A Four Unit Cell Periodic Pattern of Quasi-Particle States Surrounding Vortex Cores in

Scanning tunneling microscopy is used to image the additional quasi-particle states generated by quantized vortices in the high critical temperature superconductor Bi2Sr2CaCu2O81d. They exhibit a copper-oxygen bond— oriented “checkerboard” pattern, with four unit cell (4a 0 ) periodicity and a ;30 angstrom decay length. These electronic modulations may be related to the magnetic field—induced, 8a 0 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 l should be associated with a corresponding electronic modulation of wavelength l/2, in good agreement with our observations.