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Magnetic fields can cause the formation of vortices in a superconductor. In cuprate superconductors, the vortex cores are surrounded by “halos,” where the density of electronic states exhibits a checkerboard pattern. Edkins et al. used scanning tunneling spectroscopy to take a closer look into the halos. The results revealed that the patterns correspond to an exotic state called the pair density wave, in which the density of finite momentum Cooper pairs is spatially modulated.Science, this issue p. 976High magnetic fields suppress cuprate superconductivity to reveal an unusual density wave (DW) state coexisting with unexplained quantum oscillations. Although routinely labeled a charge density wave (CDW), this DW state could actually be an electron-pair density wave (PDW). To search for evidence of a field-induced PDW, we visualized modulations in the density of electronic states N(r) within the halo surrounding Bi2Sr2CaCu2O8 vortex cores. We detected numerous phenomena predicted for a field-induced PDW, including two sets of particle-hole symmetric N(r) modulations with wave vectors QP and 2QP, with the latter decaying twice as rapidly from the core as the former. These data imply that the primary field-induced state in underdoped superconducting cuprates is a PDW, with approximately eight CuO2 unit-cell periodicity and coexisting with its secondary CDWs.
