Experimental study of electron-phonon coupling and electron internal thermalization in epitaxially grown ultrathin copper films

Shen, Xin; Timalsina, Yukta P.; Lu, Toh‐Ming; Yamaguchi, Masashi

doi:10.1103/physrevb.91.045129

Cited by 25 publications

(25 citation statements)

References 36 publications

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“…The background signal of the transient reflectivity relaxes to an equilibrium value within a few picoseconds regardless of the orientation of the sample, indicating the isotropic nature of the initial peak and the following decay. The possible origin of the non-oscillating background decay is energy relaxation of electrons from a non-equilibrium state to a quasi-equilibrium state in which electrons are thermalized through electron-electron interaction3637. The behavior of this background component is quite different from the reported optically excited phonons in GaAs1718 where the background component decays in slower time-scale of carrier recombination of nanosecond383940.…”

Section: Resultsmentioning

confidence: 99%

Coherent Excitation of Optical Phonons in GaAs by Broadband Terahertz Pulses

Yamaguchi

2016

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Coherent excitation and control of lattice motion by electromagnetic radiation in optical frequency range has been reported through variety of indirect interaction mechanisms with phonon modes. However, coherent phonon excitation by direct interaction of electromagnetic radiation and nuclei has not been demonstrated experimentally in terahertz (THz) frequency range mainly due to the lack of THz emitters with broad bandwidth suitable for the purpose. We report the experimental observation of coherent phonon excitation and detection in GaAs using ultrafast THz-pump/optical-probe scheme. From the results of THz pump field dependence, pump/probe polarization dependence, and crystal orientation dependence, we attributed THz wave absorption and linear electro-optic effect to the excitation and detection mechanisms of coherent polar TO phonons. Furthermore, the carrier density dependence of the interaction of coherent phonons and free carriers is reported.

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Section: Resultsmentioning

confidence: 99%

Coherent Excitation of Optical Phonons in GaAs by Broadband Terahertz Pulses

Yamaguchi

2016

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“…For example, it is difficult and in some cases even impossible to unambiguously disentangle the different contributions of measured reflectivity transients after short pulse laser excitation since they can depend critically on the experimental parameters (e.g. probe wavelength [13]).…”

Section: Introductionmentioning

confidence: 99%

Thickness-dependent electron–lattice equilibration in laser-excited thin bismuth films

Sokolowski‐Tinten

Reid

et al. 2015

New J. Phys.

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“…To conclude, by combining the first-principles calculations of carrier dynamics and optical response, this Letter presents a complete theoretical description of pump-probe measurements, free of any fitting parameters that are typical in previous analyses [35,[47][48][49]. The theory here accounts for detailed energy distributions of excited carriers (Fig.…”

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confidence: 99%

“…The initial response additionally includes contributions from short-lived highly nonthermal carriers excited initially, which become particularly important at low pump powers when smaller temperature changes limit the thermal contribution. Higher-energy nonthermal carriers exhibit faster rise and decay times than the thermal carriers closer to the Fermi level [26,35], due to higher electron-electron scattering rates. Their response also spans a greater range in probe wavelength compared to thermal electrons, which primarily affect only the resonant d band to Fermi level transition [26,33,46], Combining ab initio predictions and experimental measurements of 60-nm colloidal PRL 118, 087401 (2017) P…”

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confidence: 99%

“…Recent literature has focused on the contributions of thermalized and nonthermalized electrons to the optical signal in pump-probe measurements using free-electronlike theoretical models to interpret optical signatures [20,26,[35][36][37][38]. However, these models invariably require empirical parameters for both the dynamics and response of the electrons, making unambiguous interpretation of experiments challenging.…”

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Experimental and Ab Initio Ultrafast Carrier Dynamics in Plasmonic Nanoparticles

et al. 2017

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Ultrafast pump-probe measurements of plasmonic nanostructures probe the nonequilibrium behavior of excited carriers, which involves several competing effects obscured in typical empirical analyses. Here we present pump-probe measurements of plasmonic nanoparticles along with a complete theoretical description based on first-principles calculations of carrier dynamics and optical response, free of any fitting parameters. We account for detailed electronic-structure effects in the density of states, excited carrier distributions, electron-phonon coupling, and dielectric functions that allow us to avoid effective electron temperature approximations. Using this calculation method, we obtain excellent quantitative agreement with spectral and temporal features in transient-absorption measurements. In both our experiments and calculations, we identify the two major contributions of the initial response with distinct signatures: short-lived highly nonthermal excited carriers and longer-lived thermalizing carriers. DOI: 10.1103/PhysRevLett.118.087401 Plasmonic hot carriers provide tremendous opportunities for combining efficient light capture with energy conversion [1][2][3][4][5] and catalysis [6,7] at the nanoscale [8][9][10]. The microscopic mechanisms in plasmon decays across various energy, length, and time scales are still a subject of considerable debate, as seen in recent experimental [11,12] and theoretical literature [13][14][15][16]. The decay of surface plasmons generates hot carriers through several mechanisms, including direct interband transitions, phonon-assisted intraband transitions, and geometry-assisted intraband transitions, as we have shown in previous work [17,18].Dynamics of hot carriers are typically studied via ultrafast pump-probe measurements of plasmonic nanostructures using a high-intensity laser pulse to excite a large number of electrons and measure the optical response as a function of time using a delayed probe pulse [11,[19][20][21][22][23][24][25]. Various studies have taken advantage of this technique to investigate electron-electron scattering, electron-phonon coupling, and electronic transport [20,22,[26][27][28][29][30][31][32]. Figure 1 shows a representative map of the differential extinction cross section as a function of pump-probe delay time and probe wavelength. With an increase in electron temperature, the real part of the dielectric function near the resonant frequency becomes more negative, while the imaginary part increases [33]. This causes the resonance to broaden and blueshift at short times as the electron temperature rises rapidly, and then to narrow and shift back over longer times as electrons cool down, consistent with previous observations [34]. Taking a slice of the map at one probe wavelength reveals the temporal behavior of the electron relaxation [ Fig. 1(b)], whereas a slice of the map at one time gives the spectral response, as shown in Fig. 1(a) for a set of times relative to the delay time with maximum signal, t max ¼ 700 fs.Conventional analyses of pu...

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Experimental study of electron-phonon coupling and electron internal thermalization in epitaxially grown ultrathin copper films

Cited by 25 publications

References 36 publications

Coherent Excitation of Optical Phonons in GaAs by Broadband Terahertz Pulses

Coherent Excitation of Optical Phonons in GaAs by Broadband Terahertz Pulses

Thickness-dependent electron–lattice equilibration in laser-excited thin bismuth films

Experimental and Ab Initio Ultrafast Carrier Dynamics in Plasmonic Nanoparticles

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