M. Kang,1 J. Pelliciari,1 Y. Krockenberger,2 J. Li,1 D. E. McNally,3 E. Paris,3 R. Liang,4,5 W. N. Hardy,4,5 D. A. Bonn,4,5 H. Yamamoto,2 T. Schmitt,3 and R. Comin1,* 1Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA 2NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan 3Research Department Synchrotron Radiation and Nanotechnology, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland 4Department of Physics and Astronomy, University of British Columbia V6T 1Z1, Canada 5Quantum Matter Institute, University of British Columbia V6T 1Z4, Canada

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.

This work is supported by the US Department of Energy BES \Science at 100 T," the National Science Foundation, the State of Florida, the Natural Science and Engineering Research Council of Canada and the Canadian Institute for Advanced Research. S.E.S. ac- knowledges support from the Royal Society and the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013) / ERC Grant Agree- ment no. 337425.

Magnetic images of two sparsely twinned YBa2Cu3O7-delta single crystals were taken in low applied magnetic fields (H-a < 100 mG) with a scanning SQUID microscope. The SQUID sensors have 4 or 8 mu m pickup loops and a magnetic flux resolution of 10(-3)hc/2e under normal operating conditions. The images showed Meissner screening with a large demagnetization factor and isolated trapped vortices. The trapped vortices carried integral (hc/2e) magnetic flux and were much smaller than the spatial resolution of the sensor. At this level of resolution, there was no evidence for unusual magnetic features, such as fractional vortices, associated with the twin boundaries.

We have observed, by 2D positron annihilation, the rigid-shaped Fermi surface related to the chains in the compound series (R)Ba2Cu3O7-delta for R = Y, Dy, Ho, and Pr. In the case of Y we have sighted the clear signature of the ridge in the fourth Brillouin zone and have observed the effect of substituting Cu with Ni, Zn, and Al. The presence of the ridge is also seen in PrBa2Cu3O7-delta which has an insulating character. This shows that chains have a Fermi surface but contribute little to conductivity. This observation is discussed in view of the above alloying experiments, and in view of the recent model of Fehren-bacher and Rice.