Nuclear magnetic resonance study of charge density waves under hydrostatic pressure in YBa2Cu3Oy

Abstract

The effect of hydrostatic pressure ($P$) on charge density waves (CDWs) in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{\mathrm{y}}$ 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 $\ensuremath{\approx}1$ 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 $\ensuremath{\approx}10$--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 $\ensuremath{\approx}15$ GPa arises from a concomitant decrease of CDW strength.