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Nat Commun. 2016 Oct 4;7:12902. doi: 10.1038/ncomms12902.

Self-amplified photo-induced gap quenching in a correlated electron material.

Author information

1
I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany.
2
Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, 67663 Kaiserslautern, Germany.
3
JILA, University of Colorado and NIST, Boulder, Colorado 80309-0440, USA.
4
Institute of Experimental and Applied Physics, University of Kiel, 24098 Kiel, Germany.
5
Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
6
Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.

Abstract

Capturing the dynamic electronic band structure of a correlated material presents a powerful capability for uncovering the complex couplings between the electronic and structural degrees of freedom. When combined with ultrafast laser excitation, new phases of matter can result, since far-from-equilibrium excited states are instantaneously populated. Here, we elucidate a general relation between ultrafast non-equilibrium electron dynamics and the size of the characteristic energy gap in a correlated electron material. We show that carrier multiplication via impact ionization can be one of the most important processes in a gapped material, and that the speed of carrier multiplication critically depends on the size of the energy gap. In the case of the charge-density wave material 1T-TiSe2, our data indicate that carrier multiplication and gap dynamics mutually amplify each other, which explains-on a microscopic level-the extremely fast response of this material to ultrafast optical excitation.

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