Fourfold structure of vortex-core states in Bi2Sr2CaCu2O8+delta

We present a detailed study of vortex-core spectroscopy in slightly overdoped Bi2Sr2CaCu2O8+delta using a low-temperature scanning tunneling microscope. Inside the vortex core, we observe a fourfold symmetric modulation of the local density of states with an energy-independent period of (4.3 +/- 0.3)a0. Furthermore, we demonstrate that this square modulation is related to the vortex-core states which are located at +/-6 meV. Since the core-state energy is proportional to the superconducting gap magnitude , our results strongly suggest the existence of a direct relation between the superconducting state and the local electronic modulations in the vortex core.     

Dynamic order-to-metastable-disorder vortex matter transition in Bi2Sr2CaCu2O8+delta

Magneto-optical measurements of transient vortex states in Bi2Sr2CaCu2O8+delta show enhanced effects of metastability in prism-shaped as compared to platelet crystals including a significant shift of the second magnetization peak and qualitatively different dynamics. In contrast to platelets, where dislocations are generated only at the sample edges, we propose that in prism samples the dislocations are generated dynamically in the entire sample due to distributed surface barriers. As a result, a dynamic phase transition from a Bragg glass to a metastable disordered phase may occur well below the thermodynamic transition field.