Press Releases

2016.05.30

Bipartite electronic superstructures in the vortex core of Bi2Sr2CaCu2O8+δ : Associate Professor Tsuyoshi Tamegai, Department of Applied Physics, and other researchers.

The central issue in the physics of cuprate superconductivity is the mutual relationship among superconductivity, pseudogap and broken-spatial-symmetry states. A magnetic field B suppresses superconductivity, providing an opportunity to investigate the competition among these states. Although various B-induced electronic superstructures have been reported, their energy, spatial and momentum-space structures are unclear. Here, we show using spectroscopic-imaging scanning tunnelling microscopy on Bi2Sr2CaCu2O8+δ that there are two distinct B-induced electronic superstructures, both being localized in the vortex core but appearing at different energies. In the low-energy range where the nodal Bogoliubov quasiparticles are well-defined, we observe the so-called vortex checkerboard that we identify as the B-enhanced quasiparticle interference pattern. By contrast, in the high-energy region where the pseudogap develops, the broken-spatial-symmetry patterns that pre-exist at B=0T is locally enhanced in the vortex core. This evidences the competition between superconductivity and the broken-spatial-symmetry state that is associated with the pseudogap.

 

(a,b) Differential conductance maps at energy E=+10 meV in magnetic fields B=0 and 11 T, respectively. White arrows in a denote the Cu–O bonding directions. Vortices and their internal structures (vortex checkerboard) are clearly imaged in b. (c,d) Differential conductance maps at E=−10 meV taken in B=0 and 11 T. Scale bars, 50 Å (a–d), and the colour scales are in nano siemens (nS). The tunnelling conductance at each location was obtained by numerical differentiation of the current–voltage characteristics and by post-smoothing with the energy window of ±2 meV. (e) Comparison between tunnelling spectra taken at B=0 T (open symbols) and 11 T (solid symbols). Red and blue data depict the spectra spatially averaged over the regions near vortices and far from vortices, respectively. (f) Schematic illustration of the excitation gap in momentum-space showing the dichotomy between the d-wave superconductivity near the node (light blue area) and the antinodal states governed by the pseudogap (yellow area). These two regimes are separated by the line connecting (π/a0, 0) and (0, π/a0), where a0 denotes Cu–O–Cu distance.

 

Abstract URL: http://www.nature.com/ncomms/2016/160527/ncomms11747/full/ncomms11747.html