| In order to understand the origin of superconductivity, it is crucial to ascertain the nature and origin of primary carriers available to participate in pairing1-6. Recent quantum oscillation experiments on high Tc cuprate superconductors7-10 have revealed the existence of a Fermi surface akin to normal metals, comprising fermionic carriers that undergo orbital quantization11. However, the unexpectedly small size of the observed carrier pocket leaves open a variety of possibilities as to the existence or form of any underlying magnetic order, and its relation to d-wave superconductivity12-15. Here we present quantum oscillations in the magnetisation (the de Haas-van Alphen effect) observed in superconducting YBa2Cu3O6.51 that reveal more than one carrier pocket. In particular, we find evidence for the existence of a much larger pocket of heavier mass carriers playing a thermodynamically dominant role in this hole-doped superconductor. Importantly, characteristics of the multiple pockets within this more complete Fermi surface impose constraints on the ordering wavevector of any underlying order and the location of the carriers in momentum space. These constraints enable us to construct a possible spiral density-wave ordering scenario, or related modulated magntic order, consistent with experimental observations. |
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