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arXiv 2402.01247cond-mat.str-el
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二氧化钒中的光致相变:张量网络研究

Light-induced phase transitions in vanadium dioxide: a tensor network study

Lin Zhang, Utso Bhattacharya, Maria Recasens, Tobias Grass, Ravindra W. Chhajlany, Maciej Lewenstein, Allan S. Johnson

AI总结:

本研究利用混合量子-经典张量网络方法模拟VO2的光致相变,揭示了晶格非线性导致的非单调转化路径以及结构相变与绝缘体-金属转变解耦的动力学机制。

摘要:

由光脉冲驱动的非平衡相变代表了凝聚态物理学中一个快速发展的领域。作为典型的强关联材料之一,二氧化钒(VO2)在被加热至340 K以上或被超快激光脉冲激发时,会经历从单斜(M1)到金红石(R)结构的结构相变(SPT)以及绝缘体到金属的转变(IMT)。在此,我们提出了一种基于准一维模型的VO2光致相变张量网络研究,该模型包含了所有重要成分——多轨道特性、电子-晶格耦合以及电子-电子关联。我们展示了通过计算基态相图和有限温度相变,该模型定性上捕捉了VO2的平衡性质。我们使用一种混合量子-经典张量网络方法来模拟光激发后的动力学。我们发现结构的转化速度可以快于M1相的简谐声子模式,这表明晶格非线性在SPT中起关键作用。我们还发现晶格动力学中二聚化和倾斜畸变演化具有不同的时间尺度,以及位移的丢失和随后部分恢复的行为,这可以为近期实验中观察到的复杂动力学提供解释 [C. Brahms 等,arXiv:XXXX.XXXXX]。此外,在数值模拟中观察到了SPT和IMT动力学的解耦:虽然初始的M1结构在几十飞秒内转变为R结构,但IMT是准瞬间发生的,这与最近的实验发现一致。我们的理论研究为VO2的光致相变提供了见解,揭示了出乎意料的非单调转化路径,并为未来的非热相变研究铺平了道路。

英文摘要:

Nonequilibrium phase transitions driven by light pulses represent a rapidly developing field in condensed matter physics. As one of the archetypal strongly correlated materials, vanadium dioxide (VO2) undergoes a structural phase transition (SPT) from a monoclinic (M1) to rutile (R) structure and an insulator-to-metal transition (IMT) either when heated above 340 K or when excited by an ultrafast laser pulse. Here, we present a tensor network study of the light-induced phase transitions in VO2 based on a quasi-one-dimensional model with all the important ingredients -- multi-orbital character, electron-lattice coupling, and electron-electron correlations -- being included. We show that this model qualitatively captures the equilibrium properties of VO2 by calculating the ground state phase diagram and finite-temperature phase transitions. A hybrid quantum-classical tensor-network method is used to simulate the dynamics following photoexcitation. We find that the structure can transform faster than the harmonic phonon modes of M1 phase, suggesting lattice nonlinearity is key in the SPT. We also find separate timescales for the evolution of dimerization and tilt distortions in the lattice dynamics, as well as the loss and subsequent partial restoration behavior of the displacements, which can provide an explanation for the complex dynamics observed in recent experiments [C. Brahms et al., arXiv:XXXX.XXXXX]. Moreover, decoupled SPT and IMT dynamics are observed in the numerical simulations: while the initial M1 structure transforms to the R one in tens of femtoseconds, the IMT occurs quasi-instantaneously, consistent with recent experimental findings. Our theoretical studies provide insight into the light-induced phase transitions of VO2, revealing unexpected non-monotonic transformation pathways and paving the way for future studies of non-thermal phase transformations.

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