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THz-ARPES band structure movies of Dirac surface currents

Date : Friday, November 1st, 2019 4:00 pm - 5:00 pm Place : Lecture Room (A632), 6th Floor, ISSP Lecturer : Prof. Ulrich Höfer Affiliation : Department of Physics, Philipps-University of Marburg, Germany Committee Chair : Taisuke OZAKI, Yasuhiro MATSUDA
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).

(Published on: Thursday September 26th, 2019)