Theory of Superconductivity (Perseus Books, Reading, 1964). Charge- and spin-density waves in existing superconductors: Competition between Cooper pairing and Peierls or excitonic instabilities. Density Waves in Solids (Addison-Wesley, Massachusetts, 1994). Our results demonstrate that charge order can boost superconductivity in an electron–phonon coupled system, in direct contrast to the prevailing view that it only competes with superconductivity. These k points also show the highest electron–phonon coupling and lowest Fermi velocities. Temperature-dependent angle-resolved photoemission spectroscopy of 2H-NbSe 2 across the CDW and superconducting transitions ( T CDW ∼33 K and T c=7.2 K, respectively) shows CDW-induced spectral-weight depletion at the same Fermi-surface-crossing k points, which evolve into the largest superconducting gaps. Here we provide evidence for maximized superconductivity at points in momentum ( k) space that are directly connected by the CDW ordering vector.
Consequently, these two ground states are believed to compete with each other. Although both conventional charge-density-wave (CDW) and superconducting transitions show an energy gap in the single-particle density of states at the Fermi level ( E F), their physical properties are poles apart: insulating behaviour for the CDW and zero resistivity in superconductors.
Charge ordering and superconductivity are observed in the phase diagrams of a variety of materials such as NbSe 3, layered transition-metal dichalcogenides and high-temperature copper oxide superconductors, low-dimensional organics, Ba 1− xK xBiO 3 and so forth.