Inducing Superconductivity by a Picosecond Pressure Transient in the Quasi-Two-Dimensional Organic Salt

自从近100年前发现超导性以来，无数的研究集中在这一现象的起源和驱动机制上。特别是高温（高tc）超导体的发展在过去引起了很大的关注，例如，发现室温超导体将彻底改变电子工程。然而，尽管有这些努力，非常规超导的基本过程仍然不为人所知。高温超导的原型材料是BEDT-TTF族的准二维有机化合物。特别是，κ-(BEDT-TTF)2Cu[N(CN)2]Cl在13k以下表现出非常丰富的相图，包括压力驱动的反铁磁绝缘到超导（AF-SC）相变。到目前为止，所有关于有机超导体的研究都集中在这些材料的平衡特性上，即系统对环境缓慢绝热变化的响应。相比之下，本文的目的是研究利用飞秒激光脉冲激发皮秒压力瞬态（声波）后超导相的动态形成。照射沉积在有机化合物顶部的缓冲层，在材料中发射声脉冲。该压力瞬态以声速穿过样品，并有望诱导AF-SC相变。利用这种方法，超导相的产生可以在时域中直接观察到，而且，方向选择实验可以深入了解反铁磁波动对超导性的作用。

Since the discovery of superconductivity almost 100 years ago, countless studies focused on the origin and driving mechanisms of this phenomenon. In particular the development of high-temperature (high-Tc) superconductors has reached much attention in the past, as the finding of a room-temperature superconductor would, for example, revolutionize electronic engineering. However, despite these efforts, the fundamental processes of unconventional superconductivity are still not understood.Prototype materials for high-Tc superconductivity are the quasi-two-dimensional organic compounds of the BEDT-TTF family. In particular, the κ-(BEDT-TTF)2Cu[N(CN)2]Cl exhibits a very rich phase diagram including a pressure-driven antiferromagnetic insulating-to-superconducting (AF-SC) phase transition below 13 K. So far, all studies of organic superconductors focused on the equilibrium properties of these materials, i.e. the system's response to slow adiabatic changes of the environment. In contrast, the proposed work aims at the investigation of the dynamic formation of the superconducting phase after excitation of a picosecond pressure transient (sound wave) using femtosecond laser pulses. Irradiation of a buffer layer deposited on top of the organic compound launches an acoustic pulse in the material. This pressure transient traverses through the sample at the speed of sound and is expected to induce the AF-SC phase transition. Using this approach, the generation of the superconducting phase could be observed directly in the time domain, and, furthermore, the direction-selective experiment may yield insight into the role of antiferromagnetic fluctuations for superconductivity.