title: Terahertz single conductance quantum and topological phase transitions in topological insulator Bi₂Se₃ ultrathin films.
abstract: Strong spin-orbit interaction and time-reversal symmetry in topological insulators generate novel quantum states called topological surface states. Their study provides unique opportunities to explore exotic phenomena such as spin Hall effects and topological phase transitions, relevant to the development of quantum devices for spintronics and quantum computation. Although ultrahigh-vacuum surface probes can identify individual topological surface states, standard electrical and optical experiments have so far been hampered by the interference of bulk and quantum well states. Here, with terahertz time-domain spectroscopy of ultrathin Bi₂Se₃ films, we give evidence for topological phase transitions, a single conductance quantum per topological surface state, and a quantized terahertz absorbance of 2.9% (four times the fine structure constant). Our experiment demonstrates the feasibility to isolate, detect and manipulate topological surface states in the ambient at room temperature for future fundamental research on the novel physics of topological insulators and their practical applications.
authors.affiliation: Department of Physics, Yonsei University, Seoul 120-749, Republic of Korea.
authors.forename: Byung Cheol
authors.initials: BC
authors.lastname: Park
authors.affiliation: Department of Physics, Yonsei University, Seoul 120-749, Republic of Korea.
authors.forename: Tae-Hyeon
authors.initials: TH
authors.lastname: Kim
authors.affiliation: Department of Physics, Yonsei University, Seoul 120-749, Republic of Korea.
authors.forename: Kyung Ik
authors.initials: KI
authors.lastname: Sim
authors.affiliation: School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 500-712, Republic of Korea.
authors.forename: Boyoun
authors.identifier: 0000000336503614
authors.initials: B
authors.lastname: Kang
authors.affiliation: Division of Industrial Metrology, Korea Research Institute of Standards and Science (KRISS), Daejeon 305-340, Republic of Korea.
authors.forename: Jeong Won
authors.initials: JW
authors.lastname: Kim
authors.affiliation: School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 500-712, Republic of Korea.
authors.forename: Beongki
authors.initials: B
authors.lastname: Cho
authors.affiliation: Department of Physics, Yonsei University, Seoul 120-749, Republic of Korea.
authors.forename: Kwang-Ho
authors.initials: KH
authors.lastname: Jeong
authors.affiliation: Department of Physics, Yonsei University, Seoul 120-749, Republic of Korea.
authors.forename: Mann-Ho
authors.initials: MH
authors.lastname: Cho
authors.affiliation: Department of Physics, Yonsei University, Seoul 120-749, Republic of Korea.
authors.forename: Jae Hoon
authors.initials: JH
authors.lastname: Kim