Terahertz pulse induced second harmonic generation and Kerr effect in the quantum paraelectric ${\mathrm{KTaO}}_{3}$

Terahertz pulse induced second harmonic generation and Kerr effect in the quantum paraelectric ${KTaO}_{3}$

Xiaojiang Li, Peisong Peng, Hichem Dammak, Grégory Geneste, Alireza Akbarzadeh, Sergey Prosandeev, L. Bellaiche, and Diyar Talbayev

Phys. Rev. B 107, 064306 – Published 21 February 2023

Abstract

We present a joint experimental and computational study of second harmonic generation and Kerr effect induced by intense terahertz electric fields in the quantum paraelectric material ${KTaO}_{3}$ . The single-cycle terahertz (THz) electric pulses induce the free induction decay of the polar soft phonon mode and a ferroelectric polarization response that lasts for several picoseconds in both experiment and computation. We observe a much longer-lasting (43-ps) transient Kerr effect that follows the THz excitation. We explain the disparity in the relaxation times between the THz-induced second harmonic generation and the Kerr effect by the presence of the polar nanoregions intrinsic to ${KTaO}_{3}$ . The origin of the slow THz Kerr effect dynamics is not presently understood. We speculate that it may be associated with the rotational motion of polar nanoregions due to the material's proximity to the ferroelectric phase transition.

Received 7 November 2022
Revised 9 January 2023
Accepted 7 February 2023

DOI:https://doi.org/10.1103/PhysRevB.107.064306

Physics Subject Headings (PhySH)

Ferroelectricity

Pump-probe spectroscopy Terahertz spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Xiaojiang Li ¹, Peisong Peng ¹, Hichem Dammak ², Grégory Geneste^3,4, Alireza Akbarzadeh^5,6, Sergey Prosandeev⁵, L. Bellaiche⁵, and Diyar Talbayev ^1,*

¹Department of Physics and Engineering Physics, Tulane University, 6400 Freret Street, New Orleans, Louisiana 70118, USA
²Laboratoire SPMS, Université Paris-Saclay, CentraleSupélec, CNRS, F 91190 Gif-sur-Yvette, France
³CEA, DAM, DIF, F-91297 Arpajon, France
⁴Laboratoire Matiére en Conditions Extrêmes, Université Paris-Saclay, CEA, 91680 Bruyéres-le-Châtel, France
⁵Department of Physics, Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, Arkansas 72701, USA
⁶Science, Engineering, and Geosciences, Lonestar College, 9191 Barker Cypress Road, Cypress, Texas 77433, USA

^*dtalbayev@gmail.com

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Vol. 107, Iss. 6 — 1 February 2023

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Figure 1
THz field-induced second harmonic generation spectra. (a) Time-domain spectra under various temperatures with incident THz peak field $E = 210$ kV/cm. The dashed line shows the excitation THz pulse. (b) Frequency domain spectra corresponding to the measurements in (a). First derivatives of the interpolated time-domain spectroscopy were calculated before the Fourier transform to reduce the relative amplitude of the nonoscillatory signal. The inset: Fourier transform of the excitation THz pulse from (a). (c) Frequency domain spectra under various incident peak THz electric fields at 15 K. The inset: Peak values of TFISH time-domain spectra vs peak THz electric field. The red dots show the experimental data, and the blue solid line is the quadratic function.
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Figure 2
THz field-induced Kerr effect spectra. (a) Time-domain TKE spectra under various temperatures with the incident THz peak field of $E = 210$ kV/cm. (b) The frequency domain spectra corresponding to the measurements in (a). (c) Frequency domain spectra under various incident THz electric field at 15 K. The inset: the peak values of TKE time-domain spectra vs peak THz electric field, red dots are the experimental data, and the blue solid line is the quadratic function.
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Figure 3
Long-time range THz field-induced Kerr effect spectra with incident THz peak field $E = 210$ kV/cm. The main figure shows long-time domain TKE spectra vs temperature. The dashed blue lines are the fitting curves with the biexponential function: $f = A e^{\frac{- (t - t_{0})}{τ_{1}}} + B e^{\frac{- (t - t_{0})}{τ_{2}}}$ . The inset (a) shows the extracted relaxation times. The inset (b) shows the relaxation times from TFISH measurements extracted using the exponential function: $f = A e^{\frac{- (t - t_{0})}{τ}}$ .
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Figure 4
Frequency of the polar mode as a function of temperature obtained by RPMD simulations. Experimental results are those from Ref. [49].
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Figure 5
RPMD simulations at 20 K. (a) Effective energy-potential $V (u)$ as a function of the reduced polarization along the [100] direction (blue line) and its harmonic approximation curve (red dashed line). The thermal energy $k_{B} T$ level is shown by the black dotted line. (b) Example of curves $V (u) - E u$ under a static electric field $E$ . (c) Induced polarization as a function of $E$ . (d) frequency of the polar mode (TO) as derived in the harmonic approximation close to the minimum of the $V (u) - E u$ curve.
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Figure 6
Computed dielectric response of KTO to a realistic time-domain THz pulse with an electric field parallel to [100]: panel (a) shows the square of the induced polarization $u^{2}$ (reduced unit) as a function of time in the case of $E_{\max} = 60 kV$ /cm. The realistic THz-field pulse used for the calculation is shown by the dashed blue line. Panels (b) and (c) show the reduced Fourier transform (FT) amplitude of $u^{2}$ in the $0 - 12 − ps$ range, according to the expression (8). Panel (b) is for $E_{\max} = 60 kV$ /cm whereas panel (c) is for different $E_{\max}$ 's for 20 K. The inset in panel (b) shows the FT amplitude of the pulse. The inset in panel (c) shows the integrated intensity in the $0.5 - 5 − THz$ range and its quadratic fit.
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Physical Review B

covering condensed matter and materials physics

Terahertz pulse induced second harmonic generation and Kerr effect in the quantum paraelectric ${KTaO}_{3}$

Xiaojiang Li, Peisong Peng, Hichem Dammak, Grégory Geneste, Alireza Akbarzadeh, Sergey Prosandeev, L. Bellaiche, and Diyar Talbayev

Phys. Rev. B 107, 064306 – Published 21 February 2023

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Physical Review B

covering condensed matter and materials physics

Terahertz pulse induced second harmonic generation and Kerr effect in the quantum paraelectric KTaO3

Xiaojiang Li, Peisong Peng, Hichem Dammak, Grégory Geneste, Alireza Akbarzadeh, Sergey Prosandeev, L. Bellaiche, and Diyar Talbayev

Phys. Rev. B 107, 064306 – Published 21 February 2023

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Terahertz pulse induced second harmonic generation and Kerr effect in the quantum paraelectric ${KTaO}_{3}$