YTiO$_3$中涨落高温铁磁性的光学稳定化
Optical Stabilization of Fluctuating High Temperature Ferromagnetism in YTiO$_3$
AI总结：
本文提出利用全光学模式选择性操控晶格，增强并稳定YTiO$_3$中的高温铁磁性，通过激发9 THz氧旋转模式实现瞬态铁磁性并揭示其源于非线性声子-轨道-自旋耦合的动态机制。
摘要：
在量子材料中，简并与阻挫相互作用会对长程序的产生产生深远影响，通常会引起强烈的涨落，从而抑制与功能相关的电子或磁相。在体相或异质界面处工程化原子结构一直是消除这些简并的重要研究策略，但这些平衡方法受到热力学、弹性和化学约束的限制。在此，我们展示了对晶格的全光学、模式选择性操控可用于增强并稳定YTiO$_3$中的高温铁磁性，该材料仅表现出部分轨道极化、未饱和的低温磁矩以及受抑制的居里温度，$T_c$ = 27 K。当激发9 THz的氧旋转模式时，增强效果最为显著，在低温下实现了完全的磁饱和，并在高达$T_{neq} >$ 80 K时实现了瞬态铁磁性，这几乎是热力学转变温度的三倍。非线性声子-轨道-自旋耦合的第一性原理和模型计算表明，这些效应源于轨道极化的动态变化以及最低准简并Ti $t_{2g}$能级的构成。值得注意的是，YTiO$_3$中光致高温铁磁性被发现可在多个纳秒内保持亚稳态，这凸显了动态工程化实用非平衡功能性的能力。
英文摘要：
In quantum materials, degeneracies and frustrated interactions can have a profound impact on the emergence of long-range order, often driving strong fluctuations that suppress functionally relevant electronic or magnetic phases. Engineering the atomic structure in the bulk or at heterointerfaces has been an important research strategy to lift these degeneracies, but these equilibrium methods are limited by thermodynamic, elastic, and chemical constraints. Here, we show that all-optical, mode-selective manipulation of the crystal lattice can be used to enhance and stabilize high-temperature ferromagnetism in YTiO$_3$, a material that exhibits only partial orbital polarization, an unsaturated low-temperature magnetic moment, and a suppressed Curie temperature, $T_c$ = 27 K. The enhancement is largest when exciting a 9 THz oxygen rotation mode, for which complete magnetic saturation is achieved at low temperatures and transient ferromagnetism is realized up to $T_{neq} >$ 80 K, nearly three times the thermodynamic transition temperature. First-principles and model calculations of the nonlinear phonon-orbital-spin coupling reveal that these effects originate from dynamical changes to the orbital polarization and the makeup of the lowest quasi-degenerate Ti $t_{2g}$ levels. Notably, light-induced high temperature ferromagnetism in YTiO$_3$ is found to be metastable over many nanoseconds, underscoring the ability to dynamically engineer practically useful non-equilibrium functionalities.
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