname: Kim
authors.affiliation: Department of Applied Physics, College of Applied Science, Kyung Hee University, Yongin, 446-701, South Korea. sukho@khu.ac.kr.
authors.forename: Suk-Ho
authors.initials: SH
authors.lastname: Choi
authors.affiliation: Department of Electrical and Computer Engineering, Rutgers, The State University of New Jersey, 94 Brett Road, Piscataway, NJ, 08854, USA. bnamz@rutgers.edu.
authors.forename: Namrata
authors.initials: N
authors.lastname: Bansal
authors.affiliation: Department of Physics and Astronomy, Rutgers, The State University of New Jersey, 136 Frelinghuysen Road, Piscataway, NJ, 08854, USA. ohsean@physics.rutgers.edu.
authors.forename: Seongshik
authors.initials: S
authors.lastname: Oh
authors.affiliation: Department of Physics, Pohang University of Science and Technology, 77 Cheongam-Ro, Nam-Gu, Pohang, Gyeongbuk, 790-784, South Korea. june0521@postech.ac.kr.
authors.forename: Joonbum
authors.initials: J
authors.lastname: Park
authors.affiliation: Department of Physics, Pohang University of Science and Technology, 77 Cheongam-Ro, Nam-Gu, Pohang, Gyeongbuk, 790-784, South Korea. js.kim@postech.ac.kr.
authors.forename: Jun Sung
authors.initials: JS
authors.lastname: Kim
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA. kjmsy@gist.ac.kr.
authors.forename: Jae Myung
authors.initials: JM
authors.lastname: Kim
authors.affiliation: Department of Physics and Photon Science, School of Physics and Chemistry, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju, 500-712, South Korea. dynoh@gist.ac.kr.
authors.forename: Do Young
authors.initials: do Y
authors.lastname: Noh
authors.affiliation: Department of Physics and Photon Science, School of Physics and Chemistry, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju, 500-712, South Korea. jsl@gist.ac.kr.
authors.forename: Jong Seok
authors.initials: JS
authors.lastname: Lee
keywords: Bi2Se3; Terahertz emission; Thin film; Topological insulator