Tracking Primary Thermalization Events in Graphene with Photoemission at Extreme Time Scales.
Direct and inverse Auger scattering are amongst the primary processes that mediate the thermalization of hot carriers in semiconductors. These two processes involve the annihilation or generation of an electron-hole pair by exchanging energy with a third carrier, which is either accelerated or decelerated. Inverse Auger scattering is generally suppressed, as the decelerated carriers must have excess energies higher than the band gap itself. In graphene, which is gapless, inverse Auger scattering is, instead, predicted to be dominant at the earliest time delays. Here, <8  fs extreme-ultraviolet pulses are used to detect this imbalance, tracking both the number of excited electrons and their kinetic energy with time-and angle-resolved photoemission spectroscopy. Over a time window of approximately 25 fs after absorption of the pump pulse, we observe an increase in conduction band carrier density and a simultaneous decrease of the average carrier kinetic energy, revealing that relaxation is in fact dominated by inverse Auger scattering. Measurements of carrier scattering at extreme time scales by photoemission will serve as a guide to ultrafast control of electronic properties in solids for petahertz electronics.
Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, 22761 Hamburg, Germany.
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Gierz
Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, 22761 Hamburg, Germany.|Institute for Photonics and Nanotechnologies, IFN-CNR, 20133 Milano, Italy.
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Calegari
Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, 22761 Hamburg, Germany.
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Aeschlimann
Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, 22761 Hamburg, Germany.
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Chávez Cervantes
Central Laser Facility, STFC Rutherford Appleton Laboratory, OX11 0QX Harwell, United Kingdom.
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Cacho
Central Laser Facility, STFC Rutherford Appleton Laboratory, OX11 0QX Harwell, United Kingdom.
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Chapman
Central Laser Facility, STFC Rutherford Appleton Laboratory, OX11 0QX Harwell, United Kingdom.
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Springate
Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany.
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Link
Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany.
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Starke
Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany.
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Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, 22761 Hamburg, Germany.|Department of Physics, Clarendon Laboratory, University of Oxford, OX1 3PU Oxford, United Kingdom.
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Cavalleri