Nuclear magnetic resonance study of charge density waves under hydrostatic pressure in YBa2Cu3O3

The effect of hydrostatic pressure (P) on charge density waves (CDWs) in YBa2Cu3Oy has recently been controversial. Using NMR, we find that both the short-range CDW in the normal state and the long-range CDW in high fields are, at most, slightly weakened at P = 1.9 GPa. This result is in contradiction with x-ray-scattering results finding complete suppression of the CDW at approximate to 1 GPa and we discuss possible explanations of this discrepancy. Quantitative analysis, however, shows that the NMR data are not inconsistent with a disappearance of the CDW on a larger pressure scale, typically approximate to 10-20 GPa. We also propose a simple model reconciling transport data with such a hypothesis, provided the pressure-induced change in doping is taken into account. We conclude that it is therefore possible that most of the spectacular increase in T-c upon increasing pressure up to approximate to 15 GPa arises from a concomitant decrease of CDW strength.