A four unit cell periodic pattern of quasi-particle states surrounding vortex cores in Bi₂Sr₂CaCu₂O_8+δ

Scanning tunneling microscopy is used to image the additional quasi-particle states generated by quantized vortices in the high critical temperature superconductor Bi₂Sr₂CaCu₂O_8+δ. They exhibit a copper-oxygen bond-oriented "checkerboard" pattern, with four unit cell (4a_o) periodicity and a ∼30 angstrom decay length. These electronic modulations may be related to the magnetic field-induced, 8a_o periodic, spin density modulations with decay length of ∼70 angstroms recently discovered in La_1.84Sr_0.16CuO₄. The proposed explanation is a spin density wave localized surrounding each vortex core. General theoretical principles predict that, in the cuprates, a localized spin modulation of wavelength λ should be associated with a corresponding electronic modulation of wavelength λ/2, in good agreement with our observations.