Direct observation of competition between superconductivity and charge density wave order in YBa2Cu3O6.67

Abstract

X-ray diffraction experiments reveal that spatial charge ordering occurs in the pseudogap state of YBa2Cu3O6.67. Moreover, this charge ordered state competes with high-temperature superconductivity, and their relative strengths can be tuned using a magnetic field. Superconductivity often emerges in the proximity of, or in competition with, symmetry-breaking ground states such as antiferromagnetism or charge density waves1,2,3,4,5 (CDW). A number of materials in the cuprate family, which includes the high transition-temperature (high-Tc) superconductors, show spin and charge density wave order5,6,7. 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 superstructure8. 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 pockets9, which explain the negative Hall and Seebeck effects10,11 and the ‘Tc plateau’12 in this material when underdoped.