The Importance of Topological Defects in Photoexcited Phase Transitions Including Memory Applications

Photoinduced phase transitions have become a very important field of study with the advent of diverse time-resolved experimental techniques whose time resolution matches the electron, lattice, and spin relaxation dynamics associated with elementary excitations in quantum materials. Most techniques currently available rely on stroboscopic data-averaging over multiple transition outcomes. However, each time a transition takes place, fluctuations close to the time of the transition ensure that the phase transition outcome is different, with the emergence of different topological defect textures. In this paper, we briefly review the non-perturbative processes in selected charge-ordered quantum systems and the methods for their observation with different time-resolved techniques and scanning tunneling microscopy, which avoids the problem of averaging. The topological defect dynamics are seen to play an essential role in stabilizing emergent states in non-equilibrium transitions, appearing on different timescales as well as determining the emergent properties of the system. The phenomena are fundamentally important for understanding the fabric of matter in the Universe, as well as for possible applications in non-volatile memory devices.