Quasi-one-dimensional topological-excitationliquid in Bi2Sr2CaCu2O8+x from tunnellingspectroscopy

Abstract

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 thatin-plane tunnelling spectra below Tc are a combination of the incoherentpart from the pseudogap and coherent quasiparticle peaks. There is a clearcorrelation between the magnitude of the pseudogap and the magnitude of thesuperconducting gap in Bi2212. Analysis of the data suggests that the tunnelling pseudogap in Bi2212 is predominantly a charge-density-wave gapon dynamical charge stripes. The tunnelling characteristics corresponding tothe quasiparticle peaks are in excellent agreement with theoreticalpredictions made for a quasi-one-dimensional topological-excitation liquid. Inaddition, analysis of the data measured by different techniques shows that thephase coherence along the c-axis is established at Tc due to spinfluctuations in local antiferromagnetic domains of CuO2 planes.