Electronic charges introduced in copper-oxide (CuO 2 ) planes generate hightransition temperature (T c ) superconductivity but, under special circumstances, they can also order into filaments called stripes (1). Whether an underlying tendency of charges to order is present in all cuprates and whether this has any relationship with superconductivity are, however, two highly controversial issues (2,3). In order to uncover underlying electronic orders, magnetic fields strong enough to destabilise superconductivity can be used. Such experiments, including quantum oscillations (4-6) in YBa 2 Cu 3 O y (a notoriously clean cuprate where charge order is not observed) have suggested that superconductivity competes with spin, rather than charge, order (7-9). Here, using nuclear magnetic resonance, we demonstrate that high magnetic fields actually induce charge order, without spin order, in the CuO 2 planes of YBa 2 Cu 3 O y . The observed static, unidirectional, modulation of the charge density breaks translational symmetry, thus explaining quantum oscillation results, and we argue that it is most likely the same 4a- The ortho II structure of YBa 2 Cu 3 O 6.54 (p=0.108) leads to two distinct planar Cu NMR sites: Cu2F are those Cu located below oxygen-filled chains and Cu2E those below oxygen-empty chains (10). The main discovery of our work is that, on cooling in a field H 0 of 28.5 T along the c axis (i.e. in the conditions for which quantum oscillations are resolved; See supplementary materials), the Cu2F lines undergo a profound change while the Cu2E lines do not (Fig. 1). To first order, this change can be described as a splitting of Cu2F into two sites having both different hyperfine shifts K=/H 0 ( is the hyperfine field due to electronic spins) and quadrupole frequencies ν Q (Related to the electric field gradient). Additional effects might be present ( Fig. 1), but they are minor compared to the observed splitting. Field and temperature dependent orbital occupancy (e.g. d x 2 -y 2 vs. d z 2 -r 2 ) changes without on-site electronic density change are implausible and any out-of-plane charge-density or lattice change would affect Cu2E sites as well. Thus, the change of ν Q can only arise from a differentiation in the charge density among Cu2F sites (or at the oxygen sites bridging them). A change in the asymmetry parameter and/or in the direction of the principal axis of the electric field gradient could also be associated with this charge differentiation, but these are relatively small effects.Remarkably, the charge differentiation occurs below T charge =50±10 K for p=0.108 whatever the precise profile of the static charge modulation is, the reconstruction must be related to the translational symmetry breaking by the charge ordered state.The absence of any splitting or broadening of Cu2E lines implies a onedimensional character of the modulation within the planes and imposes strong constraints on the charge pattern. Actually, only two types of modulations are compatible with a Cu2F splitting (Fig. 2). T...

The pseudogap regime of high-temperature cuprates harbours diverse manifestations of electronic ordering whose exact nature and universality remain debated. Here, we show that the short-ranged charge order recently reported in the normal state of YBa2Cu3Oy corresponds to a truly static modulation of the charge density. We also show that this modulation impacts on most electronic properties, that it appears jointly with intra-unit-cell nematic, but not magnetic, order, and that it exhibits differences with the charge density wave observed at lower temperatures in high magnetic fields. These observations prove mostly universal, they place new constraints on the origin of the charge density wave and they reveal that the charge modulation is pinned by native defects. Similarities with results in layered metals such as NbSe2, in which defects nucleate halos of incipient charge density wave at temperatures above the ordering transition, raise the possibility that order–parameter fluctuations, but no static order, would be observed in the normal state of most cuprates if disorder were absent.