Momentum-Resolved Spin Dynamics of Bulk and Surface Excited States in the Topological Insulator Bi2Se3

C. Cacho, A. Crepaldi, M. Battiato, J. Braun, F. Cilento, M. Zacchigna, M. C. Richter, O. Heckmann, E. Springate, Y. Liu, S. S. Dhesi, H. Berger, Ph. Bugnon, K. Held, M. Grioni, H. Ebert, K. Hricovini, J. Minár, and F. Parmigiani
Phys. Rev. Lett. 114, 097401 – Published 4 March 2015
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Abstract

The prospect of optically inducing and controlling a spin-polarized current in spintronic devices has generated wide interest in the out-of-equilibrium electronic and spin structure of topological insulators. In this Letter we show that only measuring the spin intensity signal over several orders of magnitude by spin-, time-, and angle-resolved photoemission spectroscopy can provide a comprehensive description of the optically excited electronic states in Bi2Se3. Our experiments reveal the existence of a surface resonance state in the second bulk band gap that is benchmarked by fully relativistic ab initio spin-resolved photoemission calculations. We propose that the newly reported state plays a major role in the ultrafast dynamics of the system, acting as a bottleneck for the interaction between the topologically protected surface state and the bulk conduction band. In fact, the spin-polarization dynamics in momentum space show that these states display macroscopically different temperatures and, more importantly, different cooling rates over several picoseconds.

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  • Received 15 September 2014

DOI:https://doi.org/10.1103/PhysRevLett.114.097401

© 2015 American Physical Society

Authors & Affiliations

C. Cacho1, A. Crepaldi2, M. Battiato3, J. Braun4, F. Cilento2, M. Zacchigna5, M. C. Richter6,7, O. Heckmann6,7, E. Springate1, Y. Liu8, S. S. Dhesi8, H. Berger9, Ph. Bugnon9, K. Held3, M. Grioni9, H. Ebert4, K. Hricovini6,7, J. Minár4,10, and F. Parmigiani2,11,12,*

  • 1Central Laser Facility, STFC Rutherford Appleton Laboratory, Harwell OX11 0QX, United Kingdom
  • 2Elettra–Sincrotrone Trieste S. C. p. A., Strada Statale 14, km 163.5, 34149 Basovizza, Trieste, Italy
  • 3Institute of Solid State Physics, Vienna University of Technology, Wiedner Hauptstrasse 8-10, A 1040 Wien, Austria
  • 4Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse 5-13, 81377 München, Germany
  • 5CNR–IOM, Strada Statale 14, km 163.5, Trieste 34149, Italy
  • 6Laboratoire de Physique des Matriaux et des Surfaces, Université de Cergy-Pontoise, 5 mail Gay-Lussac, 95031 Cergy-Pontoise, France
  • 7DSM, IRAMIS, Service de Physique de l’Etat Condensé, CEA-Saclay, 91191 Gif-sur-Yvette, France
  • 8Diamond Light Source, Chilton, Didcot, Oxfordshire OX110DE, United Kingdom
  • 9Institute of Condensed Matter Physics (ICMP), École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
  • 10New Technologies-Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen, Czech Republic
  • 11Università degli Studi di Trieste, Via A. Valerio 2, Trieste 34127, Italy
  • 12International Faculty, University of Köln, 50937 Köln, Germany

  • *fulvio.parmigiani@elettra.eu

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Issue

Vol. 114, Iss. 9 — 6 March 2015

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