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

Abstract

A central question in the underdoped cuprates pertains to the nature of the pseudogap ground state. A conventional metallic ground state of the pseudogap region has been argued to host quantum oscillations upon destruction of the superconducting order parameter by modest magnetic fields. Here, we use low applied measurement currents and millikelvin temperatures on ultrapure single crystals of underdoped YBa2Cu3O6+x to unearth an unconventional quantum vortex matter ground state characterized by vanishing electrical resistivity, magnetic hysteresis, and nonohmic electrical transport characteristics beyond the highest laboratory-accessible static fields. A model of the pseudogap ground state is now required to explain quantum oscillations that are hosted by the bulk quantum vortex matter state without experiencing sizable additional damping in the presence of a large maximum superconducting gap; possibilities include a pair density wave.

Anomalous vortex liquid in charge-ordered cuprate superconductors

“…4E , which illustrates the same qualitative behavior observed in the three long-range charge-ordered cuprates investigated here. The presence of long-range charge order (25)(26)(27)(28)(29)(30) within the vortex solid regime at T 10 K appears to suppress the critical current, leading to a dynamic vortex-solid boundary with respect to the driving current, in accordance with previous magnetic torque and transport experiments (19,20,21). While the upper field limit to which the nonohmic behavior persists is unclear from the present study, our results reveal the existence of an anomalous vortex liquid above µ0Hr at the lowest accessible temperatures, where thermal fluctuations are expected to be negligible and vortices are likely to be depinned by quantum fluctuations intensified by high magnetic fields.…”

“…2C ), the pronounced nonohmic behavior at T 1.2 K, extending up to 45 T, indicates that the resistive state is not a conventional metallic ground state but rather a dissipative vortex liquid (37). The extent of the second vortex solid regime (i.e., the intervening regime in which µ0Hr increases with decreasing I ) is smaller than that observed in Y123 at p = 0.11 (20,21), possibly reflecting the improved stoichiometry in Y124 and/or the weaker strength of the charge order (14,23).…”

“…Recently, a signature of bulk superconductivity has been observed in Y123 at p ≈ 0.11 up to 45 T, namely a small yet finite magnetic hysteresis induced by vortex pinning (19,20) and a zero-resistivity state when a vanishingly small excitation current is used (21). These results suggest the existence of a second vortex-solid regime that is highly susceptible to external perturbations with a markedly reduced critical current density jc in the T → 0 limit.…”

Fragile superconductivity at high magnetic fields

“…Only in certain cuprates does this charge density state exhibit long-range order. However, for the cuprate studied by Hsu et al (2), although only short-range order exists at low magnetic fields, long-range order is established at around 15 tesla (7).…”

“…Tens of thousands of papers have been written on these cuprate materials, yet 35 years later, they continue to surprise us. In PNAS, Hsu et al (2) demonstrate that a fragile form of superconductivity persists in a cuprate up to the highest magnetic field they can muster.…”