Chang, J.2; Blackburn, E.3; Holmes, A. T.3; Christensen, N. B.1; Larsen, Jacob4; Mesot, J.2; Liang, Ruixing5; Bonn, D. A.5; Hardy, W. N.5; Watenphul, A.6; Zimmermann, M. v.6; Forgan, E. M.3; Hayden, S. M.7
1 Department of Physics, Technical University of Denmark2 École Polytechnique Fédérale de Lausanne3 University of Birmingham4 Experimental Surface and Nanomaterials Physics, Department of Physics, Technical University of Denmark5 University of British Columbia6 Deutsches Elektronen-Synchrotron7 University of Bristol
Superconductivity often emerges in the proximity of, or in competition with, symmetry-breaking ground states such as antiferromagnetism or charge density waves (CDW). A number of materials in the cuprate family, which includes the high transition-temperature (high-Tc) superconductors, show spin and charge density wave order. Thus a fundamental question is to what extent do these ordered states exist for compositions close to optimal for superconductivity. Here we use high-energy X-ray diffraction to show that a CDW develops at zero field in the normal state of superconducting YBa2Cu3O6.67 (Tc= 67 K). This sample has a hole doping of 0.12 per copper and a well-ordered oxygen chain superstructure. Below Tc, the application of a magnetic field suppresses superconductivity and enhances the CDW. Hence, the CDW and superconductivity in this typical high-Tc material are competing orders with similar energy scales, and the high-Tc superconductivity forms from a pre-existing CDW environment. Our results provide a mechanism for the formation of small Fermi surface pockets, which explain the negative Hall and Seebeck effects and the ‘Tc plateau’ in this material when underdoped.