Thursday, June 27, 2013

1306.6306 (T. Wu et al.)

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

T. Wu, H. Mayaffre, S. Krämer, M. Horvatić, C. Berthier, C. T. Lin, D. Haug, T. Loew, V. Hinkov, B. Keimer, M. -H. Julien
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.
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