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

Abstract

Explicit and implicit experimental evidence for charge density wave (CDW) presence in high-Tcsuperconducting oxides is analyzed. The theory of CDW superconductors is presented. It is shown that the observed pseudogaps and dip-hump structures in tunnel and photoemission spectra are manifestations of the same CDW gapping of the quasiparticle density of states. Huge pseudogaps are transformed into modest dip-hump structures at low temperatures,T, when the electron spectrum superconducting gapping dominates. Heat capacity jumps at the superconducting critical temperature and the paramagnetic limit are calculated for CDW superconductors. For a certain range of parameters, the CDW state in ad-wave superconductor becomes reentrant withT, the main control quantity being a portion of dielectrcally gapped Fermi surface. It is shown that in the weak-coupling approximation, the ratio between the superconducting gap at zero temperatureΔ(T=0)andTchas the Bardeen-Cooper-Schrieffer value fors-wave Cooper pairing and exceeds the corresponding value ford-wave pairing of CDW superconductors. Thus, large experimentally found values2Δ(T=0)/Tc≈5÷8are easily reproduced with reasonable input parameter values of the model. The conclusion is made that CDWs play a significant role in cuprate superconductivity.