电荷密度波材料长时泵探实验的理论描述

IF 11.6 1区 物理与天体物理 Q1 PHYSICS, MULTIDISCIPLINARY
Marko D. Petrović, Manuel Weber, James K. Freericks
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引用次数: 0

摘要

我们使用经典蒙特卡洛方法半经典地描述了耦合非平衡电子-声子系统-声子的赫伦费斯特动力学和电子的量子力学,该方法确定了对大泵场的非平衡响应。由于声子被激发的平均能量远高于声子频率,因此无需量子描述,因此半经典方法有望获得精确结果。这种方法的数值效率使我们能够在很长的时间内(几十皮秒)进行自洽的时间演化,从而能够模拟电荷密度波(CDW)材料的泵探实验。我们的系统是一个半填充的一维(1D)荷斯坦链,它因佩尔斯转变而表现出 CDW 有序性。该链受到一个随时间变化的电磁泵场的激励,使其脱离平衡状态,然后在延时后施加第二个探测脉冲。通过长时间演化系统,我们捕捉到了晶格激发和随后弛豫到新平衡的完整过程,这是由于电子和晶格之间的能量交换,导致晶格在有限温度下弛豫。我们采用了泵脉冲对晶格的间接(脉冲)驱动机制,而不是电子的直接驱动。我们确定了两种驱动机制,在这两种机制中,泵可以引起微小的扰动,也可以完全颠倒初始的 CDW 秩。我们的研究成功地描述了 CDW 系统中振幅模式的振铃现象,这种现象在实验中早已出现,但从未用微观理论成功解释过。我们还描述了反转 CDW 秩参数并改变声子动力学的随通量变化的交叉。最后,我们说明了这种方法如何能检查许多不同类型的实验,包括光发射、X 射线衍射和二维(2D)光谱。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Theoretical Description of Pump-Probe Experiments in Charge-Density-Wave Materials out to Long Times

Theoretical Description of Pump-Probe Experiments in Charge-Density-Wave Materials out to Long Times
We describe coupled nonequilibrium electron-phonon systems semiclassically—Ehrenfest dynamics for the phonons and quantum mechanics for the electrons—using a classical Monte Carlo approach that determines the nonequilibrium response to a large pump field. The semiclassical approach is expected to be accurate, because the phonons are excited to average energies much higher than the phonon frequency, eliminating the need for a quantum description. The numerical efficiency of this method allows us to perform a self-consistent time evolution out to very long times (tens of picoseconds), enabling us to model pump-probe experiments of a charge-density-wave (CDW) material. Our system is a half-filled, one-dimensional (1D) Holstein chain that exhibits CDW ordering due to a Peierls transition. The chain is subjected to a time-dependent electromagnetic pump field that excites it out of equilibrium, and then a second probe pulse is applied after a time delay. By evolving the system to long times, we capture the complete process of lattice excitation and subsequent relaxation to a new equilibrium, due to an exchange of energy between the electrons and the lattice, leading to lattice relaxation at finite temperatures. We employ an indirect (impulsive) driving mechanism of the lattice by the pump pulse due to the direct driving of the electrons. We identify two driving regimes, where the pump can either cause small perturbations or completely invert the initial CDW order. Our work successfully describes the ringing of the amplitude mode in CDW systems that has long been seen in experiment but never successfully explained by microscopic theory. We also describe the fluence-dependent crossover that inverts the CDW order parameter and changes the phonon dynamics. Finally, we illustrate how this method can examine a number of different types of experiments including photoemission, x-ray diffraction, and two-dimensional (2D) spectroscopy.
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来源期刊
Physical Review X
Physical Review X PHYSICS, MULTIDISCIPLINARY-
CiteScore
24.60
自引率
1.60%
发文量
197
审稿时长
3 months
期刊介绍: Physical Review X (PRX) stands as an exclusively online, fully open-access journal, emphasizing innovation, quality, and enduring impact in the scientific content it disseminates. Devoted to showcasing a curated selection of papers from pure, applied, and interdisciplinary physics, PRX aims to feature work with the potential to shape current and future research while leaving a lasting and profound impact in their respective fields. Encompassing the entire spectrum of physics subject areas, PRX places a special focus on groundbreaking interdisciplinary research with broad-reaching influence.
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