Observation of Terahertz Spin Hall Conductivity Spectrum in GaAs with Optical Spin Injection

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Observation of Terahertz Spin Hall Conductivity Spectrum in GaAs with Optical Spin Injection

Tomohiro Fujimoto, Takayuki Kurihara, Yuta Murotani, Tomohiro Tamaya, Natsuki Kanda, Changsu Kim, Jun Yoshinobu, Hidefumi Akiyama, Takeo Kato, and Ryusuke Matsunaga

Phys. Rev. Lett. 132, 016301 – Published 4 January 2024

Abstract

We report the first observation of the spin Hall conductivity spectrum in GaAs at room temperature. Our terahertz polarimetry with a precision of several $μ rad$ s resolves the Faraday rotation of terahertz pulses arising from the inverse spin Hall effect of optically injected spin-polarized electrons. The obtained spin Hall conductivity spectrum exhibits an excellent quantitative agreement with theory, demonstrating a crossover in the dominant origin from impurity scattering in the dc regime to the intrinsic Berry-curvature mechanism in the terahertz regime. Our spectroscopic technique opens a new pathway to analyze anomalous transports related to spin, valley, or orbital degrees of freedom.

Received 16 May 2023
Accepted 21 November 2023

DOI:https://doi.org/10.1103/PhysRevLett.132.016301

Physics Subject Headings (PhySH)

Inverse spin Hall effect Spin Hall effect

III-V semiconductors

Terahertz spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Tomohiro Fujimoto ^*, Takayuki Kurihara , Yuta Murotani , Tomohiro Tamaya , Natsuki Kanda , Changsu Kim , Jun Yoshinobu , Hidefumi Akiyama , Takeo Kato , and Ryusuke Matsunaga ^†

The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan

^*fujimoto@issp.u-tokyo.ac.jp
^†matsunaga@issp.u-tokyo.ac.jp

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Vol. 132, Iss. 1 — 5 January 2024

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Images

Figure 1
(a) Schematic of the optical system. A circularly polarized pump pulse excites the sample, and the Faraday rotation of the THz probe pulse is detected by electro-optic sampling with a (110) GaP crystal. Both pulses are normally incident on the sample. (b) Schematic of the experimental configuration in the sample. $σ_{+}$ denotes the LCP pump, exciting spin-polarized electrons with $N_{↓} / N_{↑} = 3$ . When the $x$ -polarized THz field $E_{x}$ is applied, the net charge current $J_{y}$ is generated by the ISHE. Inset shows the selection rule of the interband transitions by the circularly polarized pump.
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Figure 2
(a) Schematic of the relation between the pump, probe, and gate pulses. (b) (upper) THz electric field waveform $E_{x} (t_{1})$ transmitting through the sample without the pump. (lower) 2D plot of the THz electric field $E_{x} (t_{1}, t_{2})$ across the pump pulse irradiation around $t_{2} \sim 0$ ps with a pump fluence of $109 μ J {cm}^{- 2}$ and a pump photon energy of 1.46 eV. (c) Solid circles show light-induced longitudinal conductivity spectrum $Δ σ_{x x} (ω)$ at $t_{2} = 5.0 ps$ with a pump fluence of $1 9.7 μ J {cm}^{- 2}$ , whereas the solid curves show the Drude model fitting. Error bars represent statistical errors. (d),(e) Carrier density estimated from the Drude fitting as a function of the pump fluence at $t_{2} = 5.0 ps$ , and the pump delay $t_{2}$ with a pump fluence of $179 μ J {cm}^{- 2}$ , respectively.
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Figure 3
(a) 2D plot of the light-induced $y$ -polarized electric field $Δ E_{y}$ as a function of $t_{1}$ and $t_{2}$ with a pump fluence of $1 8.3 μ J {cm}^{- 2}$ and a pump photon energy of 1.55 eV. (b),(c) Decay dynamics of $Δ E_{y}$ for $t_{1} = 0.1 2$ and 0.30 ps, respectively; the solid curves show the fitting results. (d) Upper and lower panels show the decay times as a function of the pump fluence for the data in (b) and (c), respectively.
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Figure 4
(a),(b) Solid circles show the experimental results of real and imaginary parts of the spin Hall conductivity spectrum $σ_{y x}^{SH} (ω)$ , respectively. Error bars represent statistical errors. Solid curves show the theoretical curves for $τ_{ex} = 250 fs$ , using Eqs. (2)–(4). The pump photon energy is 1.46 eV and the fluence is $1 9.7 μ J {cm}^{- 2}$ . (c),(d) Solid curves show the theoretical curves for various $τ_{ex}$ . (e),(f) Each microscopic contribution of the spin Hall conductivity for $τ_{ex} = 250 f s$ . Int, SJ, and SS stand for the intrinsic, side-jump, and skew scattering mechanisms, respectively.
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