STM/STS studies on vortex-lattice and antiferromagnetism under high magnetic fields in high-Tc cuprates

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Recently, it has been reported in neutron scattering experiments on La214 high-Tc cuprate that an antiferromagnetic order is induced by the application of magnetic fields in the superconducting state and coexists with the superconductivity. In STM/STS experiments on Bi2212 high-Tc cuprate, it has also been reported that the electronic energy spectrum in vortex cores exhibits the so-called "pseudogap", which is a characteristic feature for the normal state above Tc. In addition, STM/STS experiments on Bi2212 suggested that an electronic charge order with a periodicity of 〜4a×4a develops around vortex cores ; the charge order will be related with the field-induced antiferromagnetic order. In this research project, we have studied the 〜4a×4a charge order by STM/STS on Bi2212, in order to obtain clues to the understanding of the field-induced antiferromagnetic order, the pseudogap and the superconducting mechanism.1. There exist two kinds of Bi2212 samples which exhibit strong and weak 〜4a×4a charge orders in the pseudogap state.2. The pseudogap size is more spatially-inhomogeneous in the Bi2212 sample which exhibits a stronger 〜4a×4a charge order.The latter result seems to indicate that the electronic charge order in the pseudogap state will be dynamically fluctuated in itself ; when there exist a lot of scattering centers causing the spatial inhomogeneity of electronic states, they will act as pinning potentials for the dynamically-fluctuated charge order and make it static.