Quasi-one-dimensional topological-excitation liquid in Bi2Sr2CaCu2O8+x from tunnelling spectroscopy

Tunnelling measurements have been carried out on heavily underdoped, slightly overdoped and partially Ni-substituted Bi2Sr2CaCu2O8+x (Bi2212) single crystals by using a break-junction technique. We: find that in-plane tunnelling spectra below T-c are a combination of the incoherent part from the pseudogap and coherent quasiparticle peaks. There is a clear correlation between the magnitude of the pseudogap and the magnitude of the superconducting gap in Bi2212. Analysis of the data suggests that the tunnelling pseudogap in Bi2212 is predominantly a charge-density-wave gap on dynamical charge stripes. The tunnelling characteristics corresponding to the quasiparticle peaks are in excellent agreement with theoretical predictions made for a quasi-one-dimensional topological-excitation liquid. In addition, analysis of the data measured by different techniques shows that the phase coherence along the c-axis is established at T-c due to spin fluctuations in local antiferromagnetic domains of CuO2 planes.