In the last two decades non-equilibrium spectroscopies have evolved from avant-garde studies to crucial tools for expanding our understanding of the physics of strongly correlated materials. The possibility of obtaining simultaneously spectroscopic and temporal information has led to insights that are complementary to (and in several cases beyond) those attainable by studying the matter at equilibrium. From this perspective, multiple phase transitions and new orders arising from competing interactions are benchmark examples where the interplay among electrons, lattice and spin dynamics can be disentangled because of the different timescales that characterize the recovery of the initial ground state. For example, the nature of the broken-symmetry phases and of the bosonic excitations that mediate the electronic interactions, eventually leading to superconductivity or other exotic states, can be revealed by observing the sub-picosecond dynamics of impulsively excited states. Furthermore, recent experimental and theoretical developments have made it possible to monitor the time-evolution of both the single-particle and collective excitations under extreme conditions, such as those arising from strong and selective photo-stimulation. These developments are opening the way for new, non-equilibrium phenomena that can eventually be induced and manipulated by short laser pulses. Here, we review the most recent achievements in the experimental and theoretical studies of the non-equilibrium electronic, optical, structural and magnetic properties of correlated materials. The focus will be mainly on the prototypical case of correlated oxides that exhibit unconventional superconductivity or other exotic phases. The discussion will also extend to other topical systems, such as iron-based and organic superconductors, and charge-transfer insulators. With this review, the dramatically growing demand for novel experimental tools and theoretical methods, models and concepts, will clearly emerge. In particular, the necessity of extending the actual experimental capabilities and the numerical and analytic tools to microscopically treat the non-equilibrium phenomena beyond the simple phenomenological approaches represents one of the most challenging new frontiers in physics.

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强相关材料和高温超导体的超快光谱：一种非平衡方法

在过去的 20 年里，非平衡光谱学已经从前卫的研究发展成为扩展我们对强相关材料物理理解的关键工具。同时获得光谱和时间信息的可能性导致了与通过研究平衡物质可以获得的见解互补（并且在某些情况下超出）。从这个角度来看，多相变和由竞争相互作用产生的新秩序是基准示例，其中电子、晶格和自旋动力学之间的相互作用可以解开，因为表征初始基态恢复的时间尺度不同。例如，破坏对称相和介导电子相互作用的玻色子激发的性质，最终导致超导或其他奇异状态，可以通过观察脉冲激发态的亚皮秒动力学来揭示。此外，最近的实验和理论发展使得在极端条件下监测单粒子和集体激发的时间演变成为可能，例如由强和选择性光刺激引起的那些。这些发展为新的非平衡现象开辟了道路，这些现象最终可以由短激光脉冲诱发和操纵。在这里，我们回顾了相关材料的非平衡电子、光学、结构和磁性能的实验和理论研究的最新成果。重点将主要放在表现出非常规超导性或其他奇异相的相关氧化物的原型案例上。讨论还将扩展到其他主题系统，例如铁基和有机超导体，以及电荷转移绝缘体。通过这次审查，对新的实验工具和理论方法、模型和概念的需求将明显增长。特别是，扩展实际实验能力以及数值和分析工具以在微观上处理非简单现象学方法之外的非平衡现象的必要性代表了物理学中最具挑战性的新前沿之一。和电荷转移绝缘体。通过这次审查，对新的实验工具和理论方法、模型和概念的需求将明显增长。特别是，扩展实际实验能力以及数值和分析工具以在微观上处理非简单现象学方法之外的非平衡现象的必要性代表了物理学中最具挑战性的新前沿之一。和电荷转移绝缘体。通过这次审查，对新的实验工具和理论方法、模型和概念的需求将明显增长。特别是，扩展实际实验能力以及数值和分析工具以在微观上处理非简单现象学方法之外的非平衡现象的必要性代表了物理学中最具挑战性的新前沿之一。