Abstract
Planar oxygen nuclear magnetic resonance (NMR) relaxation and shift data from all cuprate superconductors available in the literature are analyzed. They reveal a temperature-independent pseudogap at the Fermi surface, which increases with decreasing doping in family-specific ways, i.e., for some materials, the pseudogap is substantial at optimal doping while for others it is nearly closed at optimal doping. The states above the pseudogap, or in its absence are similar for all cuprates and doping levels, and Fermi liquid-like. If the pseudogap is assumed exponential it can be as large as about 1500 K for the most underdoped systems, relating it to the exchange coupling. The pseudogap can vary substantially throughout a material, being the cause of cuprate inhomogeneity in terms of charge and spin, so consequences for the NMR analyses are discussed. This pseudogap appears to be in agreement with the specific heat data measured for the YBaCuO family of materials, long ago. Nuclear relaxation and shift show deviations from this scenario near Tc, possibly due to other in-gap states.
Highlights
Nuclear magnetic resonance (NMR) provides important local information about the electronic properties of materials [1], and it has played a key role in the characterization of cuprate high-temperature superconductors [2,3]
The high density of states near the Fermi surface leads to the distinctive, fast nuclear relaxation (1/T1) that is proportional to temperature (1/T1 ∝ T) since temperature increases the available number of electronic states for scattering with nuclear spins
Planar O relaxation and spin shift data were collected and simple plots reveal that they demand a temperature-independent pseudogap at the Fermi surface with a size set by doping
Summary
Nuclear magnetic resonance (NMR) provides important local information about the electronic properties of materials [1], and it has played a key role in the characterization of cuprate high-temperature superconductors [2,3]. The NMR spin shift that is proportional to the uniform electronic spin susceptibility is temperature-independent, as the increase in temperature decreases the occupation difference These elements of observation were the backdrop against which the cuprate NMR data were discussed, early on. No enhanced, special spin fluctuations are present in the underdoped systems This leaves, as an explanation for the failure of the Korringa relaxation (discovered early on [3]), only a suppression of the NMR shifts [22]. Matter 2020, 5, 66 states close to the lowest energies (at the Fermi surface) for the underdoped materials, and this gap is temperature-independent, but set by doping, different from what is often assumed [29,30] This scenario is in agreement with early specific heat data [31] that discussed such a pseudogap in YBa2Cu3O7−δ. Nuclear relaxation of planar oxygen shows strikingly simple behavior in these most studied materials, and we will find the conclusions to be generic to the cuprates
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
