Extremely wide 13 magnetic plateau of volborthite Cu3V2O7(OH)2·2H2O in ultrahigh magnetic fields up to 182 T

In an attempt to confirm the end of the $\frac{1}{3}$ magnetization plateau of volborthite single crystals, Faraday rotation measurements were taken in magnetic fields up to 182 T at low temperatures. Depending on whether or not the sample setting condition is free-standing, two types of $\frac{1}{3}$ plateaus have been observed: One ends around 100 T with a plateau width about $80--90$ T, and the other continues above 160 T, exhibiting an extremely wide plateau (more than 140 T). These contrasting differences are explained by the way in which the $\frac{1}{3}$-plateau phase changes with or without a lattice distortion associated with the crystal symmetry.