Temperature-dependent pseudogap-like features in tunnel spectra of high-T_ccuprates as a manifestation of charge-density waves

Abstract

Temperature, T, variations of the tunnel conductance G(V) were calculated for junctions between a normal metal and a spatially inhomogeneous superconductor with a dielectric gap on the nested sections of the Fermi surface or between two such superconductors. The dielectric gapping was considered to be a consequence of the charge density wave (CDW) appearance due to the electron–phonon (for a Peierls insulator) or a Coulomb (for an excitonic insulator) interactions. Spatial averaging was carried out over random domains with varying parameters of the CDW superconductor (CDWS). The calculated tunnel spectra demonstrate a smooth transformation from asymmetric patterns with a pronounced dip–hump structure at low T into those with a pseudogap depletion of the electron densities of states at higher T in the vicinity or above the actual critical temperatures of the superconducting transition for any of the CDWS domains. Thus, it is demonstrated that both the dip-hump structure and pseudogapping are manifestations of the same phenomenon. A possible CDW-induced asymmetry of the background contribution to G(V) is also touched upon. The results explain the peculiar features of G(V) for Bi2Sr2CaCu2O8+δ and other related high-Tc cuprates.

Competition of Superconductivity and Charge Density Waves in Cuprates: Recent Evidence and Interpretation

“…In this connection, the failure of the most sophisticated approaches to make any prediction of true or, at least "bare" T c , (provided that the corresponding T c -value is not known a priori) despite hundreds of existing superconductors with varying fascinating properties, forced Phillips [63] to reject all apparently first-principle continuum theories in favor of his own percolative filamentary theory of superconductivity [64][65][66][67] (see also the random attractive Hubbard model studies of superconductivity [68,69] and the analysis of competition between superconductivity and charge density waves studied in the framework of similar scenarios [70][71][72]). We totally agree with such considerations in the sense of the important role of disorder in superconductors with high T c on the verge of crystal lattice instability [73][74][75][76][77][78][79][80][81][82][83]. Nevertheless, it is questionable whether a simple one-parameter "master function" of [63,67] would be able to make quantitative and practically precise predictions of T c .…”

Hard-Wired Dopant Networks and the Prediction of High Transition Temperatures in Ceramic Superconductors

“…The combination of electron-phonon interactions and ionicity readily explains [79] how superconductivity in the covalent (noncentral interatomic forces) FeAs family can be much more isotropic than in the cuprates [80], yet still retain a lowered dimensionality. Strong disorder explains "hump-dip" pseudogap tunneling features in terms of charge density waves [81].…”

Spatial distribution of superconducting and charge-density-wave order parameters in cuprates and its influence on the quasiparticle tunnel current (Review Article)

“…The formulas for the current ( ) J V through the junction concerned were obtained in the tunnel-Hamiltonian approach [14,57,[99][100][101][102][103] ( )…”