Electron spin coherence dynamics in CdS crystals
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摘要: 利用时间分辨克尔旋转(Time-Resolved Kerr Rotation, TRKR)光谱技术研究了纤锌矿n-CdS(n型掺杂)(0001)面单晶在不同温度、不同波长下的电子自旋相干动力学. 发现低温下该材料存在两种电子自旋信号: 一种是在较长泵浦探测波长下存在的长寿命自旋信号, 低温5 K时其自旋退相位时间长达4.8 ns, 随着温度的升高不断减小; 另一种为较短泵浦探测波长下存在的短寿命自旋信号, 其自旋退相位时间约为40 ps, 可以持续到室温, 该自旋信号几乎不受温度的影响. 研究表明, 长寿命自旋信号来自于局域电子, 而短寿命自旋信号来自于导带自由电子.Abstract: In this paper, we use time-resolved Kerr rotation(TRKR) spectroscopy to study the electron spin coherence dynamics of a wurtzite (0001) plane n-CdS single crystal at different temperatures and wavelengths. Two types of electronic spin signals are observed in this material at low temperatures. One is a long-lived spin signal at relatively long pump probe wavelengths, where the spin dephasing time exceeds 4.8 ns at 5 K and decreases with increasing temperature. The other is a short-lived spin signal at relatively short pump probe wavelengths, where the spin dephasing time is about 40 ps and persists up to room temperature; in this case, the spin signal is largely independent of temperature. Studies have shown that long-lived spin signals can be attributed to localized electrons, while short-lived spin signals can be attributed to conduction delocalized electrons.
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Key words:
- electron spin /
- CdS /
- single crystal /
- pump-probe
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图 4 克尔旋转信号理论模拟: a)窄谱(黑色虚线)和宽谱(红色实线)探测的克尔旋转信号振幅随波长的依赖性对比; 中心波长分别为 b) 489.8 nm、c) 490.7 nm和 d) 488.2 nm高斯谱线上各位置点所对应的克尔旋转信号
Fig. 4 Theoretical simulation of Kerr rotation signal: a) Comparison of the spectral dependence of Kerr rotation under the narrowband detection pulse (black dotted line) versus the broadband detection pulse (solid red line); Kerr rotation signal corresponding to each point on the Gaussian spectral line with a center wavelength of b) 489.8 nm, c) 490.7 nm, and d) 488.2 nm
图 6 T = 50 K, B = 1 T时: a)、b)不同波长下的时间分辨克尔旋转光谱;c)自旋退相位时间
$T_2^*$ 随波长的依赖; d)拉莫尔进动频率${v_{\rm{L}}}$ 随波长的依赖Fig. 6 a), b) TRKR signals at different wavelengths; c) Dependence of the spin dephasing time,
$T_2^*$ on wavelength; (d) Dependence of the Larmor precession frequency,${v_{\rm{L}}}$ on wavelength; Where T = 50 K, B = 1 T图 8 a)不同温度下自旋退相位时间
$T_2^*$ 随波长的依赖关系; b)发光峰处波长激发的自旋信号退相位时间$T_2^*$ 、拉莫尔进动频率${v_{\rm{L}}}$ 随温度的依赖关系, 插图为发光波长随温度的依赖Fig. 8 a) Wavelength dependence of spin dephasing time,
$T_2^*$ , at different temperatures; b) Temperature dependence of the spin dephasing time,$T_2^*$ , and Larmor precession frequency,${v_{\rm{L}}}$ , at the emission peak wavelength, inset shows the emission peak as a function of temperature -
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