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).