Evidence for a quasi-1D topological-excitation liquid in Bi ₂ Sr ₂ CaCu ₂ O _{8 + x} from tunneling spectroscopy

Abstract

Tunneling measurements have been carried out on heavily underdoped and slightly overdoped Bi2Sr2CaCu2O8+x (Bi2212) single crystals by using a break-junction technique. We find that inplane tunneling spectra below Tc are the combination of incoherent part from the pseudogap and coherent quasiparticle peaks. There is a correlation between the magnitude of the pseudogap and the magnitude of the superconducting gap in Bi2212. We find that the quasiparticle conductance peaks are caused by condensed solitonlike excitations. [7]). In fig. 1(b), one can see that the I(V ) curve at high positive (low negative) bias passes not below (above) the straight dash line [8] but far above (below) the line. This fact cannot be explained by the d-wave symmetry of the order parameter. To our knowledge, this question has never been raised in the literature before. This finding is the main motivation of the present work.To the best of our knowledge, the soliton SC was for the first time considered in ref. [9] in order to explain the SC in organic quasi-one-dimensional (quasi-1D) conductors. Later, Davydov [10,11] applied the model of soliton SC to cuprates. The theory is based on the concept of bisolitons, or electron (or hole) pairs coupled in a singlet state due to local deformation of the lattice.Tunneling spectroscopy is an unique probe of SC state in that it can, in principle, reveal the quasiparticle (QP) excitation density of states (DOS) directly with high energy resolution. In this paper, we present tunneling measurements performed on heavily underdoped and slightly overdoped Bi2212 single crystals by using a break-junction technique. We find that in -plane tunneling spectra below T c are the combination of incoherent part from the PG and coherent QP peaks. There is a correlation between the magnitude of the PG and the magnitude of the SG in Bi2212. We find that the QP conductance peaks are caused by condensed topological solitons. Thus, we present an evidence for a quasi-1D topological-excitation liquid in Bi2212.The overdoped Bi2212 single crystals were grown using a self-flux method as described elsewhere [12]. The underdoped samples were obtained from the overdoped single crystals by annealing them in vacuum. The T c value was determined by the four-contact method. The transition width is less than 1 K in the overdoped crystals, and a few degrees in the underdoped Bi2212.Experimental details of our break-junction setup can be found elsewhere [13]. In short, many break-junctions were prepared by gluing a sample with epoxy on a flexible insulating substrate, and then were broken in the abplane by bending the substrate with a differential screw at low temperature in a He ambient. The electrical con-1

MECHANISM OF HIGH-Tc SUPERCONDUCTIVITY BASED MAINLY ON TUNNELING MEASUREMENTS IN CUPRATES

“…In plots (c)-(e), the current difference is presented in %. 6,7,38,36 in Figs. 17c-17e reach a plateau value.…”

A possible scenario for the mechanism of high-Tc superconductivity based on experimental data

“…Let us start with analysis of experimental data, made earlier in a recent review, a book and a few papers [2][3][4][5][6]. In fact, we need just two conclusions obtained for SC in cuprates [2][3][4][5][6].…”

“…Let us start with analysis of experimental data, made earlier in a recent review, a book and a few papers [2][3][4][5][6]. In fact, we need just two conclusions obtained for SC in cuprates [2][3][4][5][6]. Analysis of tunneling, neutron scattering (INS) and muonspin-relaxation data shows that spin fluctuations mediate the long-range phase coherence in cuprates [2][3][4][5].…”

“…Analysis of tunneling, neutron scattering (INS) and muonspin-relaxation data shows that spin fluctuations mediate the long-range phase coherence in cuprates [2][3][4][5]. At the same time, analysis of tunneling, INS, X-ray scattering and angle-resolved photoemission (ARPES) data indicates that the Cooper pairs in cuprates are most likely topological excitations, and phonons seem to be responsible for the pairng [2][3][4]6]. (For more details, see the references [2][3][4][5][6].…”

“…At the same time, analysis of tunneling, INS, X-ray scattering and angle-resolved photoemission (ARPES) data indicates that the Cooper pairs in cuprates are most likely topological excitations, and phonons seem to be responsible for the pairng [2][3][4]6]. (For more details, see the references [2][3][4][5][6]. )…”