Magnetic field-enhanced spin freezing in YBa2Cu3O6.45 at the verge of the competition between superconductivity and charge order

TL;DR

This study uses 63Cu NMR to show that magnetic fields enhance spin order in YBa2Cu3O6.45 due to competition with superconductivity, revealing a universal behavior in underdoped cuprates linked to charge order.

Contribution

It demonstrates that magnetic field-induced spin freezing in YBa2Cu3O6.45 is due to competition with superconductivity and is similar to phenomena observed in other cuprates, suggesting a universal mechanism.

Findings

Magnetic field enhances spin order only when perpendicular to CuO2 planes.

Spin-freezing has a glassy nature and occurs at a temperature independent of field strength.

Results indicate a universal interplay between spin order, charge order, and superconductivity in underdoped cuprates.

Abstract

Using 63Cu NMR, we establish that the enhancement of spin order by a magnetic field H in YBa2Cu3O6.45 arises from a competition with superconductivity because the effect occurs for H perpendicular, but not parallel, to the CuO2 planes, and it persists up to field values comparable to Hc2. We also find that the spin-freezing has a glassy nature and that the frozen state onsets at a temperature which is independent of the magnitude of H. These results, together with the presence of a competing charge-ordering instability at nearby doping levels, are strikingly parallel to those previously obtained in La-214. This suggests a universal interpretation of magnetic field effects in underdoped cuprates where the enhancement of spin order by the field may not be the primary phenomenon but rather a byproduct of the competition between superconductivity and charge order. Low-energy spin fluctuations are manifested up to relatively high temperatures where they partially mask the signature of the pseudogap in 1/T1 data of planar Cu sites.