Charge order and superconductivity in underdoped YBa₂Cu₃O_7-δ under pressure

In underdoped cuprates, an incommensurate charge density wave (CDW) order is known to coexist with superconductivity. A dip in Tc at the hole doping level where the CDW is strongest (np≃0.12) suggests that CDW order may suppress superconductivity. We investigate the interplay of charge order with superconductivity in underdoped YBa2Cu3O7-δ by measuring the temperature dependence of the Hall coefficient RH(T) at high magnetic field and at high hydrostatic pressure. We find that, although pressure increases Tc by up to 10 K at 2.6 GPa, it has very little effect on RH(T). This suggests that pressure, at these levels, only weakly affects the CDW and that the increase in Tc with pressure cannot be attributed to a suppression of the CDW. We argue, therefore, that the dip in Tc at np≃0.12 at ambient pressure is probably not caused by the CDW formation.