钽酸锂中束缚于间隙钽缺陷的小电子极化子
Small electron polarons bound to interstitial tantalum defects in lithium tantalate
AI总结：
本研究通过光吸收光谱和密度泛函理论，在钽酸锂中发现两个能量分离的小束缚电子极化子吸收特征，证明间隙Ta_V:V_Li缺陷处的载流子局域化是室温三维跳跃传输的额外中间态，影响非线性光子学应用。
摘要：
本文研究了同成分钽酸锂（LiTaO₃，简称LT）中光生、短寿命小束缚电子极化子的吸收特性，旨在探讨是否可能通过强、短程电子-声子耦合将电子局域在间隙Ta_V:V_Li缺陷对处。采用光照下的固态光吸收光谱和密度泛函理论，实验和理论上获取了小束缚极化子态的光谱特征，并计算了小束缚Ta_Li⁴⁺（反位）和Ta_V⁴⁺:V_Li（间隙位）电子极化子的结合能。结果发现了两个能量分离良好（ΔE≈0.5 eV）的吸收特征，它们对探测光偏振具有明显依赖性，分别在1.6 eV和2.1 eV处达到峰值。我们将结果与单一小束缚Ta_Li⁴⁺电子态伴随强晶格畸变各向异性的解释进行了对比，并在Ta_V⁴⁺:Ta_Ta⁴⁺双极化子光门控的框架下讨论了间隙Ta_V⁴⁺:V_Li小极化子的光生机制。我们得出结论，除了Ta_Li之外，Ta_V:V_Li处的载流子局域化也必须被视为室温下三维跳跃传输机制的额外中间态，从而影响LT在非线性光子学中的多种光学、光电和电学应用。此外，预计LT将成为进一步研究极性氧化物中基于小极化子的光生伏特效应的有前景模型系统，其独特特征在于拥有两个能量分离良好的小极化子态。
英文摘要：
The absorption features of optically generated, short-lived small bound electron polarons are inspected in congruent lithium tantalate, ${\rm LiTaO}_3$ (LT), in order to address the question whether it is possible to localize electrons at interstitial ${\rm Ta_V}$:${\rm V_{Li}}$ defect pairs by strong, short-range electron-phonon coupling. Solid-state photoabsorption spectroscopy under light exposure and density functional theory are used for an experimental and theoretical access to the spectral features of small bound polaron states and to calculate the binding energies of the small bound ${\rm Ta}_{\rm Li}^{4+}$ (antisite) and ${\rm Ta}_{\rm V}^{4+}$:${\rm V_{Li}}$ (interstitial site) electron polarons. As a result, two energetically well separated ($ΔE \approx 0.5\,{\rm eV}$) absorption features with a distinct dependence on the probe light polarization and peaking at $1.6\,{\rm eV}$ and $2.1\,{\rm eV}$ are discovered. We contrast our results to the interpretation of a single small bound ${\rm Ta}_{\rm Li}^{4+}$ electron state with strong anisotropy of the lattice distortion and discuss the optical generation of interstitial ${\rm Ta}_{\rm V}^{4+}$:${\rm V_{Li}}$ small polarons in the framework of optical gating of ${\rm Ta}_{\rm V}^{4+}$:${\rm Ta}_{\rm Ta}^{4+}$ bipolarons. We can conclude that the appearance of carrier localization at $\mathrm{Ta_V}$:${\rm V_{Li}}$ must be considered as additional intermediate state for the 3D hopping transport mechanisms at room temperature in addition to ${\rm Ta_{Li}}$, as well, and, thus, impacts a variety of optical, photoelectrical and electrical applications of LT in nonlinear photonics. Furthermore, it is envisaged that LT represents a promising model system for the further examination of the small-polaron based photogalvanic effect in polar oxides with the unique feature of two, energetically well separated small polaron states.
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