Single-shot real-time tracking of a light-induced metastable phase transition in an electronic crystal

Metastable hidden phases are long-lived states that are typically inaccessible in equilibrium phase diagrams but can emerge under dynamic stimuli, such as tailored laser excitation. Understanding the evolution of these states is of both fundamental and practical significance, allowing the exploration of nonequilibrium thermodynamics and the development of optoelectronic devices with on-demand photoresponses. However, probing the ultrafast formation of a metastable hidden phase remains a long-standing challenge in physics since the initial state of the system is not recovered rapidly. Here, using a suite of state-of-the-art single-shot spectroscopy techniques, we present a direct ultrafast visualization of the photoinduced phase transition to a metastable hidden state in an electronic crystal, 1T-TaS2. Capturing the dynamics of this complex phase transformation in a single-shot fashion demonstrates a commonality in microscopic pathways that the system undergoes to enter the hidden state and provides unambiguous spectral fingerprints that distinguish such state from thermally accessible phases. Our finding dispels much of the debate surrounding this elusive hidden phase and presents a critical tool for the discovery of new exotic phenomena in quantum materials.