Unconventional quantum vortex matter state hosts quantum oscillations in the underdoped high-temperature cuprate superconductors

A central question in the underdoped cuprates pertains to thenature of the pseudogap ground state. A conventional metallicground state of the pseudogap region has been argued to hostquantum oscillations upon destruction of the superconductingorder parameter by modest magnetic fields. Here, we use lowapplied measurement currents and millikelvin temperatures onultrapure single crystals of underdoped YBa2Cu3O6+xto unearthan unconventional quantum vortex matter ground state char-acterized by vanishing electrical resistivity, magnetic hysteresis,and nonohmic electrical transport characteristics beyond the high-est laboratory-accessible static fields. A model of the pseudogapground state is now required to explain quantum oscillationsthat are hosted by the bulk quantum vortex matter state with-out experiencing sizable additional damping in the presence of alarge maximum superconducting gap; possibilities include a pairdensity wave