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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.

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


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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