Experimental evidence of excited electron number density and temperature effects on electron-phonon coupling in gold films

Ashutosh Giri, John T. Gaskins, Brian Foley, Ramez Cheaito, Patrick E. Hopkins

    Research output: Contribution to journalArticle

    23 Citations (Scopus)

    Abstract

    The electronic transport properties of metals with weak electron-phonon coupling can be influenced by non-thermal electrons. Relaxation processes involving non-thermal electrons competing with the thermalized electron system have led to inconsistencies in the understanding of how electrons scatter and relax with the less energetic lattice. Recent theoretical and computational works have shown that the rate of energy relaxation with the metallic lattice will change depending on the thermalization state of the electrons. Even though 20 years of experimental works have focused on understanding and isolating these electronic relaxation mechanisms with short pulsed irradiation, discrepancies between these existing works have not clearly answered the fundamental question of the competing effects between non-thermal and thermal electrons losing energy to the lattice. In this work, we demonstrate the ability to measure the electron relaxation for varying degrees of both electron-electron and electron-phonon thermalization. This series of measurements of electronic relaxation over a predicted effective electron temperature range up to ∼3500 K and minimum lattice temperatures of 77 K validate recent computational and theoretical works that theorize how a nonequilibrium distribution of electrons transfers energy to the lattice. Utilizing this wide temperature range during pump-probe measurements of electron-phonon relaxation, we explain discrepancies in the past two decades of literature of electronic relaxation rates. We experimentally demonstrate that the electron-phonon coupling factor in gold increases with increasing lattice temperature and laser fluences. Specifically, we show that at low laser fluences corresponding to small electron perturbations, energy relaxation between electrons and phonons is mainly governed by non-thermal electrons, while at higher laser fluences, non-thermal electron scattering with the lattice is less influential on the energy relaxation mechanisms.

    Original languageEnglish (US)
    Article number044305
    JournalJournal of Applied Physics
    Volume117
    Issue number4
    DOIs
    StatePublished - Jan 1 2015

    Fingerprint

    temperature effects
    gold
    electrons
    fluence
    electronics
    electron energy
    lasers
    energy
    temperature
    electron transfer
    electron scattering
    phonons
    transport properties
    pumps

    All Science Journal Classification (ASJC) codes

    • Physics and Astronomy(all)

    Cite this

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    abstract = "The electronic transport properties of metals with weak electron-phonon coupling can be influenced by non-thermal electrons. Relaxation processes involving non-thermal electrons competing with the thermalized electron system have led to inconsistencies in the understanding of how electrons scatter and relax with the less energetic lattice. Recent theoretical and computational works have shown that the rate of energy relaxation with the metallic lattice will change depending on the thermalization state of the electrons. Even though 20 years of experimental works have focused on understanding and isolating these electronic relaxation mechanisms with short pulsed irradiation, discrepancies between these existing works have not clearly answered the fundamental question of the competing effects between non-thermal and thermal electrons losing energy to the lattice. In this work, we demonstrate the ability to measure the electron relaxation for varying degrees of both electron-electron and electron-phonon thermalization. This series of measurements of electronic relaxation over a predicted effective electron temperature range up to ∼3500 K and minimum lattice temperatures of 77 K validate recent computational and theoretical works that theorize how a nonequilibrium distribution of electrons transfers energy to the lattice. Utilizing this wide temperature range during pump-probe measurements of electron-phonon relaxation, we explain discrepancies in the past two decades of literature of electronic relaxation rates. We experimentally demonstrate that the electron-phonon coupling factor in gold increases with increasing lattice temperature and laser fluences. Specifically, we show that at low laser fluences corresponding to small electron perturbations, energy relaxation between electrons and phonons is mainly governed by non-thermal electrons, while at higher laser fluences, non-thermal electron scattering with the lattice is less influential on the energy relaxation mechanisms.",
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    Experimental evidence of excited electron number density and temperature effects on electron-phonon coupling in gold films. / Giri, Ashutosh; Gaskins, John T.; Foley, Brian; Cheaito, Ramez; Hopkins, Patrick E.

    In: Journal of Applied Physics, Vol. 117, No. 4, 044305, 01.01.2015.

    Research output: Contribution to journalArticle

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    AU - Giri, Ashutosh

    AU - Gaskins, John T.

    AU - Foley, Brian

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    AU - Hopkins, Patrick E.

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