Ravnik Jan, Diego Michele, Gerasimenko Yaroslav, Vaskivskyi Yevhenii, Vaskivskyi Igor, Mertelj Tomaz, Vodeb Jaka, Mihailovic Dragan
Complex Matter Department, Jozef Stefan Institute, Ljubljana, Slovenia.
Laboratory for Micro and Nanotechnology, Paul Scherrer Institut, Villigen PSI, Switzerland.
Nat Commun. 2021 Apr 19;12(1):2323. doi: 10.1038/s41467-021-22646-7.
Metastable self-organized electronic states in quantum materials are of fundamental importance, displaying emergent dynamical properties that may be used in new generations of sensors and memory devices. Such states are typically formed through phase transitions under non-equilibrium conditions and the final state is reached through processes that span a large range of timescales. Conventionally, phase diagrams of materials are thought of as static, without temporal evolution. However, many functional properties of materials arise as a result of complex temporal changes in the material occurring on different timescales. Hitherto, such properties were not considered within the context of a temporally-evolving phase diagram, even though, under non-equilibrium conditions, different phases typically evolve on different timescales. Here, by using time-resolved optical techniques and femtosecond-pulse-excited scanning tunneling microscopy (STM), we track the evolution of the metastable states in a material that has been of wide recent interest, the quasi-two-dimensional dichalcogenide 1T-TaS. We map out its temporal phase diagram using the photon density and temperature as control parameters on timescales ranging from 10 to 10 s. The introduction of a time-domain axis in the phase diagram enables us to follow the evolution of metastable emergent states created by different phase transition mechanisms on different timescales, thus enabling comparison with theoretical predictions of the phase diagram, and opening the way to understanding of the complex ordering processes in metastable materials.
量子材料中的亚稳态自组织电子态至关重要，展现出可用于新一代传感器和存储设备的新兴动力学特性。此类状态通常通过非平衡条件下的相变形成，最终状态通过跨越很大时间尺度范围的过程达到。传统上，材料的相图被认为是静态的，没有时间演化。然而，材料的许多功能特性是由于材料在不同时间尺度上发生的复杂时间变化而产生的。迄今为止，即使在非平衡条件下不同相通常在不同时间尺度上演化，此类特性也未在随时间演化的相图背景下被考虑。在此，通过使用时间分辨光学技术和飞秒脉冲激发扫描隧道显微镜（STM），我们追踪了一种近期备受关注的材料——准二维二硫属化物1T-TaS中 metastable 态的演化。我们以光子密度和温度作为控制参数，在10到10秒的时间尺度上绘制出其时间相图。在相图中引入时域轴使我们能够追踪由不同相变机制在不同时间尺度上产生的亚稳态新兴态的演化，从而能够与相图的理论预测进行比较，并为理解亚稳材料中的复杂有序过程开辟道路。
