Deviation from Canonical Collective Creep Behavior in Li0.8Fe0.2OHFeSe

We present an extensive study of the vortex dynamics in Li0.8Fe0.2OHFeSe single crystal, which is prepared by intercalating insulating spacer layer Li0.8Fe0.2OHFeSe into FeSe. Absence of fishtail effect and the crossover from elastic to plastic creep are observed similar to the parent compound FeSe. However, when we apply collective creep theory to the magnetic relaxation data, the obtained creep exponent mu is found to be similar to 4.1 much larger than the predicted maximum value. Besides, the elastic creep in the vortex phase diagram of Li0.8Fe0.2OHFeSe is found to reside only in an extremely small region. Such a large value of mu and the small elastic creep region may be originated from the weakening of coupling between the vortices in neighboring layers by elongating the layer distance. It may indicate that the vortex structure of Li0.8Fe0.2OHFeSe is in the crossover regime between elastic Abrikosov vortices to stacks of pancake vortices. Our study also suggests that the intercalated FeSe is a promising candidate for searching intrinsic Josephson phenomena.