A Four Unit Cell Periodic Pattern of Quasi-Particle States Surrounding Vortex Cores in Bi ₂ Sr ₂ CaCu ₂ O 8+δ

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Scanning tunneling microscopy is used to image the additional quasi-particle states generated by quantized vortices in the high critical temperature superconductor Bi 2 Sr 2 CaCu 2 O 8+δ . They exhibit a copper-oxygen bond–oriented “checkerboard” pattern, with four unit cell (4 a 0 ) periodicity and a ∼30 angstrom decay length. These electronic modulations may be related to the magnetic field–induced, 8 a 0 periodic, spin density modulations with decay length of ∼70 angstroms recently discovered in La 1.84 Sr 0.16 CuO 4 . 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.