THz-ARPES band structure movies of Dirac surface currents
e-mail: danwakai@issp.u-tokyo.ac.jp
Time-resolved photoelectron spectroscopy combines femtosecond pump-probe techniques with angle-resolved photoelectron spectroscopy (ARPES). New opportunities for this powerful technique arise in combination with THz excitation. As an example, I will explain how THz-ARPES can be used to measure electron transport in the Dirac surface state of a three-dimensional topological insulator in a contact-free fashion and with femtosecond time-resolution. We induce electrical currents in these states with strong THz transients and directly access their dynamics in momentum space with subcycle time resolution. As a result of spin-momentum locking, the accelerated spin-polarized electrons reach ballistic mean free paths of several hundreds of nanometers. Topological insulators are thus promising materials for future lightwave-driven electronics [1].
Subcycle THz-ARPES does not only provide a way of observing carrier transport directly in non-trivial band structures. The method may well herald a new era of time-domain investigations of surface and bulk band structures of new materials and phenomena, ranging from topology to high-temperature superconductivity. I will briefly discuss perspectives as well as experimental difficulties of the technique.
[1] J. Reimann, S. Schlauderer, C. P. Schmid, F. Langer, S. Baierl, K. A. Kokh, O. E. Tereshchenko, A. Kimura, C. Lange, J. Güdde, U. Höfer, and R. Huber, Nature 562, 396 (2018).講師紹介
Ulrich Höfer 先生は、表面物理科学の分野で世界的に著名な研究者です。主に時間分解二光子光電子分光を用いた固体表面・界面電子や吸着分子が示す超高速な光励起ダイナミクスを対象とした研究を展開されています。談話会では、先生の研究グループが世界で初めて成功したテラヘルツポンプ角度分解光電子分光について解説して頂く予定です。物性研における光科学・表面科学そしてそれらの融合研究との関連性も深い内容で、興味深いお話が伺えると思います。是非、皆様ご参加下さい。