Long-lived photoinduced response observed under extreme photoexcitation densities in a one-dimensional Peierls insulator

Johanna W. Wolfson, Samuel W. Teitelbaum, Taeho Shin, Ikufumi Katayama, Taro Kawano, Jun Takeda, and Keith A. Nelson

Phys. Rev. B 98, 054111 – Published 27 August 2018

Abstract

One-dimensional metal-halide compounds provide model systems to investigate the manner in which coupling between elementary degrees of freedom—here, electronic and vibrational—result in instabilities that give rise to both chemical and structural rearrangements. Here, we employ “single-shot” pump-probe spectroscopy to examine a one-dimensional platinum iodide compound (PtI(en)) under far-from-equilibrium conditions where repeated photoexcitation results in sample damage. It presents evidence for a distinct collective excited state lasting more than 100 ps upon self-trapped exciton generation at high densities, as measured by electronic signal amplitudes and phonon properties.

Received 14 February 2018
Revised 5 August 2018

DOI:https://doi.org/10.1103/PhysRevB.98.054111

Physics Subject Headings (PhySH)

Charge density waves Electron-phonon coupling Peierls transition Phase transitions Phonons Polarons Ultrafast phenomena

1-dimensional systems

Ultrafast pump-probe spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Johanna W. Wolfson¹, Samuel W. Teitelbaum¹, Taeho Shin², Ikufumi Katayama³, Taro Kawano³, Jun Takeda³, and Keith A. Nelson^1,*

¹Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
²Department of Chemistry, Chonbuk National University, Jeonju 54896, Republic of Korea
³Graduate School of Engineering, Yokohama National University, Yokohama 240-8501, Japan

^*kanelson@mit.edu

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Vol. 98, Iss. 5 — 1 August 2018

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Images

Figure 1
(a) Simplified schematic illustration of the crystal structure of ${[PtI {(en)}_{2}]}_{2} {({ClO}_{4})}_{4}$ . Pt and I atoms are arranged in 1D chains with alternating ${Pt}^{2 +}$ and ${Pt}^{4 +}$ ions and alternating Pt-I bond lengths (exaggerated). Perchlorate counterions (not shown) neutralize the net-positive charge of the 1D chains. (b) Schematic illustration of the formation of a self-trapped exciton (STE) in PtI(en), as viewed along the PtI chains. In the highly localized (small polaron) limit, a charge-transfer transition generates a pair of ${Pt}^{3 +}$ ions, exciting a Raman-active vibration along the chain axis and equalizing Pt-I bond lengths. This is a simplified picture, and it is predicted that the STE is delocalized over several unit cells, and the charge separation is a fraction of an electron $[δ = 0.36 e^{-}$ in PtI(en)] [11]. Figure adapted from [12, 13].
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Figure 2
(a) Reversible pump-probe traces of PtI(en) at low fluence (from 0.2 to $1.6 mJ / {cm}^{2})$ . The pump and probe wavelengths are both 800 nm. (b) Fluence dependence of the reflectivity change at $t = 0$ of the traces shown in (a) (blue points). The dashed line shows an exponential fit to the fluence dependence.
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Figure 3
(a) Reflectivity changes at various pump fluences obtained conventional pump-probe measurements with over $10^{6}$ shots. (b) After preirradiation with pump fluence used in (a), reflectivity changes were obtained at the same spots under low pump fluence of 1. $6 mJ / {cm}^{2}$ . The same colors of curves in (a) and (b) indicate the same spots for both measurements. For preirradiation above 2. $4 mJ / {cm}^{2}$ with over $10^{6}$ shots, the sample shows irreversible damage, demonstrating the need for single-shot measurements. (c) Single-shot pump-probe data at various pump fluences below and above the damage threshold. The small feature before $t = 0$ is due to a prepulse in the amplifier. (d)–(f) Fit parameters showing fluence dependence of phonon properties, the oscillation amplitude relative to the total reflectivity change at $t = 0$ (d), oscillation frequency (e), and oscillation dephasing time (f) of the coherent phonon oscillation. The coherent phonon signal disappears at $12 mJ / {cm}^{2}$ . The error bars in (d)–(f) represent the uncertainty from the fitting analysis.
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Figure 4
Double-pump experiments performed with a $0.8 − mJ / {cm}^{2}$ second pump pulse reveal dynamics of the highly excited state. (a) Double-pump response with an initial excitation fluence of $12 mJ / {cm}^{2}$ at various interpump delays. (b)–(e) Show fit parameters for the pump-probe response to the second pump as a function of interpump delay for 1.4, 4.5, and $12 mJ / {cm}^{2}$ first-pulse fluence. The parameters shown are the nonoscillatory amplitude (b), the oscillation amplitude (c), the oscillation frequency (d), and the dephasing time (e). Infinite time corresponds to a measurement taken long after the second pump, approximately 1 min later. The error bars in (b)–(e) represent the uncertainty generated from the fitting analysis.
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