Scanning tunneling microscopy is used to image the additional quasi-particle states generated by quantized vortices in the high critical temperature superconductor Bi2Sr2CaCu2O8+δ. They exhibit a copper-oxygen bond-oriented "checkerboard" pattern, with four unit cell (4ao) periodicity and a ∼30 angstrom decay length. These electronic modulations may be related to the magnetic field-induced, 8ao periodic, spin density modulations with decay length of ∼70 angstroms recently discovered in La1.84Sr0.16CuO4. 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.
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