A Four-Unit-Cell Periodic Pattern of Quasiparticle States Surrounding   Vortex Cores in Bi2Sr2CaCu2O8+d
  Scanning tunneling microscopy is used to image the additional quasiparticle states generated by quantized vortices in the high-Tc superconductor Bi2Sr2CaCu2O8+d. They exhibit a Cu-O bond oriented 'checkerboard' pattern, with four unit cell (4a0) periodicity and a ~30 angstrom decay length. These electronic modulations may be related to the magnetic field-induced, 8a0 periodic, spin density modulations of decay length ~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. 
J. E. Hoffman (1), E. W. Hudson (1,2), K. M. Lang (1), V. Madhavan   (1), H. Eisaki (3), S. Uchida (3) & J.C. Davis (1,2) ((...